author | tonyp |
Thu, 22 Jul 2010 10:27:41 -0400 | |
changeset 6248 | 2e661807cef0 |
parent 5920 | 8fdbb85e62d3 |
child 6975 | dc9b63952682 |
permissions | -rw-r--r-- |
1 | 1 |
/* |
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* Copyright (c) 1998, 2009, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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||
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# include "incls/_precompiled.incl" |
|
26 |
# include "incls/_synchronizer.cpp.incl" |
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||
28 |
#if defined(__GNUC__) && !defined(IA64) |
|
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// Need to inhibit inlining for older versions of GCC to avoid build-time failures |
|
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#define ATTR __attribute__((noinline)) |
|
31 |
#else |
|
32 |
#define ATTR |
|
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#endif |
|
34 |
||
35 |
// Native markword accessors for synchronization and hashCode(). |
|
36 |
// |
|
37 |
// The "core" versions of monitor enter and exit reside in this file. |
|
38 |
// The interpreter and compilers contain specialized transliterated |
|
39 |
// variants of the enter-exit fast-path operations. See i486.ad fast_lock(), |
|
40 |
// for instance. If you make changes here, make sure to modify the |
|
41 |
// interpreter, and both C1 and C2 fast-path inline locking code emission. |
|
42 |
// |
|
43 |
// TODO: merge the objectMonitor and synchronizer classes. |
|
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// |
|
45 |
// ----------------------------------------------------------------------------- |
|
46 |
||
47 |
#ifdef DTRACE_ENABLED |
|
48 |
||
49 |
// Only bother with this argument setup if dtrace is available |
|
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// TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. |
|
51 |
||
52 |
HS_DTRACE_PROBE_DECL5(hotspot, monitor__wait, |
|
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jlong, uintptr_t, char*, int, long); |
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HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited, |
|
55 |
jlong, uintptr_t, char*, int); |
|
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HS_DTRACE_PROBE_DECL4(hotspot, monitor__notify, |
|
57 |
jlong, uintptr_t, char*, int); |
|
58 |
HS_DTRACE_PROBE_DECL4(hotspot, monitor__notifyAll, |
|
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jlong, uintptr_t, char*, int); |
|
60 |
HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__enter, |
|
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jlong, uintptr_t, char*, int); |
|
62 |
HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__entered, |
|
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jlong, uintptr_t, char*, int); |
|
64 |
HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__exit, |
|
65 |
jlong, uintptr_t, char*, int); |
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66 |
||
67 |
#define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread) \ |
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char* bytes = NULL; \ |
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int len = 0; \ |
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jlong jtid = SharedRuntime::get_java_tid(thread); \ |
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symbolOop klassname = ((oop)(klassOop))->klass()->klass_part()->name(); \ |
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if (klassname != NULL) { \ |
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bytes = (char*)klassname->bytes(); \ |
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len = klassname->utf8_length(); \ |
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} |
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||
77 |
#define DTRACE_MONITOR_WAIT_PROBE(monitor, klassOop, thread, millis) \ |
|
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{ \ |
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if (DTraceMonitorProbes) { \ |
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DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ |
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HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid, \ |
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(monitor), bytes, len, (millis)); \ |
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} \ |
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} |
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86 |
#define DTRACE_MONITOR_PROBE(probe, monitor, klassOop, thread) \ |
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{ \ |
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if (DTraceMonitorProbes) { \ |
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DTRACE_MONITOR_PROBE_COMMON(klassOop, thread); \ |
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HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid, \ |
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(uintptr_t)(monitor), bytes, len); \ |
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} \ |
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} |
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94 |
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#else // ndef DTRACE_ENABLED |
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#define DTRACE_MONITOR_WAIT_PROBE(klassOop, thread, millis, mon) {;} |
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#define DTRACE_MONITOR_PROBE(probe, klassOop, thread, mon) {;} |
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||
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#endif // ndef DTRACE_ENABLED |
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||
102 |
// ObjectWaiter serves as a "proxy" or surrogate thread. |
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// TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific |
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// ParkEvent instead. Beware, however, that the JVMTI code |
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// knows about ObjectWaiters, so we'll have to reconcile that code. |
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// See next_waiter(), first_waiter(), etc. |
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||
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class ObjectWaiter : public StackObj { |
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public: |
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enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ } ; |
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enum Sorted { PREPEND, APPEND, SORTED } ; |
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ObjectWaiter * volatile _next; |
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ObjectWaiter * volatile _prev; |
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Thread* _thread; |
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ParkEvent * _event; |
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volatile int _notified ; |
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volatile TStates TState ; |
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Sorted _Sorted ; // List placement disposition |
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bool _active ; // Contention monitoring is enabled |
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public: |
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ObjectWaiter(Thread* thread) { |
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_next = NULL; |
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_prev = NULL; |
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_notified = 0; |
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TState = TS_RUN ; |
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_thread = thread; |
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_event = thread->_ParkEvent ; |
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_active = false; |
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assert (_event != NULL, "invariant") ; |
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} |
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void wait_reenter_begin(ObjectMonitor *mon) { |
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JavaThread *jt = (JavaThread *)this->_thread; |
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_active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(jt, mon); |
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} |
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||
137 |
void wait_reenter_end(ObjectMonitor *mon) { |
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JavaThread *jt = (JavaThread *)this->_thread; |
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JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(jt, _active); |
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} |
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}; |
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||
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enum ManifestConstants { |
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ClearResponsibleAtSTW = 0, |
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MaximumRecheckInterval = 1000 |
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} ; |
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||
148 |
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#undef TEVENT |
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#define TEVENT(nom) {if (SyncVerbose) FEVENT(nom); } |
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152 |
#define FEVENT(nom) { static volatile int ctr = 0 ; int v = ++ctr ; if ((v & (v-1)) == 0) { ::printf (#nom " : %d \n", v); ::fflush(stdout); }} |
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#undef TEVENT |
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#define TEVENT(nom) {;} |
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||
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// Performance concern: |
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// OrderAccess::storestore() calls release() which STs 0 into the global volatile |
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// OrderAccess::Dummy variable. This store is unnecessary for correctness. |
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// Many threads STing into a common location causes considerable cache migration |
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// or "sloshing" on large SMP system. As such, I avoid using OrderAccess::storestore() |
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// until it's repaired. In some cases OrderAccess::fence() -- which incurs local |
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// latency on the executing processor -- is a better choice as it scales on SMP |
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// systems. See http://blogs.sun.com/dave/entry/biased_locking_in_hotspot for a |
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// discussion of coherency costs. Note that all our current reference platforms |
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// provide strong ST-ST order, so the issue is moot on IA32, x64, and SPARC. |
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// |
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// As a general policy we use "volatile" to control compiler-based reordering |
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// and explicit fences (barriers) to control for architectural reordering performed |
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// by the CPU(s) or platform. |
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static int MBFence (int x) { OrderAccess::fence(); return x; } |
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||
174 |
struct SharedGlobals { |
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175 |
// These are highly shared mostly-read variables. |
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176 |
// To avoid false-sharing they need to be the sole occupants of a $ line. |
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double padPrefix [8]; |
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178 |
volatile int stwRandom ; |
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volatile int stwCycle ; |
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180 |
||
181 |
// Hot RW variables -- Sequester to avoid false-sharing |
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double padSuffix [16]; |
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volatile int hcSequence ; |
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double padFinal [8] ; |
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} ; |
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187 |
static SharedGlobals GVars ; |
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static int MonitorScavengeThreshold = 1000000 ; |
189 |
static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending |
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191 |
||
192 |
// Tunables ... |
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193 |
// The knob* variables are effectively final. Once set they should |
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// never be modified hence. Consider using __read_mostly with GCC. |
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195 |
||
196 |
static int Knob_LogSpins = 0 ; // enable jvmstat tally for spins |
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197 |
static int Knob_HandOff = 0 ; |
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198 |
static int Knob_Verbose = 0 ; |
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199 |
static int Knob_ReportSettings = 0 ; |
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200 |
||
201 |
static int Knob_SpinLimit = 5000 ; // derived by an external tool - |
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static int Knob_SpinBase = 0 ; // Floor AKA SpinMin |
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static int Knob_SpinBackOff = 0 ; // spin-loop backoff |
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static int Knob_CASPenalty = -1 ; // Penalty for failed CAS |
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static int Knob_OXPenalty = -1 ; // Penalty for observed _owner change |
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static int Knob_SpinSetSucc = 1 ; // spinners set the _succ field |
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static int Knob_SpinEarly = 1 ; |
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static int Knob_SuccEnabled = 1 ; // futile wake throttling |
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static int Knob_SuccRestrict = 0 ; // Limit successors + spinners to at-most-one |
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static int Knob_MaxSpinners = -1 ; // Should be a function of # CPUs |
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static int Knob_Bonus = 100 ; // spin success bonus |
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212 |
static int Knob_BonusB = 100 ; // spin success bonus |
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213 |
static int Knob_Penalty = 200 ; // spin failure penalty |
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214 |
static int Knob_Poverty = 1000 ; |
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215 |
static int Knob_SpinAfterFutile = 1 ; // Spin after returning from park() |
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216 |
static int Knob_FixedSpin = 0 ; |
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217 |
static int Knob_OState = 3 ; // Spinner checks thread state of _owner |
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218 |
static int Knob_UsePause = 1 ; |
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219 |
static int Knob_ExitPolicy = 0 ; |
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220 |
static int Knob_PreSpin = 10 ; // 20-100 likely better |
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221 |
static int Knob_ResetEvent = 0 ; |
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222 |
static int BackOffMask = 0 ; |
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223 |
||
224 |
static int Knob_FastHSSEC = 0 ; |
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225 |
static int Knob_MoveNotifyee = 2 ; // notify() - disposition of notifyee |
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static int Knob_QMode = 0 ; // EntryList-cxq policy - queue discipline |
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static volatile int InitDone = 0 ; |
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228 |
||
229 |
||
230 |
// hashCode() generation : |
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231 |
// |
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232 |
// Possibilities: |
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233 |
// * MD5Digest of {obj,stwRandom} |
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// * CRC32 of {obj,stwRandom} or any linear-feedback shift register function. |
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235 |
// * A DES- or AES-style SBox[] mechanism |
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236 |
// * One of the Phi-based schemes, such as: |
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237 |
// 2654435761 = 2^32 * Phi (golden ratio) |
|
238 |
// HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; |
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239 |
// * A variation of Marsaglia's shift-xor RNG scheme. |
|
240 |
// * (obj ^ stwRandom) is appealing, but can result |
|
241 |
// in undesirable regularity in the hashCode values of adjacent objects |
|
242 |
// (objects allocated back-to-back, in particular). This could potentially |
|
243 |
// result in hashtable collisions and reduced hashtable efficiency. |
|
244 |
// There are simple ways to "diffuse" the middle address bits over the |
|
245 |
// generated hashCode values: |
|
246 |
// |
|
247 |
||
248 |
static inline intptr_t get_next_hash(Thread * Self, oop obj) { |
|
249 |
intptr_t value = 0 ; |
|
250 |
if (hashCode == 0) { |
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251 |
// This form uses an unguarded global Park-Miller RNG, |
|
252 |
// so it's possible for two threads to race and generate the same RNG. |
|
253 |
// On MP system we'll have lots of RW access to a global, so the |
|
254 |
// mechanism induces lots of coherency traffic. |
|
255 |
value = os::random() ; |
|
256 |
} else |
|
257 |
if (hashCode == 1) { |
|
258 |
// This variation has the property of being stable (idempotent) |
|
259 |
// between STW operations. This can be useful in some of the 1-0 |
|
260 |
// synchronization schemes. |
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261 |
intptr_t addrBits = intptr_t(obj) >> 3 ; |
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262 |
value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ; |
|
263 |
} else |
|
264 |
if (hashCode == 2) { |
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265 |
value = 1 ; // for sensitivity testing |
|
266 |
} else |
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267 |
if (hashCode == 3) { |
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268 |
value = ++GVars.hcSequence ; |
|
269 |
} else |
|
270 |
if (hashCode == 4) { |
|
271 |
value = intptr_t(obj) ; |
|
272 |
} else { |
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273 |
// Marsaglia's xor-shift scheme with thread-specific state |
|
274 |
// This is probably the best overall implementation -- we'll |
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275 |
// likely make this the default in future releases. |
|
276 |
unsigned t = Self->_hashStateX ; |
|
277 |
t ^= (t << 11) ; |
|
278 |
Self->_hashStateX = Self->_hashStateY ; |
|
279 |
Self->_hashStateY = Self->_hashStateZ ; |
|
280 |
Self->_hashStateZ = Self->_hashStateW ; |
|
281 |
unsigned v = Self->_hashStateW ; |
|
282 |
v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ; |
|
283 |
Self->_hashStateW = v ; |
|
284 |
value = v ; |
|
285 |
} |
|
286 |
||
287 |
value &= markOopDesc::hash_mask; |
|
288 |
if (value == 0) value = 0xBAD ; |
|
289 |
assert (value != markOopDesc::no_hash, "invariant") ; |
|
290 |
TEVENT (hashCode: GENERATE) ; |
|
291 |
return value; |
|
292 |
} |
|
293 |
||
294 |
void BasicLock::print_on(outputStream* st) const { |
|
295 |
st->print("monitor"); |
|
296 |
} |
|
297 |
||
298 |
void BasicLock::move_to(oop obj, BasicLock* dest) { |
|
299 |
// Check to see if we need to inflate the lock. This is only needed |
|
300 |
// if an object is locked using "this" lightweight monitor. In that |
|
301 |
// case, the displaced_header() is unlocked, because the |
|
302 |
// displaced_header() contains the header for the originally unlocked |
|
303 |
// object. However the object could have already been inflated. But it |
|
304 |
// does not matter, the inflation will just a no-op. For other cases, |
|
305 |
// the displaced header will be either 0x0 or 0x3, which are location |
|
306 |
// independent, therefore the BasicLock is free to move. |
|
307 |
// |
|
308 |
// During OSR we may need to relocate a BasicLock (which contains a |
|
309 |
// displaced word) from a location in an interpreter frame to a |
|
310 |
// new location in a compiled frame. "this" refers to the source |
|
311 |
// basiclock in the interpreter frame. "dest" refers to the destination |
|
312 |
// basiclock in the new compiled frame. We *always* inflate in move_to(). |
|
313 |
// The always-Inflate policy works properly, but in 1.5.0 it can sometimes |
|
314 |
// cause performance problems in code that makes heavy use of a small # of |
|
315 |
// uncontended locks. (We'd inflate during OSR, and then sync performance |
|
316 |
// would subsequently plummet because the thread would be forced thru the slow-path). |
|
317 |
// This problem has been made largely moot on IA32 by inlining the inflated fast-path |
|
318 |
// operations in Fast_Lock and Fast_Unlock in i486.ad. |
|
319 |
// |
|
320 |
// Note that there is a way to safely swing the object's markword from |
|
321 |
// one stack location to another. This avoids inflation. Obviously, |
|
322 |
// we need to ensure that both locations refer to the current thread's stack. |
|
323 |
// There are some subtle concurrency issues, however, and since the benefit is |
|
324 |
// is small (given the support for inflated fast-path locking in the fast_lock, etc) |
|
325 |
// we'll leave that optimization for another time. |
|
326 |
||
327 |
if (displaced_header()->is_neutral()) { |
|
328 |
ObjectSynchronizer::inflate_helper(obj); |
|
329 |
// WARNING: We can not put check here, because the inflation |
|
330 |
// will not update the displaced header. Once BasicLock is inflated, |
|
331 |
// no one should ever look at its content. |
|
332 |
} else { |
|
333 |
// Typically the displaced header will be 0 (recursive stack lock) or |
|
334 |
// unused_mark. Naively we'd like to assert that the displaced mark |
|
335 |
// value is either 0, neutral, or 3. But with the advent of the |
|
336 |
// store-before-CAS avoidance in fast_lock/compiler_lock_object |
|
337 |
// we can find any flavor mark in the displaced mark. |
|
338 |
} |
|
339 |
// [RGV] The next line appears to do nothing! |
|
340 |
intptr_t dh = (intptr_t) displaced_header(); |
|
341 |
dest->set_displaced_header(displaced_header()); |
|
342 |
} |
|
343 |
||
344 |
// ----------------------------------------------------------------------------- |
|
345 |
||
346 |
// standard constructor, allows locking failures |
|
347 |
ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) { |
|
348 |
_dolock = doLock; |
|
349 |
_thread = thread; |
|
350 |
debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);) |
|
351 |
_obj = obj; |
|
352 |
||
353 |
if (_dolock) { |
|
354 |
TEVENT (ObjectLocker) ; |
|
355 |
||
356 |
ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread); |
|
357 |
} |
|
358 |
} |
|
359 |
||
360 |
ObjectLocker::~ObjectLocker() { |
|
361 |
if (_dolock) { |
|
362 |
ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread); |
|
363 |
} |
|
364 |
} |
|
365 |
||
366 |
// ----------------------------------------------------------------------------- |
|
367 |
||
368 |
||
369 |
PerfCounter * ObjectSynchronizer::_sync_Inflations = NULL ; |
|
370 |
PerfCounter * ObjectSynchronizer::_sync_Deflations = NULL ; |
|
371 |
PerfCounter * ObjectSynchronizer::_sync_ContendedLockAttempts = NULL ; |
|
372 |
PerfCounter * ObjectSynchronizer::_sync_FutileWakeups = NULL ; |
|
373 |
PerfCounter * ObjectSynchronizer::_sync_Parks = NULL ; |
|
374 |
PerfCounter * ObjectSynchronizer::_sync_EmptyNotifications = NULL ; |
|
375 |
PerfCounter * ObjectSynchronizer::_sync_Notifications = NULL ; |
|
376 |
PerfCounter * ObjectSynchronizer::_sync_PrivateA = NULL ; |
|
377 |
PerfCounter * ObjectSynchronizer::_sync_PrivateB = NULL ; |
|
378 |
PerfCounter * ObjectSynchronizer::_sync_SlowExit = NULL ; |
|
379 |
PerfCounter * ObjectSynchronizer::_sync_SlowEnter = NULL ; |
|
380 |
PerfCounter * ObjectSynchronizer::_sync_SlowNotify = NULL ; |
|
381 |
PerfCounter * ObjectSynchronizer::_sync_SlowNotifyAll = NULL ; |
|
382 |
PerfCounter * ObjectSynchronizer::_sync_FailedSpins = NULL ; |
|
383 |
PerfCounter * ObjectSynchronizer::_sync_SuccessfulSpins = NULL ; |
|
384 |
PerfCounter * ObjectSynchronizer::_sync_MonInCirculation = NULL ; |
|
385 |
PerfCounter * ObjectSynchronizer::_sync_MonScavenged = NULL ; |
|
386 |
PerfLongVariable * ObjectSynchronizer::_sync_MonExtant = NULL ; |
|
387 |
||
388 |
// One-shot global initialization for the sync subsystem. |
|
389 |
// We could also defer initialization and initialize on-demand |
|
390 |
// the first time we call inflate(). Initialization would |
|
391 |
// be protected - like so many things - by the MonitorCache_lock. |
|
392 |
||
393 |
void ObjectSynchronizer::Initialize () { |
|
394 |
static int InitializationCompleted = 0 ; |
|
395 |
assert (InitializationCompleted == 0, "invariant") ; |
|
396 |
InitializationCompleted = 1 ; |
|
397 |
if (UsePerfData) { |
|
398 |
EXCEPTION_MARK ; |
|
399 |
#define NEWPERFCOUNTER(n) {n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,CHECK); } |
|
400 |
#define NEWPERFVARIABLE(n) {n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,CHECK); } |
|
401 |
NEWPERFCOUNTER(_sync_Inflations) ; |
|
402 |
NEWPERFCOUNTER(_sync_Deflations) ; |
|
403 |
NEWPERFCOUNTER(_sync_ContendedLockAttempts) ; |
|
404 |
NEWPERFCOUNTER(_sync_FutileWakeups) ; |
|
405 |
NEWPERFCOUNTER(_sync_Parks) ; |
|
406 |
NEWPERFCOUNTER(_sync_EmptyNotifications) ; |
|
407 |
NEWPERFCOUNTER(_sync_Notifications) ; |
|
408 |
NEWPERFCOUNTER(_sync_SlowEnter) ; |
|
409 |
NEWPERFCOUNTER(_sync_SlowExit) ; |
|
410 |
NEWPERFCOUNTER(_sync_SlowNotify) ; |
|
411 |
NEWPERFCOUNTER(_sync_SlowNotifyAll) ; |
|
412 |
NEWPERFCOUNTER(_sync_FailedSpins) ; |
|
413 |
NEWPERFCOUNTER(_sync_SuccessfulSpins) ; |
|
414 |
NEWPERFCOUNTER(_sync_PrivateA) ; |
|
415 |
NEWPERFCOUNTER(_sync_PrivateB) ; |
|
416 |
NEWPERFCOUNTER(_sync_MonInCirculation) ; |
|
417 |
NEWPERFCOUNTER(_sync_MonScavenged) ; |
|
418 |
NEWPERFVARIABLE(_sync_MonExtant) ; |
|
419 |
#undef NEWPERFCOUNTER |
|
420 |
} |
|
421 |
} |
|
422 |
||
423 |
// Compile-time asserts |
|
424 |
// When possible, it's better to catch errors deterministically at |
|
425 |
// compile-time than at runtime. The down-side to using compile-time |
|
426 |
// asserts is that error message -- often something about negative array |
|
427 |
// indices -- is opaque. |
|
428 |
||
1889
24b003a6fe46
6781583: Hotspot build fails on linux 64 bit platform with gcc 4.3.2
xlu
parents:
1665
diff
changeset
|
429 |
#define CTASSERT(x) { int tag[1-(2*!(x))]; printf ("Tag @" INTPTR_FORMAT "\n", (intptr_t)tag); } |
1 | 430 |
|
431 |
void ObjectMonitor::ctAsserts() { |
|
432 |
CTASSERT(offset_of (ObjectMonitor, _header) == 0); |
|
433 |
} |
|
434 |
||
435 |
static int Adjust (volatile int * adr, int dx) { |
|
436 |
int v ; |
|
437 |
for (v = *adr ; Atomic::cmpxchg (v + dx, adr, v) != v; v = *adr) ; |
|
438 |
return v ; |
|
439 |
} |
|
440 |
||
441 |
// Ad-hoc mutual exclusion primitives: SpinLock and Mux |
|
442 |
// |
|
443 |
// We employ SpinLocks _only for low-contention, fixed-length |
|
444 |
// short-duration critical sections where we're concerned |
|
445 |
// about native mutex_t or HotSpot Mutex:: latency. |
|
446 |
// The mux construct provides a spin-then-block mutual exclusion |
|
447 |
// mechanism. |
|
448 |
// |
|
449 |
// Testing has shown that contention on the ListLock guarding gFreeList |
|
450 |
// is common. If we implement ListLock as a simple SpinLock it's common |
|
451 |
// for the JVM to devolve to yielding with little progress. This is true |
|
452 |
// despite the fact that the critical sections protected by ListLock are |
|
453 |
// extremely short. |
|
454 |
// |
|
455 |
// TODO-FIXME: ListLock should be of type SpinLock. |
|
456 |
// We should make this a 1st-class type, integrated into the lock |
|
457 |
// hierarchy as leaf-locks. Critically, the SpinLock structure |
|
458 |
// should have sufficient padding to avoid false-sharing and excessive |
|
459 |
// cache-coherency traffic. |
|
460 |
||
461 |
||
462 |
typedef volatile int SpinLockT ; |
|
463 |
||
464 |
void Thread::SpinAcquire (volatile int * adr, const char * LockName) { |
|
465 |
if (Atomic::cmpxchg (1, adr, 0) == 0) { |
|
466 |
return ; // normal fast-path return |
|
467 |
} |
|
468 |
||
469 |
// Slow-path : We've encountered contention -- Spin/Yield/Block strategy. |
|
470 |
TEVENT (SpinAcquire - ctx) ; |
|
471 |
int ctr = 0 ; |
|
472 |
int Yields = 0 ; |
|
473 |
for (;;) { |
|
474 |
while (*adr != 0) { |
|
475 |
++ctr ; |
|
476 |
if ((ctr & 0xFFF) == 0 || !os::is_MP()) { |
|
477 |
if (Yields > 5) { |
|
478 |
// Consider using a simple NakedSleep() instead. |
|
479 |
// Then SpinAcquire could be called by non-JVM threads |
|
480 |
Thread::current()->_ParkEvent->park(1) ; |
|
481 |
} else { |
|
482 |
os::NakedYield() ; |
|
483 |
++Yields ; |
|
484 |
} |
|
485 |
} else { |
|
486 |
SpinPause() ; |
|
487 |
} |
|
488 |
} |
|
489 |
if (Atomic::cmpxchg (1, adr, 0) == 0) return ; |
|
490 |
} |
|
491 |
} |
|
492 |
||
493 |
void Thread::SpinRelease (volatile int * adr) { |
|
494 |
assert (*adr != 0, "invariant") ; |
|
495 |
OrderAccess::fence() ; // guarantee at least release consistency. |
|
496 |
// Roach-motel semantics. |
|
497 |
// It's safe if subsequent LDs and STs float "up" into the critical section, |
|
498 |
// but prior LDs and STs within the critical section can't be allowed |
|
499 |
// to reorder or float past the ST that releases the lock. |
|
500 |
*adr = 0 ; |
|
501 |
} |
|
502 |
||
503 |
// muxAcquire and muxRelease: |
|
504 |
// |
|
505 |
// * muxAcquire and muxRelease support a single-word lock-word construct. |
|
506 |
// The LSB of the word is set IFF the lock is held. |
|
507 |
// The remainder of the word points to the head of a singly-linked list |
|
508 |
// of threads blocked on the lock. |
|
509 |
// |
|
510 |
// * The current implementation of muxAcquire-muxRelease uses its own |
|
511 |
// dedicated Thread._MuxEvent instance. If we're interested in |
|
512 |
// minimizing the peak number of extant ParkEvent instances then |
|
513 |
// we could eliminate _MuxEvent and "borrow" _ParkEvent as long |
|
514 |
// as certain invariants were satisfied. Specifically, care would need |
|
515 |
// to be taken with regards to consuming unpark() "permits". |
|
516 |
// A safe rule of thumb is that a thread would never call muxAcquire() |
|
517 |
// if it's enqueued (cxq, EntryList, WaitList, etc) and will subsequently |
|
518 |
// park(). Otherwise the _ParkEvent park() operation in muxAcquire() could |
|
519 |
// consume an unpark() permit intended for monitorenter, for instance. |
|
520 |
// One way around this would be to widen the restricted-range semaphore |
|
521 |
// implemented in park(). Another alternative would be to provide |
|
522 |
// multiple instances of the PlatformEvent() for each thread. One |
|
523 |
// instance would be dedicated to muxAcquire-muxRelease, for instance. |
|
524 |
// |
|
525 |
// * Usage: |
|
526 |
// -- Only as leaf locks |
|
527 |
// -- for short-term locking only as muxAcquire does not perform |
|
528 |
// thread state transitions. |
|
529 |
// |
|
530 |
// Alternatives: |
|
531 |
// * We could implement muxAcquire and muxRelease with MCS or CLH locks |
|
532 |
// but with parking or spin-then-park instead of pure spinning. |
|
533 |
// * Use Taura-Oyama-Yonenzawa locks. |
|
534 |
// * It's possible to construct a 1-0 lock if we encode the lockword as |
|
535 |
// (List,LockByte). Acquire will CAS the full lockword while Release |
|
536 |
// will STB 0 into the LockByte. The 1-0 scheme admits stranding, so |
|
537 |
// acquiring threads use timers (ParkTimed) to detect and recover from |
|
538 |
// the stranding window. Thread/Node structures must be aligned on 256-byte |
|
539 |
// boundaries by using placement-new. |
|
540 |
// * Augment MCS with advisory back-link fields maintained with CAS(). |
|
541 |
// Pictorially: LockWord -> T1 <-> T2 <-> T3 <-> ... <-> Tn <-> Owner. |
|
542 |
// The validity of the backlinks must be ratified before we trust the value. |
|
543 |
// If the backlinks are invalid the exiting thread must back-track through the |
|
544 |
// the forward links, which are always trustworthy. |
|
545 |
// * Add a successor indication. The LockWord is currently encoded as |
|
546 |
// (List, LOCKBIT:1). We could also add a SUCCBIT or an explicit _succ variable |
|
547 |
// to provide the usual futile-wakeup optimization. |
|
548 |
// See RTStt for details. |
|
549 |
// * Consider schedctl.sc_nopreempt to cover the critical section. |
|
550 |
// |
|
551 |
||
552 |
||
553 |
typedef volatile intptr_t MutexT ; // Mux Lock-word |
|
554 |
enum MuxBits { LOCKBIT = 1 } ; |
|
555 |
||
556 |
void Thread::muxAcquire (volatile intptr_t * Lock, const char * LockName) { |
|
557 |
intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ; |
|
558 |
if (w == 0) return ; |
|
559 |
if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
560 |
return ; |
|
561 |
} |
|
562 |
||
563 |
TEVENT (muxAcquire - Contention) ; |
|
564 |
ParkEvent * const Self = Thread::current()->_MuxEvent ; |
|
565 |
assert ((intptr_t(Self) & LOCKBIT) == 0, "invariant") ; |
|
566 |
for (;;) { |
|
567 |
int its = (os::is_MP() ? 100 : 0) + 1 ; |
|
568 |
||
569 |
// Optional spin phase: spin-then-park strategy |
|
570 |
while (--its >= 0) { |
|
571 |
w = *Lock ; |
|
572 |
if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
573 |
return ; |
|
574 |
} |
|
575 |
} |
|
576 |
||
577 |
Self->reset() ; |
|
578 |
Self->OnList = intptr_t(Lock) ; |
|
579 |
// The following fence() isn't _strictly necessary as the subsequent |
|
580 |
// CAS() both serializes execution and ratifies the fetched *Lock value. |
|
581 |
OrderAccess::fence(); |
|
582 |
for (;;) { |
|
583 |
w = *Lock ; |
|
584 |
if ((w & LOCKBIT) == 0) { |
|
585 |
if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
586 |
Self->OnList = 0 ; // hygiene - allows stronger asserts |
|
587 |
return ; |
|
588 |
} |
|
589 |
continue ; // Interference -- *Lock changed -- Just retry |
|
590 |
} |
|
591 |
assert (w & LOCKBIT, "invariant") ; |
|
592 |
Self->ListNext = (ParkEvent *) (w & ~LOCKBIT ); |
|
593 |
if (Atomic::cmpxchg_ptr (intptr_t(Self)|LOCKBIT, Lock, w) == w) break ; |
|
594 |
} |
|
595 |
||
596 |
while (Self->OnList != 0) { |
|
597 |
Self->park() ; |
|
598 |
} |
|
599 |
} |
|
600 |
} |
|
601 |
||
602 |
void Thread::muxAcquireW (volatile intptr_t * Lock, ParkEvent * ev) { |
|
603 |
intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ; |
|
604 |
if (w == 0) return ; |
|
605 |
if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
606 |
return ; |
|
607 |
} |
|
608 |
||
609 |
TEVENT (muxAcquire - Contention) ; |
|
610 |
ParkEvent * ReleaseAfter = NULL ; |
|
611 |
if (ev == NULL) { |
|
612 |
ev = ReleaseAfter = ParkEvent::Allocate (NULL) ; |
|
613 |
} |
|
614 |
assert ((intptr_t(ev) & LOCKBIT) == 0, "invariant") ; |
|
615 |
for (;;) { |
|
616 |
guarantee (ev->OnList == 0, "invariant") ; |
|
617 |
int its = (os::is_MP() ? 100 : 0) + 1 ; |
|
618 |
||
619 |
// Optional spin phase: spin-then-park strategy |
|
620 |
while (--its >= 0) { |
|
621 |
w = *Lock ; |
|
622 |
if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
623 |
if (ReleaseAfter != NULL) { |
|
624 |
ParkEvent::Release (ReleaseAfter) ; |
|
625 |
} |
|
626 |
return ; |
|
627 |
} |
|
628 |
} |
|
629 |
||
630 |
ev->reset() ; |
|
631 |
ev->OnList = intptr_t(Lock) ; |
|
632 |
// The following fence() isn't _strictly necessary as the subsequent |
|
633 |
// CAS() both serializes execution and ratifies the fetched *Lock value. |
|
634 |
OrderAccess::fence(); |
|
635 |
for (;;) { |
|
636 |
w = *Lock ; |
|
637 |
if ((w & LOCKBIT) == 0) { |
|
638 |
if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) { |
|
639 |
ev->OnList = 0 ; |
|
640 |
// We call ::Release while holding the outer lock, thus |
|
641 |
// artificially lengthening the critical section. |
|
642 |
// Consider deferring the ::Release() until the subsequent unlock(), |
|
643 |
// after we've dropped the outer lock. |
|
644 |
if (ReleaseAfter != NULL) { |
|
645 |
ParkEvent::Release (ReleaseAfter) ; |
|
646 |
} |
|
647 |
return ; |
|
648 |
} |
|
649 |
continue ; // Interference -- *Lock changed -- Just retry |
|
650 |
} |
|
651 |
assert (w & LOCKBIT, "invariant") ; |
|
652 |
ev->ListNext = (ParkEvent *) (w & ~LOCKBIT ); |
|
653 |
if (Atomic::cmpxchg_ptr (intptr_t(ev)|LOCKBIT, Lock, w) == w) break ; |
|
654 |
} |
|
655 |
||
656 |
while (ev->OnList != 0) { |
|
657 |
ev->park() ; |
|
658 |
} |
|
659 |
} |
|
660 |
} |
|
661 |
||
662 |
// Release() must extract a successor from the list and then wake that thread. |
|
663 |
// It can "pop" the front of the list or use a detach-modify-reattach (DMR) scheme |
|
664 |
// similar to that used by ParkEvent::Allocate() and ::Release(). DMR-based |
|
665 |
// Release() would : |
|
666 |
// (A) CAS() or swap() null to *Lock, releasing the lock and detaching the list. |
|
667 |
// (B) Extract a successor from the private list "in-hand" |
|
668 |
// (C) attempt to CAS() the residual back into *Lock over null. |
|
669 |
// If there were any newly arrived threads and the CAS() would fail. |
|
670 |
// In that case Release() would detach the RATs, re-merge the list in-hand |
|
671 |
// with the RATs and repeat as needed. Alternately, Release() might |
|
672 |
// detach and extract a successor, but then pass the residual list to the wakee. |
|
673 |
// The wakee would be responsible for reattaching and remerging before it |
|
674 |
// competed for the lock. |
|
675 |
// |
|
676 |
// Both "pop" and DMR are immune from ABA corruption -- there can be |
|
677 |
// multiple concurrent pushers, but only one popper or detacher. |
|
678 |
// This implementation pops from the head of the list. This is unfair, |
|
679 |
// but tends to provide excellent throughput as hot threads remain hot. |
|
680 |
// (We wake recently run threads first). |
|
681 |
||
682 |
void Thread::muxRelease (volatile intptr_t * Lock) { |
|
683 |
for (;;) { |
|
684 |
const intptr_t w = Atomic::cmpxchg_ptr (0, Lock, LOCKBIT) ; |
|
685 |
assert (w & LOCKBIT, "invariant") ; |
|
686 |
if (w == LOCKBIT) return ; |
|
687 |
ParkEvent * List = (ParkEvent *) (w & ~LOCKBIT) ; |
|
688 |
assert (List != NULL, "invariant") ; |
|
689 |
assert (List->OnList == intptr_t(Lock), "invariant") ; |
|
690 |
ParkEvent * nxt = List->ListNext ; |
|
691 |
||
692 |
// The following CAS() releases the lock and pops the head element. |
|
693 |
if (Atomic::cmpxchg_ptr (intptr_t(nxt), Lock, w) != w) { |
|
694 |
continue ; |
|
695 |
} |
|
696 |
List->OnList = 0 ; |
|
697 |
OrderAccess::fence() ; |
|
698 |
List->unpark () ; |
|
699 |
return ; |
|
700 |
} |
|
701 |
} |
|
702 |
||
703 |
// ObjectMonitor Lifecycle |
|
704 |
// ----------------------- |
|
705 |
// Inflation unlinks monitors from the global gFreeList and |
|
706 |
// associates them with objects. Deflation -- which occurs at |
|
707 |
// STW-time -- disassociates idle monitors from objects. Such |
|
708 |
// scavenged monitors are returned to the gFreeList. |
|
709 |
// |
|
710 |
// The global list is protected by ListLock. All the critical sections |
|
711 |
// are short and operate in constant-time. |
|
712 |
// |
|
713 |
// ObjectMonitors reside in type-stable memory (TSM) and are immortal. |
|
714 |
// |
|
715 |
// Lifecycle: |
|
716 |
// -- unassigned and on the global free list |
|
717 |
// -- unassigned and on a thread's private omFreeList |
|
718 |
// -- assigned to an object. The object is inflated and the mark refers |
|
719 |
// to the objectmonitor. |
|
720 |
// |
|
721 |
// TODO-FIXME: |
|
722 |
// |
|
723 |
// * We currently protect the gFreeList with a simple lock. |
|
724 |
// An alternate lock-free scheme would be to pop elements from the gFreeList |
|
725 |
// with CAS. This would be safe from ABA corruption as long we only |
|
726 |
// recycled previously appearing elements onto the list in deflate_idle_monitors() |
|
727 |
// at STW-time. Completely new elements could always be pushed onto the gFreeList |
|
728 |
// with CAS. Elements that appeared previously on the list could only |
|
729 |
// be installed at STW-time. |
|
730 |
// |
|
731 |
// * For efficiency and to help reduce the store-before-CAS penalty |
|
732 |
// the objectmonitors on gFreeList or local free lists should be ready to install |
|
733 |
// with the exception of _header and _object. _object can be set after inflation. |
|
734 |
// In particular, keep all objectMonitors on a thread's private list in ready-to-install |
|
735 |
// state with m.Owner set properly. |
|
736 |
// |
|
737 |
// * We could all diffuse contention by using multiple global (FreeList, Lock) |
|
738 |
// pairs -- threads could use trylock() and a cyclic-scan strategy to search for |
|
739 |
// an unlocked free list. |
|
740 |
// |
|
741 |
// * Add lifecycle tags and assert()s. |
|
742 |
// |
|
743 |
// * Be more consistent about when we clear an objectmonitor's fields: |
|
744 |
// A. After extracting the objectmonitor from a free list. |
|
745 |
// B. After adding an objectmonitor to a free list. |
|
746 |
// |
|
747 |
||
748 |
ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ; |
|
749 |
ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ; |
|
5920
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
750 |
ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
751 |
int ObjectSynchronizer::gOmInUseCount = 0; |
1 | 752 |
static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache |
5710 | 753 |
static volatile int MonitorFreeCount = 0 ; // # on gFreeList |
754 |
static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation |
|
1 | 755 |
#define CHAINMARKER ((oop)-1) |
756 |
||
5710 | 757 |
// Constraining monitor pool growth via MonitorBound ... |
758 |
// |
|
759 |
// The monitor pool is grow-only. We scavenge at STW safepoint-time, but the |
|
760 |
// the rate of scavenging is driven primarily by GC. As such, we can find |
|
761 |
// an inordinate number of monitors in circulation. |
|
762 |
// To avoid that scenario we can artificially induce a STW safepoint |
|
763 |
// if the pool appears to be growing past some reasonable bound. |
|
764 |
// Generally we favor time in space-time tradeoffs, but as there's no |
|
765 |
// natural back-pressure on the # of extant monitors we need to impose some |
|
766 |
// type of limit. Beware that if MonitorBound is set to too low a value |
|
767 |
// we could just loop. In addition, if MonitorBound is set to a low value |
|
768 |
// we'll incur more safepoints, which are harmful to performance. |
|
769 |
// See also: GuaranteedSafepointInterval |
|
770 |
// |
|
771 |
// As noted elsewhere, the correct long-term solution is to deflate at |
|
772 |
// monitorexit-time, in which case the number of inflated objects is bounded |
|
773 |
// by the number of threads. That policy obviates the need for scavenging at |
|
774 |
// STW safepoint time. As an aside, scavenging can be time-consuming when the |
|
775 |
// # of extant monitors is large. Unfortunately there's a day-1 assumption baked |
|
776 |
// into much HotSpot code that the object::monitor relationship, once established |
|
777 |
// or observed, will remain stable except over potential safepoints. |
|
778 |
// |
|
779 |
// We can use either a blocking synchronous VM operation or an async VM operation. |
|
780 |
// -- If we use a blocking VM operation : |
|
781 |
// Calls to ScavengeCheck() should be inserted only into 'safe' locations in paths |
|
782 |
// that lead to ::inflate() or ::omAlloc(). |
|
783 |
// Even though the safepoint will not directly induce GC, a GC might |
|
784 |
// piggyback on the safepoint operation, so the caller should hold no naked oops. |
|
785 |
// Furthermore, monitor::object relationships are NOT necessarily stable over this call |
|
786 |
// unless the caller has made provisions to "pin" the object to the monitor, say |
|
787 |
// by incrementing the monitor's _count field. |
|
788 |
// -- If we use a non-blocking asynchronous VM operation : |
|
789 |
// the constraints above don't apply. The safepoint will fire in the future |
|
790 |
// at a more convenient time. On the other hand the latency between posting and |
|
791 |
// running the safepoint introduces or admits "slop" or laxity during which the |
|
792 |
// monitor population can climb further above the threshold. The monitor population, |
|
793 |
// however, tends to converge asymptotically over time to a count that's slightly |
|
794 |
// above the target value specified by MonitorBound. That is, we avoid unbounded |
|
795 |
// growth, albeit with some imprecision. |
|
796 |
// |
|
797 |
// The current implementation uses asynchronous VM operations. |
|
798 |
// |
|
799 |
// Ideally we'd check if (MonitorPopulation > MonitorBound) in omAlloc() |
|
800 |
// immediately before trying to grow the global list via allocation. |
|
801 |
// If the predicate was true then we'd induce a synchronous safepoint, wait |
|
802 |
// for the safepoint to complete, and then again to allocate from the global |
|
803 |
// free list. This approach is much simpler and precise, admitting no "slop". |
|
804 |
// Unfortunately we can't safely safepoint in the midst of omAlloc(), so |
|
805 |
// instead we use asynchronous safepoints. |
|
806 |
||
807 |
static void InduceScavenge (Thread * Self, const char * Whence) { |
|
808 |
// Induce STW safepoint to trim monitors |
|
809 |
// Ultimately, this results in a call to deflate_idle_monitors() in the near future. |
|
810 |
// More precisely, trigger an asynchronous STW safepoint as the number |
|
811 |
// of active monitors passes the specified threshold. |
|
812 |
// TODO: assert thread state is reasonable |
|
813 |
||
814 |
if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) { |
|
815 |
if (Knob_Verbose) { |
|
816 |
::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
|
817 |
::fflush(stdout) ; |
|
818 |
} |
|
819 |
// Induce a 'null' safepoint to scavenge monitors |
|
820 |
// Must VM_Operation instance be heap allocated as the op will be enqueue and posted |
|
821 |
// to the VMthread and have a lifespan longer than that of this activation record. |
|
822 |
// The VMThread will delete the op when completed. |
|
823 |
VMThread::execute (new VM_ForceAsyncSafepoint()) ; |
|
824 |
||
825 |
if (Knob_Verbose) { |
|
826 |
::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ; |
|
827 |
::fflush(stdout) ; |
|
828 |
} |
|
829 |
} |
|
830 |
} |
|
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|
831 |
/* Too slow for general assert or debug |
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|
832 |
void ObjectSynchronizer::verifyInUse (Thread *Self) { |
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|
833 |
ObjectMonitor* mid; |
8fdbb85e62d3
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|
834 |
int inusetally = 0; |
8fdbb85e62d3
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|
835 |
for (mid = Self->omInUseList; mid != NULL; mid = mid->FreeNext) { |
8fdbb85e62d3
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|
836 |
inusetally ++; |
8fdbb85e62d3
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|
837 |
} |
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|
838 |
assert(inusetally == Self->omInUseCount, "inuse count off"); |
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|
839 |
|
8fdbb85e62d3
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|
840 |
int freetally = 0; |
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|
841 |
for (mid = Self->omFreeList; mid != NULL; mid = mid->FreeNext) { |
8fdbb85e62d3
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|
842 |
freetally ++; |
8fdbb85e62d3
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|
843 |
} |
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|
844 |
assert(freetally == Self->omFreeCount, "free count off"); |
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|
845 |
} |
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|
846 |
*/ |
5710 | 847 |
|
1 | 848 |
ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) { |
849 |
// A large MAXPRIVATE value reduces both list lock contention |
|
850 |
// and list coherency traffic, but also tends to increase the |
|
851 |
// number of objectMonitors in circulation as well as the STW |
|
852 |
// scavenge costs. As usual, we lean toward time in space-time |
|
853 |
// tradeoffs. |
|
854 |
const int MAXPRIVATE = 1024 ; |
|
855 |
for (;;) { |
|
856 |
ObjectMonitor * m ; |
|
857 |
||
858 |
// 1: try to allocate from the thread's local omFreeList. |
|
859 |
// Threads will attempt to allocate first from their local list, then |
|
860 |
// from the global list, and only after those attempts fail will the thread |
|
861 |
// attempt to instantiate new monitors. Thread-local free lists take |
|
862 |
// heat off the ListLock and improve allocation latency, as well as reducing |
|
863 |
// coherency traffic on the shared global list. |
|
864 |
m = Self->omFreeList ; |
|
865 |
if (m != NULL) { |
|
866 |
Self->omFreeList = m->FreeNext ; |
|
867 |
Self->omFreeCount -- ; |
|
868 |
// CONSIDER: set m->FreeNext = BAD -- diagnostic hygiene |
|
869 |
guarantee (m->object() == NULL, "invariant") ; |
|
5710 | 870 |
if (MonitorInUseLists) { |
871 |
m->FreeNext = Self->omInUseList; |
|
872 |
Self->omInUseList = m; |
|
873 |
Self->omInUseCount ++; |
|
5920
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|
874 |
// verifyInUse(Self); |
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|
875 |
} else { |
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|
876 |
m->FreeNext = NULL; |
5710 | 877 |
} |
1 | 878 |
return m ; |
879 |
} |
|
880 |
||
881 |
// 2: try to allocate from the global gFreeList |
|
882 |
// CONSIDER: use muxTry() instead of muxAcquire(). |
|
883 |
// If the muxTry() fails then drop immediately into case 3. |
|
884 |
// If we're using thread-local free lists then try |
|
885 |
// to reprovision the caller's free list. |
|
886 |
if (gFreeList != NULL) { |
|
887 |
// Reprovision the thread's omFreeList. |
|
888 |
// Use bulk transfers to reduce the allocation rate and heat |
|
889 |
// on various locks. |
|
890 |
Thread::muxAcquire (&ListLock, "omAlloc") ; |
|
891 |
for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL; ) { |
|
5710 | 892 |
MonitorFreeCount --; |
1 | 893 |
ObjectMonitor * take = gFreeList ; |
894 |
gFreeList = take->FreeNext ; |
|
895 |
guarantee (take->object() == NULL, "invariant") ; |
|
896 |
guarantee (!take->is_busy(), "invariant") ; |
|
897 |
take->Recycle() ; |
|
5920
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|
898 |
omRelease (Self, take, false) ; |
1 | 899 |
} |
900 |
Thread::muxRelease (&ListLock) ; |
|
901 |
Self->omFreeProvision += 1 + (Self->omFreeProvision/2) ; |
|
902 |
if (Self->omFreeProvision > MAXPRIVATE ) Self->omFreeProvision = MAXPRIVATE ; |
|
903 |
TEVENT (omFirst - reprovision) ; |
|
5710 | 904 |
|
905 |
const int mx = MonitorBound ; |
|
906 |
if (mx > 0 && (MonitorPopulation-MonitorFreeCount) > mx) { |
|
907 |
// We can't safely induce a STW safepoint from omAlloc() as our thread |
|
908 |
// state may not be appropriate for such activities and callers may hold |
|
909 |
// naked oops, so instead we defer the action. |
|
910 |
InduceScavenge (Self, "omAlloc") ; |
|
911 |
} |
|
912 |
continue; |
|
1 | 913 |
} |
914 |
||
915 |
// 3: allocate a block of new ObjectMonitors |
|
916 |
// Both the local and global free lists are empty -- resort to malloc(). |
|
917 |
// In the current implementation objectMonitors are TSM - immortal. |
|
918 |
assert (_BLOCKSIZE > 1, "invariant") ; |
|
919 |
ObjectMonitor * temp = new ObjectMonitor[_BLOCKSIZE]; |
|
920 |
||
921 |
// NOTE: (almost) no way to recover if allocation failed. |
|
922 |
// We might be able to induce a STW safepoint and scavenge enough |
|
923 |
// objectMonitors to permit progress. |
|
924 |
if (temp == NULL) { |
|
925 |
vm_exit_out_of_memory (sizeof (ObjectMonitor[_BLOCKSIZE]), "Allocate ObjectMonitors") ; |
|
926 |
} |
|
927 |
||
928 |
// Format the block. |
|
929 |
// initialize the linked list, each monitor points to its next |
|
930 |
// forming the single linked free list, the very first monitor |
|
931 |
// will points to next block, which forms the block list. |
|
932 |
// The trick of using the 1st element in the block as gBlockList |
|
933 |
// linkage should be reconsidered. A better implementation would |
|
934 |
// look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; } |
|
935 |
||
936 |
for (int i = 1; i < _BLOCKSIZE ; i++) { |
|
937 |
temp[i].FreeNext = &temp[i+1]; |
|
938 |
} |
|
939 |
||
940 |
// terminate the last monitor as the end of list |
|
941 |
temp[_BLOCKSIZE - 1].FreeNext = NULL ; |
|
942 |
||
943 |
// Element [0] is reserved for global list linkage |
|
944 |
temp[0].set_object(CHAINMARKER); |
|
945 |
||
946 |
// Consider carving out this thread's current request from the |
|
947 |
// block in hand. This avoids some lock traffic and redundant |
|
948 |
// list activity. |
|
949 |
||
950 |
// Acquire the ListLock to manipulate BlockList and FreeList. |
|
951 |
// An Oyama-Taura-Yonezawa scheme might be more efficient. |
|
952 |
Thread::muxAcquire (&ListLock, "omAlloc [2]") ; |
|
5710 | 953 |
MonitorPopulation += _BLOCKSIZE-1; |
954 |
MonitorFreeCount += _BLOCKSIZE-1; |
|
1 | 955 |
|
956 |
// Add the new block to the list of extant blocks (gBlockList). |
|
957 |
// The very first objectMonitor in a block is reserved and dedicated. |
|
958 |
// It serves as blocklist "next" linkage. |
|
959 |
temp[0].FreeNext = gBlockList; |
|
960 |
gBlockList = temp; |
|
961 |
||
962 |
// Add the new string of objectMonitors to the global free list |
|
963 |
temp[_BLOCKSIZE - 1].FreeNext = gFreeList ; |
|
964 |
gFreeList = temp + 1; |
|
965 |
Thread::muxRelease (&ListLock) ; |
|
966 |
TEVENT (Allocate block of monitors) ; |
|
967 |
} |
|
968 |
} |
|
969 |
||
970 |
// Place "m" on the caller's private per-thread omFreeList. |
|
971 |
// In practice there's no need to clamp or limit the number of |
|
972 |
// monitors on a thread's omFreeList as the only time we'll call |
|
973 |
// omRelease is to return a monitor to the free list after a CAS |
|
974 |
// attempt failed. This doesn't allow unbounded #s of monitors to |
|
975 |
// accumulate on a thread's free list. |
|
976 |
// |
|
977 |
// In the future the usage of omRelease() might change and monitors |
|
978 |
// could migrate between free lists. In that case to avoid excessive |
|
979 |
// accumulation we could limit omCount to (omProvision*2), otherwise return |
|
980 |
// the objectMonitor to the global list. We should drain (return) in reasonable chunks. |
|
981 |
// That is, *not* one-at-a-time. |
|
982 |
||
983 |
||
5920
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changeset
|
984 |
void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) { |
1 | 985 |
guarantee (m->object() == NULL, "invariant") ; |
5920
8fdbb85e62d3
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changeset
|
986 |
|
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
987 |
// Remove from omInUseList |
8fdbb85e62d3
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diff
changeset
|
988 |
if (MonitorInUseLists && fromPerThreadAlloc) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
989 |
ObjectMonitor* curmidinuse = NULL; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
990 |
for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; ) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
991 |
if (m == mid) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
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diff
changeset
|
992 |
// extract from per-thread in-use-list |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
993 |
if (mid == Self->omInUseList) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
994 |
Self->omInUseList = mid->FreeNext; |
8fdbb85e62d3
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changeset
|
995 |
} else if (curmidinuse != NULL) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
996 |
curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
8fdbb85e62d3
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parents:
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diff
changeset
|
997 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
998 |
Self->omInUseCount --; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
999 |
// verifyInUse(Self); |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1000 |
break; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1001 |
} else { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
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diff
changeset
|
1002 |
curmidinuse = mid; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1003 |
mid = mid->FreeNext; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1004 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1005 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1006 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1007 |
|
8fdbb85e62d3
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|
1008 |
// FreeNext is used for both onInUseList and omFreeList, so clear old before setting new |
8fdbb85e62d3
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|
1009 |
m->FreeNext = Self->omFreeList ; |
8fdbb85e62d3
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|
1010 |
Self->omFreeList = m ; |
8fdbb85e62d3
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|
1011 |
Self->omFreeCount ++ ; |
1 | 1012 |
} |
1013 |
||
1014 |
// Return the monitors of a moribund thread's local free list to |
|
1015 |
// the global free list. Typically a thread calls omFlush() when |
|
1016 |
// it's dying. We could also consider having the VM thread steal |
|
1017 |
// monitors from threads that have not run java code over a few |
|
1018 |
// consecutive STW safepoints. Relatedly, we might decay |
|
1019 |
// omFreeProvision at STW safepoints. |
|
1020 |
// |
|
5920
8fdbb85e62d3
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|
1021 |
// Also return the monitors of a moribund thread"s omInUseList to |
8fdbb85e62d3
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|
1022 |
// a global gOmInUseList under the global list lock so these |
8fdbb85e62d3
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|
1023 |
// will continue to be scanned. |
8fdbb85e62d3
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|
1024 |
// |
1 | 1025 |
// We currently call omFlush() from the Thread:: dtor _after the thread |
1026 |
// has been excised from the thread list and is no longer a mutator. |
|
1027 |
// That means that omFlush() can run concurrently with a safepoint and |
|
1028 |
// the scavenge operator. Calling omFlush() from JavaThread::exit() might |
|
1029 |
// be a better choice as we could safely reason that that the JVM is |
|
1030 |
// not at a safepoint at the time of the call, and thus there could |
|
1031 |
// be not inopportune interleavings between omFlush() and the scavenge |
|
1032 |
// operator. |
|
1033 |
||
1034 |
void ObjectSynchronizer::omFlush (Thread * Self) { |
|
1035 |
ObjectMonitor * List = Self->omFreeList ; // Null-terminated SLL |
|
1036 |
Self->omFreeList = NULL ; |
|
1037 |
ObjectMonitor * Tail = NULL ; |
|
5710 | 1038 |
int Tally = 0; |
5920
8fdbb85e62d3
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changeset
|
1039 |
if (List != NULL) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1040 |
ObjectMonitor * s ; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1041 |
for (s = List ; s != NULL ; s = s->FreeNext) { |
8fdbb85e62d3
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parents:
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changeset
|
1042 |
Tally ++ ; |
8fdbb85e62d3
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changeset
|
1043 |
Tail = s ; |
8fdbb85e62d3
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|
1044 |
guarantee (s->object() == NULL, "invariant") ; |
8fdbb85e62d3
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|
1045 |
guarantee (!s->is_busy(), "invariant") ; |
8fdbb85e62d3
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|
1046 |
s->set_owner (NULL) ; // redundant but good hygiene |
8fdbb85e62d3
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|
1047 |
TEVENT (omFlush - Move one) ; |
8fdbb85e62d3
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|
1048 |
} |
8fdbb85e62d3
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|
1049 |
guarantee (Tail != NULL && List != NULL, "invariant") ; |
1 | 1050 |
} |
1051 |
||
5920
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|
1052 |
ObjectMonitor * InUseList = Self->omInUseList; |
8fdbb85e62d3
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diff
changeset
|
1053 |
ObjectMonitor * InUseTail = NULL ; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1054 |
int InUseTally = 0; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
5712
diff
changeset
|
1055 |
if (InUseList != NULL) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
5712
diff
changeset
|
1056 |
Self->omInUseList = NULL; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1057 |
ObjectMonitor *curom; |
8fdbb85e62d3
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changeset
|
1058 |
for (curom = InUseList; curom != NULL; curom = curom->FreeNext) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
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diff
changeset
|
1059 |
InUseTail = curom; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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parents:
5712
diff
changeset
|
1060 |
InUseTally++; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1061 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1062 |
// TODO debug |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1063 |
assert(Self->omInUseCount == InUseTally, "inuse count off"); |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1064 |
Self->omInUseCount = 0; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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|
1065 |
guarantee (InUseTail != NULL && InUseList != NULL, "invariant"); |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1066 |
} |
8fdbb85e62d3
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changeset
|
1067 |
|
1 | 1068 |
Thread::muxAcquire (&ListLock, "omFlush") ; |
5920
8fdbb85e62d3
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changeset
|
1069 |
if (Tail != NULL) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1070 |
Tail->FreeNext = gFreeList ; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1071 |
gFreeList = List ; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1072 |
MonitorFreeCount += Tally; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1073 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1074 |
|
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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diff
changeset
|
1075 |
if (InUseTail != NULL) { |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1076 |
InUseTail->FreeNext = gOmInUseList; |
8fdbb85e62d3
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|
1077 |
gOmInUseList = InUseList; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1078 |
gOmInUseCount += InUseTally; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
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changeset
|
1079 |
} |
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|
1080 |
|
1 | 1081 |
Thread::muxRelease (&ListLock) ; |
1082 |
TEVENT (omFlush) ; |
|
1083 |
} |
|
1084 |
||
1085 |
||
1086 |
// Get the next block in the block list. |
|
1087 |
static inline ObjectMonitor* next(ObjectMonitor* block) { |
|
1088 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
1089 |
block = block->FreeNext ; |
|
1090 |
assert(block == NULL || block->object() == CHAINMARKER, "must be a block header"); |
|
1091 |
return block; |
|
1092 |
} |
|
1093 |
||
1094 |
// Fast path code shared by multiple functions |
|
1095 |
ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) { |
|
1096 |
markOop mark = obj->mark(); |
|
1097 |
if (mark->has_monitor()) { |
|
1098 |
assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid"); |
|
1099 |
assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header"); |
|
1100 |
return mark->monitor(); |
|
1101 |
} |
|
1102 |
return ObjectSynchronizer::inflate(Thread::current(), obj); |
|
1103 |
} |
|
1104 |
||
1105 |
// Note that we could encounter some performance loss through false-sharing as |
|
1106 |
// multiple locks occupy the same $ line. Padding might be appropriate. |
|
1107 |
||
1108 |
#define NINFLATIONLOCKS 256 |
|
1109 |
static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ; |
|
1110 |
||
1111 |
static markOop ReadStableMark (oop obj) { |
|
1112 |
markOop mark = obj->mark() ; |
|
1113 |
if (!mark->is_being_inflated()) { |
|
1114 |
return mark ; // normal fast-path return |
|
1115 |
} |
|
1116 |
||
1117 |
int its = 0 ; |
|
1118 |
for (;;) { |
|
1119 |
markOop mark = obj->mark() ; |
|
1120 |
if (!mark->is_being_inflated()) { |
|
1121 |
return mark ; // normal fast-path return |
|
1122 |
} |
|
1123 |
||
1124 |
// The object is being inflated by some other thread. |
|
1125 |
// The caller of ReadStableMark() must wait for inflation to complete. |
|
1126 |
// Avoid live-lock |
|
1127 |
// TODO: consider calling SafepointSynchronize::do_call_back() while |
|
1128 |
// spinning to see if there's a safepoint pending. If so, immediately |
|
1129 |
// yielding or blocking would be appropriate. Avoid spinning while |
|
1130 |
// there is a safepoint pending. |
|
1131 |
// TODO: add inflation contention performance counters. |
|
1132 |
// TODO: restrict the aggregate number of spinners. |
|
1133 |
||
1134 |
++its ; |
|
1135 |
if (its > 10000 || !os::is_MP()) { |
|
1136 |
if (its & 1) { |
|
1137 |
os::NakedYield() ; |
|
1138 |
TEVENT (Inflate: INFLATING - yield) ; |
|
1139 |
} else { |
|
1140 |
// Note that the following code attenuates the livelock problem but is not |
|
1141 |
// a complete remedy. A more complete solution would require that the inflating |
|
1142 |
// thread hold the associated inflation lock. The following code simply restricts |
|
1143 |
// the number of spinners to at most one. We'll have N-2 threads blocked |
|
1144 |
// on the inflationlock, 1 thread holding the inflation lock and using |
|
1145 |
// a yield/park strategy, and 1 thread in the midst of inflation. |
|
1146 |
// A more refined approach would be to change the encoding of INFLATING |
|
1147 |
// to allow encapsulation of a native thread pointer. Threads waiting for |
|
1148 |
// inflation to complete would use CAS to push themselves onto a singly linked |
|
1149 |
// list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag |
|
1150 |
// and calling park(). When inflation was complete the thread that accomplished inflation |
|
1151 |
// would detach the list and set the markword to inflated with a single CAS and |
|
1152 |
// then for each thread on the list, set the flag and unpark() the thread. |
|
1153 |
// This is conceptually similar to muxAcquire-muxRelease, except that muxRelease |
|
1154 |
// wakes at most one thread whereas we need to wake the entire list. |
|
1155 |
int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ; |
|
1156 |
int YieldThenBlock = 0 ; |
|
1157 |
assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ; |
|
1158 |
assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ; |
|
1159 |
Thread::muxAcquire (InflationLocks + ix, "InflationLock") ; |
|
1160 |
while (obj->mark() == markOopDesc::INFLATING()) { |
|
1161 |
// Beware: NakedYield() is advisory and has almost no effect on some platforms |
|
1162 |
// so we periodically call Self->_ParkEvent->park(1). |
|
1163 |
// We use a mixed spin/yield/block mechanism. |
|
1164 |
if ((YieldThenBlock++) >= 16) { |
|
1165 |
Thread::current()->_ParkEvent->park(1) ; |
|
1166 |
} else { |
|
1167 |
os::NakedYield() ; |
|
1168 |
} |
|
1169 |
} |
|
1170 |
Thread::muxRelease (InflationLocks + ix ) ; |
|
1171 |
TEVENT (Inflate: INFLATING - yield/park) ; |
|
1172 |
} |
|
1173 |
} else { |
|
1174 |
SpinPause() ; // SMP-polite spinning |
|
1175 |
} |
|
1176 |
} |
|
1177 |
} |
|
1178 |
||
1179 |
ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) { |
|
1180 |
// Inflate mutates the heap ... |
|
1181 |
// Relaxing assertion for bug 6320749. |
|
1182 |
assert (Universe::verify_in_progress() || |
|
1183 |
!SafepointSynchronize::is_at_safepoint(), "invariant") ; |
|
1184 |
||
1185 |
for (;;) { |
|
1186 |
const markOop mark = object->mark() ; |
|
1187 |
assert (!mark->has_bias_pattern(), "invariant") ; |
|
1188 |
||
1189 |
// The mark can be in one of the following states: |
|
1190 |
// * Inflated - just return |
|
1191 |
// * Stack-locked - coerce it to inflated |
|
1192 |
// * INFLATING - busy wait for conversion to complete |
|
1193 |
// * Neutral - aggressively inflate the object. |
|
1194 |
// * BIASED - Illegal. We should never see this |
|
1195 |
||
1196 |
// CASE: inflated |
|
1197 |
if (mark->has_monitor()) { |
|
1198 |
ObjectMonitor * inf = mark->monitor() ; |
|
1199 |
assert (inf->header()->is_neutral(), "invariant"); |
|
1200 |
assert (inf->object() == object, "invariant") ; |
|
1201 |
assert (ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid"); |
|
1202 |
return inf ; |
|
1203 |
} |
|
1204 |
||
1205 |
// CASE: inflation in progress - inflating over a stack-lock. |
|
1206 |
// Some other thread is converting from stack-locked to inflated. |
|
1207 |
// Only that thread can complete inflation -- other threads must wait. |
|
1208 |
// The INFLATING value is transient. |
|
1209 |
// Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. |
|
1210 |
// We could always eliminate polling by parking the thread on some auxiliary list. |
|
1211 |
if (mark == markOopDesc::INFLATING()) { |
|
1212 |
TEVENT (Inflate: spin while INFLATING) ; |
|
1213 |
ReadStableMark(object) ; |
|
1214 |
continue ; |
|
1215 |
} |
|
1216 |
||
1217 |
// CASE: stack-locked |
|
1218 |
// Could be stack-locked either by this thread or by some other thread. |
|
1219 |
// |
|
1220 |
// Note that we allocate the objectmonitor speculatively, _before_ attempting |
|
1221 |
// to install INFLATING into the mark word. We originally installed INFLATING, |
|
1222 |
// allocated the objectmonitor, and then finally STed the address of the |
|
1223 |
// objectmonitor into the mark. This was correct, but artificially lengthened |
|
1224 |
// the interval in which INFLATED appeared in the mark, thus increasing |
|
1225 |
// the odds of inflation contention. |
|
1226 |
// |
|
1227 |
// We now use per-thread private objectmonitor free lists. |
|
1228 |
// These list are reprovisioned from the global free list outside the |
|
1229 |
// critical INFLATING...ST interval. A thread can transfer |
|
1230 |
// multiple objectmonitors en-mass from the global free list to its local free list. |
|
1231 |
// This reduces coherency traffic and lock contention on the global free list. |
|
1232 |
// Using such local free lists, it doesn't matter if the omAlloc() call appears |
|
1233 |
// before or after the CAS(INFLATING) operation. |
|
1234 |
// See the comments in omAlloc(). |
|
1235 |
||
1236 |
if (mark->has_locker()) { |
|
1237 |
ObjectMonitor * m = omAlloc (Self) ; |
|
1238 |
// Optimistically prepare the objectmonitor - anticipate successful CAS |
|
1239 |
// We do this before the CAS in order to minimize the length of time |
|
1240 |
// in which INFLATING appears in the mark. |
|
1241 |
m->Recycle(); |
|
1242 |
m->_Responsible = NULL ; |
|
1243 |
m->OwnerIsThread = 0 ; |
|
1244 |
m->_recursions = 0 ; |
|
1245 |
m->_SpinDuration = Knob_SpinLimit ; // Consider: maintain by type/class |
|
1246 |
||
1247 |
markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ; |
|
1248 |
if (cmp != mark) { |
|
5920
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diff
changeset
|
1249 |
omRelease (Self, m, true) ; |
1 | 1250 |
continue ; // Interference -- just retry |
1251 |
} |
|
1252 |
||
1253 |
// We've successfully installed INFLATING (0) into the mark-word. |
|
1254 |
// This is the only case where 0 will appear in a mark-work. |
|
1255 |
// Only the singular thread that successfully swings the mark-word |
|
1256 |
// to 0 can perform (or more precisely, complete) inflation. |
|
1257 |
// |
|
1258 |
// Why do we CAS a 0 into the mark-word instead of just CASing the |
|
1259 |
// mark-word from the stack-locked value directly to the new inflated state? |
|
1260 |
// Consider what happens when a thread unlocks a stack-locked object. |
|
1261 |
// It attempts to use CAS to swing the displaced header value from the |
|
1262 |
// on-stack basiclock back into the object header. Recall also that the |
|
1263 |
// header value (hashcode, etc) can reside in (a) the object header, or |
|
1264 |
// (b) a displaced header associated with the stack-lock, or (c) a displaced |
|
1265 |
// header in an objectMonitor. The inflate() routine must copy the header |
|
1266 |
// value from the basiclock on the owner's stack to the objectMonitor, all |
|
1267 |
// the while preserving the hashCode stability invariants. If the owner |
|
1268 |
// decides to release the lock while the value is 0, the unlock will fail |
|
1269 |
// and control will eventually pass from slow_exit() to inflate. The owner |
|
1270 |
// will then spin, waiting for the 0 value to disappear. Put another way, |
|
1271 |
// the 0 causes the owner to stall if the owner happens to try to |
|
1272 |
// drop the lock (restoring the header from the basiclock to the object) |
|
1273 |
// while inflation is in-progress. This protocol avoids races that might |
|
1274 |
// would otherwise permit hashCode values to change or "flicker" for an object. |
|
1275 |
// Critically, while object->mark is 0 mark->displaced_mark_helper() is stable. |
|
1276 |
// 0 serves as a "BUSY" inflate-in-progress indicator. |
|
1277 |
||
1278 |
||
1279 |
// fetch the displaced mark from the owner's stack. |
|
1280 |
// The owner can't die or unwind past the lock while our INFLATING |
|
1281 |
// object is in the mark. Furthermore the owner can't complete |
|
1282 |
// an unlock on the object, either. |
|
1283 |
markOop dmw = mark->displaced_mark_helper() ; |
|
1284 |
assert (dmw->is_neutral(), "invariant") ; |
|
1285 |
||
1286 |
// Setup monitor fields to proper values -- prepare the monitor |
|
1287 |
m->set_header(dmw) ; |
|
1288 |
||
1289 |
// Optimization: if the mark->locker stack address is associated |
|
1290 |
// with this thread we could simply set m->_owner = Self and |
|
2526
39a58a50be35
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parents:
2105
diff
changeset
|
1291 |
// m->OwnerIsThread = 1. Note that a thread can inflate an object |
1 | 1292 |
// that it has stack-locked -- as might happen in wait() -- directly |
1293 |
// with CAS. That is, we can avoid the xchg-NULL .... ST idiom. |
|
2526
39a58a50be35
6699669: Hotspot server leaves synchronized block with monitor in bad state
xlu
parents:
2105
diff
changeset
|
1294 |
m->set_owner(mark->locker()); |
1 | 1295 |
m->set_object(object); |
1296 |
// TODO-FIXME: assert BasicLock->dhw != 0. |
|
1297 |
||
1298 |
// Must preserve store ordering. The monitor state must |
|
1299 |
// be stable at the time of publishing the monitor address. |
|
1300 |
guarantee (object->mark() == markOopDesc::INFLATING(), "invariant") ; |
|
1301 |
object->release_set_mark(markOopDesc::encode(m)); |
|
1302 |
||
1303 |
// Hopefully the performance counters are allocated on distinct cache lines |
|
1304 |
// to avoid false sharing on MP systems ... |
|
1305 |
if (_sync_Inflations != NULL) _sync_Inflations->inc() ; |
|
1306 |
TEVENT(Inflate: overwrite stacklock) ; |
|
1307 |
if (TraceMonitorInflation) { |
|
1308 |
if (object->is_instance()) { |
|
1309 |
ResourceMark rm; |
|
1310 |
tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
|
1311 |
(intptr_t) object, (intptr_t) object->mark(), |
|
1312 |
Klass::cast(object->klass())->external_name()); |
|
1313 |
} |
|
1314 |
} |
|
1315 |
return m ; |
|
1316 |
} |
|
1317 |
||
1318 |
// CASE: neutral |
|
1319 |
// TODO-FIXME: for entry we currently inflate and then try to CAS _owner. |
|
1320 |
// If we know we're inflating for entry it's better to inflate by swinging a |
|
1321 |
// pre-locked objectMonitor pointer into the object header. A successful |
|
1322 |
// CAS inflates the object *and* confers ownership to the inflating thread. |
|
1323 |
// In the current implementation we use a 2-step mechanism where we CAS() |
|
1324 |
// to inflate and then CAS() again to try to swing _owner from NULL to Self. |
|
1325 |
// An inflateTry() method that we could call from fast_enter() and slow_enter() |
|
1326 |
// would be useful. |
|
1327 |
||
1328 |
assert (mark->is_neutral(), "invariant"); |
|
1329 |
ObjectMonitor * m = omAlloc (Self) ; |
|
1330 |
// prepare m for installation - set monitor to initial state |
|
1331 |
m->Recycle(); |
|
1332 |
m->set_header(mark); |
|
1333 |
m->set_owner(NULL); |
|
1334 |
m->set_object(object); |
|
1335 |
m->OwnerIsThread = 1 ; |
|
1336 |
m->_recursions = 0 ; |
|
1337 |
m->_Responsible = NULL ; |
|
1338 |
m->_SpinDuration = Knob_SpinLimit ; // consider: keep metastats by type/class |
|
1339 |
||
1340 |
if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) { |
|
1341 |
m->set_object (NULL) ; |
|
1342 |
m->set_owner (NULL) ; |
|
1343 |
m->OwnerIsThread = 0 ; |
|
1344 |
m->Recycle() ; |
|
5920
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5712
diff
changeset
|
1345 |
omRelease (Self, m, true) ; |
1 | 1346 |
m = NULL ; |
1347 |
continue ; |
|
1348 |
// interference - the markword changed - just retry. |
|
1349 |
// The state-transitions are one-way, so there's no chance of |
|
1350 |
// live-lock -- "Inflated" is an absorbing state. |
|
1351 |
} |
|
1352 |
||
1353 |
// Hopefully the performance counters are allocated on distinct |
|
1354 |
// cache lines to avoid false sharing on MP systems ... |
|
1355 |
if (_sync_Inflations != NULL) _sync_Inflations->inc() ; |
|
1356 |
TEVENT(Inflate: overwrite neutral) ; |
|
1357 |
if (TraceMonitorInflation) { |
|
1358 |
if (object->is_instance()) { |
|
1359 |
ResourceMark rm; |
|
1360 |
tty->print_cr("Inflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
|
1361 |
(intptr_t) object, (intptr_t) object->mark(), |
|
1362 |
Klass::cast(object->klass())->external_name()); |
|
1363 |
} |
|
1364 |
} |
|
1365 |
return m ; |
|
1366 |
} |
|
1367 |
} |
|
1368 |
||
1369 |
||
1370 |
// This the fast monitor enter. The interpreter and compiler use |
|
1371 |
// some assembly copies of this code. Make sure update those code |
|
1372 |
// if the following function is changed. The implementation is |
|
1373 |
// extremely sensitive to race condition. Be careful. |
|
1374 |
||
1375 |
void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) { |
|
1376 |
if (UseBiasedLocking) { |
|
1377 |
if (!SafepointSynchronize::is_at_safepoint()) { |
|
1378 |
BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD); |
|
1379 |
if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) { |
|
1380 |
return; |
|
1381 |
} |
|
1382 |
} else { |
|
1383 |
assert(!attempt_rebias, "can not rebias toward VM thread"); |
|
1384 |
BiasedLocking::revoke_at_safepoint(obj); |
|
1385 |
} |
|
1386 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
2526
39a58a50be35
6699669: Hotspot server leaves synchronized block with monitor in bad state
xlu
parents:
2105
diff
changeset
|
1387 |
} |
39a58a50be35
6699669: Hotspot server leaves synchronized block with monitor in bad state
xlu
parents:
2105
diff
changeset
|
1388 |
|
39a58a50be35
6699669: Hotspot server leaves synchronized block with monitor in bad state
xlu
parents:
2105
diff
changeset
|
1389 |
slow_enter (obj, lock, THREAD) ; |
1 | 1390 |
} |
1391 |
||
1392 |
void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) { |
|
1393 |
assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here"); |
|
1394 |
// if displaced header is null, the previous enter is recursive enter, no-op |
|
1395 |
markOop dhw = lock->displaced_header(); |
|
1396 |
markOop mark ; |
|
1397 |
if (dhw == NULL) { |
|
1398 |
// Recursive stack-lock. |
|
1399 |
// Diagnostics -- Could be: stack-locked, inflating, inflated. |
|
1400 |
mark = object->mark() ; |
|
1401 |
assert (!mark->is_neutral(), "invariant") ; |
|
1402 |
if (mark->has_locker() && mark != markOopDesc::INFLATING()) { |
|
1403 |
assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ; |
|
1404 |
} |
|
1405 |
if (mark->has_monitor()) { |
|
1406 |
ObjectMonitor * m = mark->monitor() ; |
|
1407 |
assert(((oop)(m->object()))->mark() == mark, "invariant") ; |
|
1408 |
assert(m->is_entered(THREAD), "invariant") ; |
|
1409 |
} |
|
1410 |
return ; |
|
1411 |
} |
|
1412 |
||
1413 |
mark = object->mark() ; |
|
1414 |
||
1415 |
// If the object is stack-locked by the current thread, try to |
|
1416 |
// swing the displaced header from the box back to the mark. |
|
1417 |
if (mark == (markOop) lock) { |
|
1418 |
assert (dhw->is_neutral(), "invariant") ; |
|
1419 |
if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) { |
|
1420 |
TEVENT (fast_exit: release stacklock) ; |
|
1421 |
return; |
|
1422 |
} |
|
1423 |
} |
|
1424 |
||
1425 |
ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ; |
|
1426 |
} |
|
1427 |
||
1428 |
// This routine is used to handle interpreter/compiler slow case |
|
1429 |
// We don't need to use fast path here, because it must have been |
|
1430 |
// failed in the interpreter/compiler code. |
|
1431 |
void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) { |
|
1432 |
markOop mark = obj->mark(); |
|
1433 |
assert(!mark->has_bias_pattern(), "should not see bias pattern here"); |
|
1434 |
||
1435 |
if (mark->is_neutral()) { |
|
1436 |
// Anticipate successful CAS -- the ST of the displaced mark must |
|
1437 |
// be visible <= the ST performed by the CAS. |
|
1438 |
lock->set_displaced_header(mark); |
|
1439 |
if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) { |
|
1440 |
TEVENT (slow_enter: release stacklock) ; |
|
1441 |
return ; |
|
1442 |
} |
|
1443 |
// Fall through to inflate() ... |
|
1444 |
} else |
|
1445 |
if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
|
1446 |
assert(lock != mark->locker(), "must not re-lock the same lock"); |
|
1447 |
assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock"); |
|
1448 |
lock->set_displaced_header(NULL); |
|
1449 |
return; |
|
1450 |
} |
|
1451 |
||
1452 |
#if 0 |
|
1453 |
// The following optimization isn't particularly useful. |
|
1454 |
if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) { |
|
1455 |
lock->set_displaced_header (NULL) ; |
|
1456 |
return ; |
|
1457 |
} |
|
1458 |
#endif |
|
1459 |
||
1460 |
// The object header will never be displaced to this lock, |
|
1461 |
// so it does not matter what the value is, except that it |
|
1462 |
// must be non-zero to avoid looking like a re-entrant lock, |
|
1463 |
// and must not look locked either. |
|
1464 |
lock->set_displaced_header(markOopDesc::unused_mark()); |
|
1465 |
ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); |
|
1466 |
} |
|
1467 |
||
1468 |
// This routine is used to handle interpreter/compiler slow case |
|
1469 |
// We don't need to use fast path here, because it must have |
|
1470 |
// failed in the interpreter/compiler code. Simply use the heavy |
|
1471 |
// weight monitor should be ok, unless someone find otherwise. |
|
1472 |
void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) { |
|
1473 |
fast_exit (object, lock, THREAD) ; |
|
1474 |
} |
|
1475 |
||
1476 |
// NOTE: must use heavy weight monitor to handle jni monitor enter |
|
1477 |
void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter |
|
1478 |
// the current locking is from JNI instead of Java code |
|
1479 |
TEVENT (jni_enter) ; |
|
1480 |
if (UseBiasedLocking) { |
|
1481 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1482 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1483 |
} |
|
1484 |
THREAD->set_current_pending_monitor_is_from_java(false); |
|
1485 |
ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD); |
|
1486 |
THREAD->set_current_pending_monitor_is_from_java(true); |
|
1487 |
} |
|
1488 |
||
1489 |
// NOTE: must use heavy weight monitor to handle jni monitor enter |
|
1490 |
bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) { |
|
1491 |
if (UseBiasedLocking) { |
|
1492 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1493 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1494 |
} |
|
1495 |
||
1496 |
ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj()); |
|
1497 |
return monitor->try_enter(THREAD); |
|
1498 |
} |
|
1499 |
||
1500 |
||
1501 |
// NOTE: must use heavy weight monitor to handle jni monitor exit |
|
1502 |
void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) { |
|
1503 |
TEVENT (jni_exit) ; |
|
1504 |
if (UseBiasedLocking) { |
|
1505 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1506 |
} |
|
1507 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1508 |
||
1509 |
ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj); |
|
1510 |
// If this thread has locked the object, exit the monitor. Note: can't use |
|
1511 |
// monitor->check(CHECK); must exit even if an exception is pending. |
|
1512 |
if (monitor->check(THREAD)) { |
|
1513 |
monitor->exit(THREAD); |
|
1514 |
} |
|
1515 |
} |
|
1516 |
||
1517 |
// complete_exit()/reenter() are used to wait on a nested lock |
|
1518 |
// i.e. to give up an outer lock completely and then re-enter |
|
1519 |
// Used when holding nested locks - lock acquisition order: lock1 then lock2 |
|
1520 |
// 1) complete_exit lock1 - saving recursion count |
|
1521 |
// 2) wait on lock2 |
|
1522 |
// 3) when notified on lock2, unlock lock2 |
|
1523 |
// 4) reenter lock1 with original recursion count |
|
1524 |
// 5) lock lock2 |
|
1525 |
// NOTE: must use heavy weight monitor to handle complete_exit/reenter() |
|
1526 |
intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) { |
|
1527 |
TEVENT (complete_exit) ; |
|
1528 |
if (UseBiasedLocking) { |
|
1529 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1530 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1531 |
} |
|
1532 |
||
1533 |
ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
|
1534 |
||
1535 |
return monitor->complete_exit(THREAD); |
|
1536 |
} |
|
1537 |
||
1538 |
// NOTE: must use heavy weight monitor to handle complete_exit/reenter() |
|
1539 |
void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) { |
|
1540 |
TEVENT (reenter) ; |
|
1541 |
if (UseBiasedLocking) { |
|
1542 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1543 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1544 |
} |
|
1545 |
||
1546 |
ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
|
1547 |
||
1548 |
monitor->reenter(recursion, THREAD); |
|
1549 |
} |
|
1550 |
||
1551 |
// This exists only as a workaround of dtrace bug 6254741 |
|
1552 |
int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { |
|
1553 |
DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); |
|
1554 |
return 0; |
|
1555 |
} |
|
1556 |
||
1557 |
// NOTE: must use heavy weight monitor to handle wait() |
|
1558 |
void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { |
|
1559 |
if (UseBiasedLocking) { |
|
1560 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1561 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1562 |
} |
|
1563 |
if (millis < 0) { |
|
1564 |
TEVENT (wait - throw IAX) ; |
|
1565 |
THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
|
1566 |
} |
|
1567 |
ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj()); |
|
1568 |
DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis); |
|
1569 |
monitor->wait(millis, true, THREAD); |
|
1570 |
||
1571 |
/* This dummy call is in place to get around dtrace bug 6254741. Once |
|
1572 |
that's fixed we can uncomment the following line and remove the call */ |
|
1573 |
// DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); |
|
1574 |
dtrace_waited_probe(monitor, obj, THREAD); |
|
1575 |
} |
|
1576 |
||
1577 |
void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) { |
|
1578 |
if (UseBiasedLocking) { |
|
1579 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1580 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1581 |
} |
|
1582 |
if (millis < 0) { |
|
1583 |
TEVENT (wait - throw IAX) ; |
|
1584 |
THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); |
|
1585 |
} |
|
1586 |
ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ; |
|
1587 |
} |
|
1588 |
||
1589 |
void ObjectSynchronizer::notify(Handle obj, TRAPS) { |
|
1590 |
if (UseBiasedLocking) { |
|
1591 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1592 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1593 |
} |
|
1594 |
||
1595 |
markOop mark = obj->mark(); |
|
1596 |
if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
|
1597 |
return; |
|
1598 |
} |
|
1599 |
ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD); |
|
1600 |
} |
|
1601 |
||
1602 |
// NOTE: see comment of notify() |
|
1603 |
void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { |
|
1604 |
if (UseBiasedLocking) { |
|
1605 |
BiasedLocking::revoke_and_rebias(obj, false, THREAD); |
|
1606 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1607 |
} |
|
1608 |
||
1609 |
markOop mark = obj->mark(); |
|
1610 |
if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) { |
|
1611 |
return; |
|
1612 |
} |
|
1613 |
ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD); |
|
1614 |
} |
|
1615 |
||
1616 |
intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) { |
|
1617 |
if (UseBiasedLocking) { |
|
1618 |
// NOTE: many places throughout the JVM do not expect a safepoint |
|
1619 |
// to be taken here, in particular most operations on perm gen |
|
1620 |
// objects. However, we only ever bias Java instances and all of |
|
1621 |
// the call sites of identity_hash that might revoke biases have |
|
1622 |
// been checked to make sure they can handle a safepoint. The |
|
1623 |
// added check of the bias pattern is to avoid useless calls to |
|
1624 |
// thread-local storage. |
|
1625 |
if (obj->mark()->has_bias_pattern()) { |
|
1626 |
// Box and unbox the raw reference just in case we cause a STW safepoint. |
|
1627 |
Handle hobj (Self, obj) ; |
|
1628 |
// Relaxing assertion for bug 6320749. |
|
1629 |
assert (Universe::verify_in_progress() || |
|
1630 |
!SafepointSynchronize::is_at_safepoint(), |
|
1631 |
"biases should not be seen by VM thread here"); |
|
1632 |
BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current()); |
|
1633 |
obj = hobj() ; |
|
1634 |
assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1635 |
} |
|
1636 |
} |
|
1637 |
||
1638 |
// hashCode() is a heap mutator ... |
|
1639 |
// Relaxing assertion for bug 6320749. |
|
1640 |
assert (Universe::verify_in_progress() || |
|
1641 |
!SafepointSynchronize::is_at_safepoint(), "invariant") ; |
|
1642 |
assert (Universe::verify_in_progress() || |
|
1643 |
Self->is_Java_thread() , "invariant") ; |
|
1644 |
assert (Universe::verify_in_progress() || |
|
1645 |
((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; |
|
1646 |
||
1647 |
ObjectMonitor* monitor = NULL; |
|
1648 |
markOop temp, test; |
|
1649 |
intptr_t hash; |
|
1650 |
markOop mark = ReadStableMark (obj); |
|
1651 |
||
1652 |
// object should remain ineligible for biased locking |
|
1653 |
assert (!mark->has_bias_pattern(), "invariant") ; |
|
1654 |
||
1655 |
if (mark->is_neutral()) { |
|
1656 |
hash = mark->hash(); // this is a normal header |
|
1657 |
if (hash) { // if it has hash, just return it |
|
1658 |
return hash; |
|
1659 |
} |
|
1660 |
hash = get_next_hash(Self, obj); // allocate a new hash code |
|
1661 |
temp = mark->copy_set_hash(hash); // merge the hash code into header |
|
1662 |
// use (machine word version) atomic operation to install the hash |
|
1663 |
test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark); |
|
1664 |
if (test == mark) { |
|
1665 |
return hash; |
|
1666 |
} |
|
1667 |
// If atomic operation failed, we must inflate the header |
|
1668 |
// into heavy weight monitor. We could add more code here |
|
1669 |
// for fast path, but it does not worth the complexity. |
|
1670 |
} else if (mark->has_monitor()) { |
|
1671 |
monitor = mark->monitor(); |
|
1672 |
temp = monitor->header(); |
|
1673 |
assert (temp->is_neutral(), "invariant") ; |
|
1674 |
hash = temp->hash(); |
|
1675 |
if (hash) { |
|
1676 |
return hash; |
|
1677 |
} |
|
1678 |
// Skip to the following code to reduce code size |
|
1679 |
} else if (Self->is_lock_owned((address)mark->locker())) { |
|
1680 |
temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned |
|
1681 |
assert (temp->is_neutral(), "invariant") ; |
|
1682 |
hash = temp->hash(); // by current thread, check if the displaced |
|
1683 |
if (hash) { // header contains hash code |
|
1684 |
return hash; |
|
1685 |
} |
|
1686 |
// WARNING: |
|
1687 |
// The displaced header is strictly immutable. |
|
1688 |
// It can NOT be changed in ANY cases. So we have |
|
1689 |
// to inflate the header into heavyweight monitor |
|
1690 |
// even the current thread owns the lock. The reason |
|
1691 |
// is the BasicLock (stack slot) will be asynchronously |
|
1692 |
// read by other threads during the inflate() function. |
|
1693 |
// Any change to stack may not propagate to other threads |
|
1694 |
// correctly. |
|
1695 |
} |
|
1696 |
||
1697 |
// Inflate the monitor to set hash code |
|
1698 |
monitor = ObjectSynchronizer::inflate(Self, obj); |
|
1699 |
// Load displaced header and check it has hash code |
|
1700 |
mark = monitor->header(); |
|
1701 |
assert (mark->is_neutral(), "invariant") ; |
|
1702 |
hash = mark->hash(); |
|
1703 |
if (hash == 0) { |
|
1704 |
hash = get_next_hash(Self, obj); |
|
1705 |
temp = mark->copy_set_hash(hash); // merge hash code into header |
|
1706 |
assert (temp->is_neutral(), "invariant") ; |
|
1707 |
test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark); |
|
1708 |
if (test != mark) { |
|
1709 |
// The only update to the header in the monitor (outside GC) |
|
1710 |
// is install the hash code. If someone add new usage of |
|
1711 |
// displaced header, please update this code |
|
1712 |
hash = test->hash(); |
|
1713 |
assert (test->is_neutral(), "invariant") ; |
|
1714 |
assert (hash != 0, "Trivial unexpected object/monitor header usage."); |
|
1715 |
} |
|
1716 |
} |
|
1717 |
// We finally get the hash |
|
1718 |
return hash; |
|
1719 |
} |
|
1720 |
||
1721 |
// Deprecated -- use FastHashCode() instead. |
|
1722 |
||
1723 |
intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { |
|
1724 |
return FastHashCode (Thread::current(), obj()) ; |
|
1725 |
} |
|
1726 |
||
1727 |
bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread, |
|
1728 |
Handle h_obj) { |
|
1729 |
if (UseBiasedLocking) { |
|
1730 |
BiasedLocking::revoke_and_rebias(h_obj, false, thread); |
|
1731 |
assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1732 |
} |
|
1733 |
||
1734 |
assert(thread == JavaThread::current(), "Can only be called on current thread"); |
|
1735 |
oop obj = h_obj(); |
|
1736 |
||
1737 |
markOop mark = ReadStableMark (obj) ; |
|
1738 |
||
1739 |
// Uncontended case, header points to stack |
|
1740 |
if (mark->has_locker()) { |
|
1741 |
return thread->is_lock_owned((address)mark->locker()); |
|
1742 |
} |
|
1743 |
// Contended case, header points to ObjectMonitor (tagged pointer) |
|
1744 |
if (mark->has_monitor()) { |
|
1745 |
ObjectMonitor* monitor = mark->monitor(); |
|
1746 |
return monitor->is_entered(thread) != 0 ; |
|
1747 |
} |
|
1748 |
// Unlocked case, header in place |
|
1749 |
assert(mark->is_neutral(), "sanity check"); |
|
1750 |
return false; |
|
1751 |
} |
|
1752 |
||
1753 |
// Be aware of this method could revoke bias of the lock object. |
|
1754 |
// This method querys the ownership of the lock handle specified by 'h_obj'. |
|
1755 |
// If the current thread owns the lock, it returns owner_self. If no |
|
1756 |
// thread owns the lock, it returns owner_none. Otherwise, it will return |
|
1757 |
// ower_other. |
|
1758 |
ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership |
|
1759 |
(JavaThread *self, Handle h_obj) { |
|
1760 |
// The caller must beware this method can revoke bias, and |
|
1761 |
// revocation can result in a safepoint. |
|
1762 |
assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; |
|
1763 |
assert (self->thread_state() != _thread_blocked , "invariant") ; |
|
1764 |
||
1765 |
// Possible mark states: neutral, biased, stack-locked, inflated |
|
1766 |
||
1767 |
if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) { |
|
1768 |
// CASE: biased |
|
1769 |
BiasedLocking::revoke_and_rebias(h_obj, false, self); |
|
1770 |
assert(!h_obj->mark()->has_bias_pattern(), |
|
1771 |
"biases should be revoked by now"); |
|
1772 |
} |
|
1773 |
||
1774 |
assert(self == JavaThread::current(), "Can only be called on current thread"); |
|
1775 |
oop obj = h_obj(); |
|
1776 |
markOop mark = ReadStableMark (obj) ; |
|
1777 |
||
1778 |
// CASE: stack-locked. Mark points to a BasicLock on the owner's stack. |
|
1779 |
if (mark->has_locker()) { |
|
1780 |
return self->is_lock_owned((address)mark->locker()) ? |
|
1781 |
owner_self : owner_other; |
|
1782 |
} |
|
1783 |
||
1784 |
// CASE: inflated. Mark (tagged pointer) points to an objectMonitor. |
|
1785 |
// The Object:ObjectMonitor relationship is stable as long as we're |
|
1786 |
// not at a safepoint. |
|
1787 |
if (mark->has_monitor()) { |
|
1788 |
void * owner = mark->monitor()->_owner ; |
|
1789 |
if (owner == NULL) return owner_none ; |
|
1790 |
return (owner == self || |
|
1791 |
self->is_lock_owned((address)owner)) ? owner_self : owner_other; |
|
1792 |
} |
|
1793 |
||
1794 |
// CASE: neutral |
|
1795 |
assert(mark->is_neutral(), "sanity check"); |
|
1796 |
return owner_none ; // it's unlocked |
|
1797 |
} |
|
1798 |
||
1799 |
// FIXME: jvmti should call this |
|
1800 |
JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) { |
|
1801 |
if (UseBiasedLocking) { |
|
1802 |
if (SafepointSynchronize::is_at_safepoint()) { |
|
1803 |
BiasedLocking::revoke_at_safepoint(h_obj); |
|
1804 |
} else { |
|
1805 |
BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current()); |
|
1806 |
} |
|
1807 |
assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now"); |
|
1808 |
} |
|
1809 |
||
1810 |
oop obj = h_obj(); |
|
1811 |
address owner = NULL; |
|
1812 |
||
1813 |
markOop mark = ReadStableMark (obj) ; |
|
1814 |
||
1815 |
// Uncontended case, header points to stack |
|
1816 |
if (mark->has_locker()) { |
|
1817 |
owner = (address) mark->locker(); |
|
1818 |
} |
|
1819 |
||
1820 |
// Contended case, header points to ObjectMonitor (tagged pointer) |
|
1821 |
if (mark->has_monitor()) { |
|
1822 |
ObjectMonitor* monitor = mark->monitor(); |
|
1823 |
assert(monitor != NULL, "monitor should be non-null"); |
|
1824 |
owner = (address) monitor->owner(); |
|
1825 |
} |
|
1826 |
||
1827 |
if (owner != NULL) { |
|
1828 |
return Threads::owning_thread_from_monitor_owner(owner, doLock); |
|
1829 |
} |
|
1830 |
||
1831 |
// Unlocked case, header in place |
|
1832 |
// Cannot have assertion since this object may have been |
|
1833 |
// locked by another thread when reaching here. |
|
1834 |
// assert(mark->is_neutral(), "sanity check"); |
|
1835 |
||
1836 |
return NULL; |
|
1837 |
} |
|
1838 |
||
1839 |
// Iterate through monitor cache and attempt to release thread's monitors |
|
1840 |
// Gives up on a particular monitor if an exception occurs, but continues |
|
1841 |
// the overall iteration, swallowing the exception. |
|
1842 |
class ReleaseJavaMonitorsClosure: public MonitorClosure { |
|
1843 |
private: |
|
1844 |
TRAPS; |
|
1845 |
||
1846 |
public: |
|
1847 |
ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {} |
|
1848 |
void do_monitor(ObjectMonitor* mid) { |
|
1849 |
if (mid->owner() == THREAD) { |
|
1850 |
(void)mid->complete_exit(CHECK); |
|
1851 |
} |
|
1852 |
} |
|
1853 |
}; |
|
1854 |
||
1855 |
// Release all inflated monitors owned by THREAD. Lightweight monitors are |
|
1856 |
// ignored. This is meant to be called during JNI thread detach which assumes |
|
1857 |
// all remaining monitors are heavyweight. All exceptions are swallowed. |
|
1858 |
// Scanning the extant monitor list can be time consuming. |
|
1859 |
// A simple optimization is to add a per-thread flag that indicates a thread |
|
1860 |
// called jni_monitorenter() during its lifetime. |
|
1861 |
// |
|
1862 |
// Instead of No_Savepoint_Verifier it might be cheaper to |
|
1863 |
// use an idiom of the form: |
|
1864 |
// auto int tmp = SafepointSynchronize::_safepoint_counter ; |
|
1865 |
// <code that must not run at safepoint> |
|
1866 |
// guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; |
|
1867 |
// Since the tests are extremely cheap we could leave them enabled |
|
1868 |
// for normal product builds. |
|
1869 |
||
1870 |
void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) { |
|
1871 |
assert(THREAD == JavaThread::current(), "must be current Java thread"); |
|
1872 |
No_Safepoint_Verifier nsv ; |
|
1873 |
ReleaseJavaMonitorsClosure rjmc(THREAD); |
|
1874 |
Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread"); |
|
1875 |
ObjectSynchronizer::monitors_iterate(&rjmc); |
|
1876 |
Thread::muxRelease(&ListLock); |
|
1877 |
THREAD->clear_pending_exception(); |
|
1878 |
} |
|
1879 |
||
1880 |
// Visitors ... |
|
1881 |
||
1882 |
void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) { |
|
1883 |
ObjectMonitor* block = gBlockList; |
|
1884 |
ObjectMonitor* mid; |
|
1885 |
while (block) { |
|
1886 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
1887 |
for (int i = _BLOCKSIZE - 1; i > 0; i--) { |
|
1888 |
mid = block + i; |
|
1889 |
oop object = (oop) mid->object(); |
|
1890 |
if (object != NULL) { |
|
1891 |
closure->do_monitor(mid); |
|
1892 |
} |
|
1893 |
} |
|
1894 |
block = (ObjectMonitor*) block->FreeNext; |
|
1895 |
} |
|
1896 |
} |
|
1897 |
||
1898 |
void ObjectSynchronizer::oops_do(OopClosure* f) { |
|
1899 |
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
|
1900 |
for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
|
1901 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
1902 |
for (int i = 1; i < _BLOCKSIZE; i++) { |
|
1903 |
ObjectMonitor* mid = &block[i]; |
|
1904 |
if (mid->object() != NULL) { |
|
1905 |
f->do_oop((oop*)mid->object_addr()); |
|
1906 |
} |
|
1907 |
} |
|
1908 |
} |
|
1909 |
} |
|
1910 |
||
1911 |
// Deflate_idle_monitors() is called at all safepoints, immediately |
|
1912 |
// after all mutators are stopped, but before any objects have moved. |
|
1913 |
// It traverses the list of known monitors, deflating where possible. |
|
1914 |
// The scavenged monitor are returned to the monitor free list. |
|
1915 |
// |
|
1916 |
// Beware that we scavenge at *every* stop-the-world point. |
|
1917 |
// Having a large number of monitors in-circulation negatively |
|
1918 |
// impacts the performance of some applications (e.g., PointBase). |
|
1919 |
// Broadly, we want to minimize the # of monitors in circulation. |
|
5710 | 1920 |
// |
1921 |
// We have added a flag, MonitorInUseLists, which creates a list |
|
1922 |
// of active monitors for each thread. deflate_idle_monitors() |
|
1923 |
// only scans the per-thread inuse lists. omAlloc() puts all |
|
1924 |
// assigned monitors on the per-thread list. deflate_idle_monitors() |
|
1925 |
// returns the non-busy monitors to the global free list. |
|
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1926 |
// When a thread dies, omFlush() adds the list of active monitors for |
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|
1927 |
// that thread to a global gOmInUseList acquiring the |
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|
1928 |
// global list lock. deflate_idle_monitors() acquires the global |
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|
1929 |
// list lock to scan for non-busy monitors to the global free list. |
5710 | 1930 |
// An alternative could have used a single global inuse list. The |
1931 |
// downside would have been the additional cost of acquiring the global list lock |
|
1932 |
// for every omAlloc(). |
|
1 | 1933 |
// |
1934 |
// Perversely, the heap size -- and thus the STW safepoint rate -- |
|
1935 |
// typically drives the scavenge rate. Large heaps can mean infrequent GC, |
|
1936 |
// which in turn can mean large(r) numbers of objectmonitors in circulation. |
|
1937 |
// This is an unfortunate aspect of this design. |
|
1938 |
// |
|
1939 |
// Another refinement would be to refrain from calling deflate_idle_monitors() |
|
1940 |
// except at stop-the-world points associated with garbage collections. |
|
1941 |
// |
|
1942 |
// An even better solution would be to deflate on-the-fly, aggressively, |
|
1943 |
// at monitorexit-time as is done in EVM's metalock or Relaxed Locks. |
|
1944 |
||
5710 | 1945 |
|
1946 |
// Deflate a single monitor if not in use |
|
1947 |
// Return true if deflated, false if in use |
|
1948 |
bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj, |
|
1949 |
ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
|
1950 |
bool deflated; |
|
1951 |
// Normal case ... The monitor is associated with obj. |
|
1952 |
guarantee (obj->mark() == markOopDesc::encode(mid), "invariant") ; |
|
1953 |
guarantee (mid == obj->mark()->monitor(), "invariant"); |
|
1954 |
guarantee (mid->header()->is_neutral(), "invariant"); |
|
1955 |
||
1956 |
if (mid->is_busy()) { |
|
1957 |
if (ClearResponsibleAtSTW) mid->_Responsible = NULL ; |
|
1958 |
deflated = false; |
|
1959 |
} else { |
|
1960 |
// Deflate the monitor if it is no longer being used |
|
1961 |
// It's idle - scavenge and return to the global free list |
|
1962 |
// plain old deflation ... |
|
1963 |
TEVENT (deflate_idle_monitors - scavenge1) ; |
|
1964 |
if (TraceMonitorInflation) { |
|
1965 |
if (obj->is_instance()) { |
|
1966 |
ResourceMark rm; |
|
1967 |
tty->print_cr("Deflating object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", |
|
1968 |
(intptr_t) obj, (intptr_t) obj->mark(), Klass::cast(obj->klass())->external_name()); |
|
1969 |
} |
|
1970 |
} |
|
1971 |
||
1972 |
// Restore the header back to obj |
|
1973 |
obj->release_set_mark(mid->header()); |
|
1974 |
mid->clear(); |
|
1975 |
||
1976 |
assert (mid->object() == NULL, "invariant") ; |
|
1977 |
||
1978 |
// Move the object to the working free list defined by FreeHead,FreeTail. |
|
1979 |
if (*FreeHeadp == NULL) *FreeHeadp = mid; |
|
1980 |
if (*FreeTailp != NULL) { |
|
1981 |
ObjectMonitor * prevtail = *FreeTailp; |
|
5920
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|
1982 |
assert(prevtail->FreeNext == NULL, "cleaned up deflated?"); // TODO KK |
5710 | 1983 |
prevtail->FreeNext = mid; |
1984 |
} |
|
1985 |
*FreeTailp = mid; |
|
1986 |
deflated = true; |
|
1987 |
} |
|
1988 |
return deflated; |
|
1989 |
} |
|
1990 |
||
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|
1991 |
// Caller acquires ListLock |
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|
1992 |
int ObjectSynchronizer::walk_monitor_list(ObjectMonitor** listheadp, |
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|
1993 |
ObjectMonitor** FreeHeadp, ObjectMonitor** FreeTailp) { |
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|
1994 |
ObjectMonitor* mid; |
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|
1995 |
ObjectMonitor* next; |
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|
1996 |
ObjectMonitor* curmidinuse = NULL; |
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|
1997 |
int deflatedcount = 0; |
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|
1998 |
|
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|
1999 |
for (mid = *listheadp; mid != NULL; ) { |
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|
2000 |
oop obj = (oop) mid->object(); |
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|
2001 |
bool deflated = false; |
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|
2002 |
if (obj != NULL) { |
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|
2003 |
deflated = deflate_monitor(mid, obj, FreeHeadp, FreeTailp); |
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|
2004 |
} |
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|
2005 |
if (deflated) { |
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|
2006 |
// extract from per-thread in-use-list |
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|
2007 |
if (mid == *listheadp) { |
8fdbb85e62d3
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|
2008 |
*listheadp = mid->FreeNext; |
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|
2009 |
} else if (curmidinuse != NULL) { |
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|
2010 |
curmidinuse->FreeNext = mid->FreeNext; // maintain the current thread inuselist |
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|
2011 |
} |
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|
2012 |
next = mid->FreeNext; |
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|
2013 |
mid->FreeNext = NULL; // This mid is current tail in the FreeHead list |
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|
2014 |
mid = next; |
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|
2015 |
deflatedcount++; |
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|
2016 |
} else { |
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|
2017 |
curmidinuse = mid; |
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|
2018 |
mid = mid->FreeNext; |
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|
2019 |
} |
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|
2020 |
} |
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|
2021 |
return deflatedcount; |
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|
2022 |
} |
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|
2023 |
|
1 | 2024 |
void ObjectSynchronizer::deflate_idle_monitors() { |
2025 |
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint"); |
|
2026 |
int nInuse = 0 ; // currently associated with objects |
|
2027 |
int nInCirculation = 0 ; // extant |
|
2028 |
int nScavenged = 0 ; // reclaimed |
|
5710 | 2029 |
bool deflated = false; |
1 | 2030 |
|
2031 |
ObjectMonitor * FreeHead = NULL ; // Local SLL of scavenged monitors |
|
2032 |
ObjectMonitor * FreeTail = NULL ; |
|
2033 |
||
5710 | 2034 |
TEVENT (deflate_idle_monitors) ; |
2035 |
// Prevent omFlush from changing mids in Thread dtor's during deflation |
|
2036 |
// And in case the vm thread is acquiring a lock during a safepoint |
|
2037 |
// See e.g. 6320749 |
|
2038 |
Thread::muxAcquire (&ListLock, "scavenge - return") ; |
|
2039 |
||
2040 |
if (MonitorInUseLists) { |
|
5920
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|
2041 |
int inUse = 0; |
5710 | 2042 |
for (JavaThread* cur = Threads::first(); cur != NULL; cur = cur->next()) { |
5920
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|
2043 |
nInCirculation+= cur->omInUseCount; |
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|
2044 |
int deflatedcount = walk_monitor_list(cur->omInUseList_addr(), &FreeHead, &FreeTail); |
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|
2045 |
cur->omInUseCount-= deflatedcount; |
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|
2046 |
// verifyInUse(cur); |
8fdbb85e62d3
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|
2047 |
nScavenged += deflatedcount; |
8fdbb85e62d3
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|
2048 |
nInuse += cur->omInUseCount; |
5710 | 2049 |
} |
5920
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|
2050 |
|
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|
2051 |
// For moribund threads, scan gOmInUseList |
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|
2052 |
if (gOmInUseList) { |
8fdbb85e62d3
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|
2053 |
nInCirculation += gOmInUseCount; |
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|
2054 |
int deflatedcount = walk_monitor_list((ObjectMonitor **)&gOmInUseList, &FreeHead, &FreeTail); |
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|
2055 |
gOmInUseCount-= deflatedcount; |
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6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
2056 |
nScavenged += deflatedcount; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
2057 |
nInuse += gOmInUseCount; |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
2058 |
} |
8fdbb85e62d3
6964164: MonitorInUseLists leak of contended objects
acorn
parents:
5712
diff
changeset
|
2059 |
|
5710 | 2060 |
} else for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) { |
1 | 2061 |
// Iterate over all extant monitors - Scavenge all idle monitors. |
2062 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
2063 |
nInCirculation += _BLOCKSIZE ; |
|
2064 |
for (int i = 1 ; i < _BLOCKSIZE; i++) { |
|
2065 |
ObjectMonitor* mid = &block[i]; |
|
2066 |
oop obj = (oop) mid->object(); |
|
2067 |
||
2068 |
if (obj == NULL) { |
|
2069 |
// The monitor is not associated with an object. |
|
2070 |
// The monitor should either be a thread-specific private |
|
2071 |
// free list or the global free list. |
|
2072 |
// obj == NULL IMPLIES mid->is_busy() == 0 |
|
2073 |
guarantee (!mid->is_busy(), "invariant") ; |
|
2074 |
continue ; |
|
2075 |
} |
|
5710 | 2076 |
deflated = deflate_monitor(mid, obj, &FreeHead, &FreeTail); |
2077 |
||
2078 |
if (deflated) { |
|
2079 |
mid->FreeNext = NULL ; |
|
2080 |
nScavenged ++ ; |
|
1 | 2081 |
} else { |
5710 | 2082 |
nInuse ++; |
1 | 2083 |
} |
2084 |
} |
|
2085 |
} |
|
2086 |
||
5710 | 2087 |
MonitorFreeCount += nScavenged; |
2088 |
||
2089 |
// Consider: audit gFreeList to ensure that MonitorFreeCount and list agree. |
|
2090 |
||
2091 |
if (Knob_Verbose) { |
|
2092 |
::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n", |
|
2093 |
nInCirculation, nInuse, nScavenged, ForceMonitorScavenge, |
|
2094 |
MonitorPopulation, MonitorFreeCount) ; |
|
2095 |
::fflush(stdout) ; |
|
2096 |
} |
|
2097 |
||
2098 |
ForceMonitorScavenge = 0; // Reset |
|
2099 |
||
1 | 2100 |
// Move the scavenged monitors back to the global free list. |
2101 |
if (FreeHead != NULL) { |
|
2102 |
guarantee (FreeTail != NULL && nScavenged > 0, "invariant") ; |
|
2103 |
assert (FreeTail->FreeNext == NULL, "invariant") ; |
|
2104 |
// constant-time list splice - prepend scavenged segment to gFreeList |
|
2105 |
FreeTail->FreeNext = gFreeList ; |
|
2106 |
gFreeList = FreeHead ; |
|
2107 |
} |
|
5710 | 2108 |
Thread::muxRelease (&ListLock) ; |
1 | 2109 |
|
2110 |
if (_sync_Deflations != NULL) _sync_Deflations->inc(nScavenged) ; |
|
2111 |
if (_sync_MonExtant != NULL) _sync_MonExtant ->set_value(nInCirculation); |
|
2112 |
||
2113 |
// TODO: Add objectMonitor leak detection. |
|
2114 |
// Audit/inventory the objectMonitors -- make sure they're all accounted for. |
|
2115 |
GVars.stwRandom = os::random() ; |
|
2116 |
GVars.stwCycle ++ ; |
|
2117 |
} |
|
2118 |
||
2119 |
// A macro is used below because there may already be a pending |
|
2120 |
// exception which should not abort the execution of the routines |
|
2121 |
// which use this (which is why we don't put this into check_slow and |
|
2122 |
// call it with a CHECK argument). |
|
2123 |
||
2124 |
#define CHECK_OWNER() \ |
|
2125 |
do { \ |
|
2126 |
if (THREAD != _owner) { \ |
|
2127 |
if (THREAD->is_lock_owned((address) _owner)) { \ |
|
2128 |
_owner = THREAD ; /* Convert from basiclock addr to Thread addr */ \ |
|
2129 |
_recursions = 0; \ |
|
2130 |
OwnerIsThread = 1 ; \ |
|
2131 |
} else { \ |
|
2132 |
TEVENT (Throw IMSX) ; \ |
|
2133 |
THROW(vmSymbols::java_lang_IllegalMonitorStateException()); \ |
|
2134 |
} \ |
|
2135 |
} \ |
|
2136 |
} while (false) |
|
2137 |
||
2138 |
// TODO-FIXME: eliminate ObjectWaiters. Replace this visitor/enumerator |
|
2139 |
// interface with a simple FirstWaitingThread(), NextWaitingThread() interface. |
|
2140 |
||
2141 |
ObjectWaiter* ObjectMonitor::first_waiter() { |
|
2142 |
return _WaitSet; |
|
2143 |
} |
|
2144 |
||
2145 |
ObjectWaiter* ObjectMonitor::next_waiter(ObjectWaiter* o) { |
|
2146 |
return o->_next; |
|
2147 |
} |
|
2148 |
||
2149 |
Thread* ObjectMonitor::thread_of_waiter(ObjectWaiter* o) { |
|
2150 |
return o->_thread; |
|
2151 |
} |
|
2152 |
||
2153 |
// initialize the monitor, exception the semaphore, all other fields |
|
2154 |
// are simple integers or pointers |
|
2155 |
ObjectMonitor::ObjectMonitor() { |
|
2156 |
_header = NULL; |
|
2157 |
_count = 0; |
|
2158 |
_waiters = 0, |
|
2159 |
_recursions = 0; |
|
2160 |
_object = NULL; |
|
2161 |
_owner = NULL; |
|
2162 |
_WaitSet = NULL; |
|
2163 |
_WaitSetLock = 0 ; |
|
2164 |
_Responsible = NULL ; |
|
2165 |
_succ = NULL ; |
|
2166 |
_cxq = NULL ; |
|
2167 |
FreeNext = NULL ; |
|
2168 |
_EntryList = NULL ; |
|
2169 |
_SpinFreq = 0 ; |
|
2170 |
_SpinClock = 0 ; |
|
2171 |
OwnerIsThread = 0 ; |
|
2172 |
} |
|
2173 |
||
2174 |
ObjectMonitor::~ObjectMonitor() { |
|
2175 |
// TODO: Add asserts ... |
|
2176 |
// _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 |
|
2177 |
// _count == 0 _EntryList == NULL etc |
|
2178 |
} |
|
2179 |
||
2180 |
intptr_t ObjectMonitor::is_busy() const { |
|
2181 |
// TODO-FIXME: merge _count and _waiters. |
|
2182 |
// TODO-FIXME: assert _owner == null implies _recursions = 0 |
|
2183 |
// TODO-FIXME: assert _WaitSet != null implies _count > 0 |
|
2184 |
return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList ) ; |
|
2185 |
} |
|
2186 |
||
2187 |
void ObjectMonitor::Recycle () { |
|
2188 |
// TODO: add stronger asserts ... |
|
2189 |
// _cxq == 0 _succ == NULL _owner == NULL _waiters == 0 |
|
2190 |
// _count == 0 EntryList == NULL |
|
2191 |
// _recursions == 0 _WaitSet == NULL |
|
2192 |
// TODO: assert (is_busy()|_recursions) == 0 |
|
2193 |
_succ = NULL ; |
|
2194 |
_EntryList = NULL ; |
|
2195 |
_cxq = NULL ; |
|
2196 |
_WaitSet = NULL ; |
|
2197 |
_recursions = 0 ; |
|
2198 |
_SpinFreq = 0 ; |
|
2199 |
_SpinClock = 0 ; |
|
2200 |
OwnerIsThread = 0 ; |
|
2201 |
} |
|
2202 |
||
2203 |
// WaitSet management ... |
|
2204 |
||
2205 |
inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) { |
|
2206 |
assert(node != NULL, "should not dequeue NULL node"); |
|
2207 |
assert(node->_prev == NULL, "node already in list"); |
|
2208 |
assert(node->_next == NULL, "node already in list"); |
|
2209 |
// put node at end of queue (circular doubly linked list) |
|
2210 |
if (_WaitSet == NULL) { |
|
2211 |
_WaitSet = node; |
|
2212 |
node->_prev = node; |
|
2213 |
node->_next = node; |
|
2214 |
} else { |
|
2215 |
ObjectWaiter* head = _WaitSet ; |
|
2216 |
ObjectWaiter* tail = head->_prev; |
|
2217 |
assert(tail->_next == head, "invariant check"); |
|
2218 |
tail->_next = node; |
|
2219 |
head->_prev = node; |
|
2220 |
node->_next = head; |
|
2221 |
node->_prev = tail; |
|
2222 |
} |
|
2223 |
} |
|
2224 |
||
2225 |
inline ObjectWaiter* ObjectMonitor::DequeueWaiter() { |
|
2226 |
// dequeue the very first waiter |
|
2227 |
ObjectWaiter* waiter = _WaitSet; |
|
2228 |
if (waiter) { |
|
2229 |
DequeueSpecificWaiter(waiter); |
|
2230 |
} |
|
2231 |
return waiter; |
|
2232 |
} |
|
2233 |
||
2234 |
inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) { |
|
2235 |
assert(node != NULL, "should not dequeue NULL node"); |
|
2236 |
assert(node->_prev != NULL, "node already removed from list"); |
|
2237 |
assert(node->_next != NULL, "node already removed from list"); |
|
2238 |
// when the waiter has woken up because of interrupt, |
|
2239 |
// timeout or other spurious wake-up, dequeue the |
|
2240 |
// waiter from waiting list |
|
2241 |
ObjectWaiter* next = node->_next; |
|
2242 |
if (next == node) { |
|
2243 |
assert(node->_prev == node, "invariant check"); |
|
2244 |
_WaitSet = NULL; |
|
2245 |
} else { |
|
2246 |
ObjectWaiter* prev = node->_prev; |
|
2247 |
assert(prev->_next == node, "invariant check"); |
|
2248 |
assert(next->_prev == node, "invariant check"); |
|
2249 |
next->_prev = prev; |
|
2250 |
prev->_next = next; |
|
2251 |
if (_WaitSet == node) { |
|
2252 |
_WaitSet = next; |
|
2253 |
} |
|
2254 |
} |
|
2255 |
node->_next = NULL; |
|
2256 |
node->_prev = NULL; |
|
2257 |
} |
|
2258 |
||
2259 |
static char * kvGet (char * kvList, const char * Key) { |
|
2260 |
if (kvList == NULL) return NULL ; |
|
2261 |
size_t n = strlen (Key) ; |
|
2262 |
char * Search ; |
|
2263 |
for (Search = kvList ; *Search ; Search += strlen(Search) + 1) { |
|
2264 |
if (strncmp (Search, Key, n) == 0) { |
|
2265 |
if (Search[n] == '=') return Search + n + 1 ; |
|
2266 |
if (Search[n] == 0) return (char *) "1" ; |
|
2267 |
} |
|
2268 |
} |
|
2269 |
return NULL ; |
|
2270 |
} |
|
2271 |
||
2272 |
static int kvGetInt (char * kvList, const char * Key, int Default) { |
|
2273 |
char * v = kvGet (kvList, Key) ; |
|
2274 |
int rslt = v ? ::strtol (v, NULL, 0) : Default ; |
|
2275 |
if (Knob_ReportSettings && v != NULL) { |
|
2276 |
::printf (" SyncKnob: %s %d(%d)\n", Key, rslt, Default) ; |
|
2277 |
::fflush (stdout) ; |
|
2278 |
} |
|
2279 |
return rslt ; |
|
2280 |
} |
|
2281 |
||
2282 |
// By convention we unlink a contending thread from EntryList|cxq immediately |
|
2283 |
// after the thread acquires the lock in ::enter(). Equally, we could defer |
|
2284 |
// unlinking the thread until ::exit()-time. |
|
2285 |
||
2286 |
void ObjectMonitor::UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode) |
|
2287 |
{ |
|
2288 |
assert (_owner == Self, "invariant") ; |
|
2289 |
assert (SelfNode->_thread == Self, "invariant") ; |
|
2290 |
||
2291 |
if (SelfNode->TState == ObjectWaiter::TS_ENTER) { |
|
2292 |
// Normal case: remove Self from the DLL EntryList . |
|
2293 |
// This is a constant-time operation. |
|
2294 |
ObjectWaiter * nxt = SelfNode->_next ; |
|
2295 |
ObjectWaiter * prv = SelfNode->_prev ; |
|
2296 |
if (nxt != NULL) nxt->_prev = prv ; |
|
2297 |
if (prv != NULL) prv->_next = nxt ; |
|
2298 |
if (SelfNode == _EntryList ) _EntryList = nxt ; |
|
2299 |
assert (nxt == NULL || nxt->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
2300 |
assert (prv == NULL || prv->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
2301 |
TEVENT (Unlink from EntryList) ; |
|
2302 |
} else { |
|
2303 |
guarantee (SelfNode->TState == ObjectWaiter::TS_CXQ, "invariant") ; |
|
2304 |
// Inopportune interleaving -- Self is still on the cxq. |
|
2305 |
// This usually means the enqueue of self raced an exiting thread. |
|
2306 |
// Normally we'll find Self near the front of the cxq, so |
|
2307 |
// dequeueing is typically fast. If needbe we can accelerate |
|
2308 |
// this with some MCS/CHL-like bidirectional list hints and advisory |
|
2309 |
// back-links so dequeueing from the interior will normally operate |
|
2310 |
// in constant-time. |
|
2311 |
// Dequeue Self from either the head (with CAS) or from the interior |
|
2312 |
// with a linear-time scan and normal non-atomic memory operations. |
|
2313 |
// CONSIDER: if Self is on the cxq then simply drain cxq into EntryList |
|
2314 |
// and then unlink Self from EntryList. We have to drain eventually, |
|
2315 |
// so it might as well be now. |
|
2316 |
||
2317 |
ObjectWaiter * v = _cxq ; |
|
2318 |
assert (v != NULL, "invariant") ; |
|
2319 |
if (v != SelfNode || Atomic::cmpxchg_ptr (SelfNode->_next, &_cxq, v) != v) { |
|
2320 |
// The CAS above can fail from interference IFF a "RAT" arrived. |
|
2321 |
// In that case Self must be in the interior and can no longer be |
|
2322 |
// at the head of cxq. |
|
2323 |
if (v == SelfNode) { |
|
2324 |
assert (_cxq != v, "invariant") ; |
|
2325 |
v = _cxq ; // CAS above failed - start scan at head of list |
|
2326 |
} |
|
2327 |
ObjectWaiter * p ; |
|
2328 |
ObjectWaiter * q = NULL ; |
|
2329 |
for (p = v ; p != NULL && p != SelfNode; p = p->_next) { |
|
2330 |
q = p ; |
|
2331 |
assert (p->TState == ObjectWaiter::TS_CXQ, "invariant") ; |
|
2332 |
} |
|
2333 |
assert (v != SelfNode, "invariant") ; |
|
2334 |
assert (p == SelfNode, "Node not found on cxq") ; |
|
2335 |
assert (p != _cxq, "invariant") ; |
|
2336 |
assert (q != NULL, "invariant") ; |
|
2337 |
assert (q->_next == p, "invariant") ; |
|
2338 |
q->_next = p->_next ; |
|
2339 |
} |
|
2340 |
TEVENT (Unlink from cxq) ; |
|
2341 |
} |
|
2342 |
||
2343 |
// Diagnostic hygiene ... |
|
2344 |
SelfNode->_prev = (ObjectWaiter *) 0xBAD ; |
|
2345 |
SelfNode->_next = (ObjectWaiter *) 0xBAD ; |
|
2346 |
SelfNode->TState = ObjectWaiter::TS_RUN ; |
|
2347 |
} |
|
2348 |
||
2349 |
// Caveat: TryLock() is not necessarily serializing if it returns failure. |
|
2350 |
// Callers must compensate as needed. |
|
2351 |
||
2352 |
int ObjectMonitor::TryLock (Thread * Self) { |
|
2353 |
for (;;) { |
|
2354 |
void * own = _owner ; |
|
2355 |
if (own != NULL) return 0 ; |
|
2356 |
if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) { |
|
2357 |
// Either guarantee _recursions == 0 or set _recursions = 0. |
|
2358 |
assert (_recursions == 0, "invariant") ; |
|
2359 |
assert (_owner == Self, "invariant") ; |
|
2360 |
// CONSIDER: set or assert that OwnerIsThread == 1 |
|
2361 |
return 1 ; |
|
2362 |
} |
|
2363 |
// The lock had been free momentarily, but we lost the race to the lock. |
|
2364 |
// Interference -- the CAS failed. |
|
2365 |
// We can either return -1 or retry. |
|
2366 |
// Retry doesn't make as much sense because the lock was just acquired. |
|
2367 |
if (true) return -1 ; |
|
2368 |
} |
|
2369 |
} |
|
2370 |
||
2371 |
// NotRunnable() -- informed spinning |
|
2372 |
// |
|
2373 |
// Don't bother spinning if the owner is not eligible to drop the lock. |
|
2374 |
// Peek at the owner's schedctl.sc_state and Thread._thread_values and |
|
2375 |
// spin only if the owner thread is _thread_in_Java or _thread_in_vm. |
|
2376 |
// The thread must be runnable in order to drop the lock in timely fashion. |
|
2377 |
// If the _owner is not runnable then spinning will not likely be |
|
2378 |
// successful (profitable). |
|
2379 |
// |
|
2380 |
// Beware -- the thread referenced by _owner could have died |
|
2381 |
// so a simply fetch from _owner->_thread_state might trap. |
|
2382 |
// Instead, we use SafeFetchXX() to safely LD _owner->_thread_state. |
|
2383 |
// Because of the lifecycle issues the schedctl and _thread_state values |
|
2384 |
// observed by NotRunnable() might be garbage. NotRunnable must |
|
2385 |
// tolerate this and consider the observed _thread_state value |
|
2386 |
// as advisory. |
|
2387 |
// |
|
2388 |
// Beware too, that _owner is sometimes a BasicLock address and sometimes |
|
2389 |
// a thread pointer. We differentiate the two cases with OwnerIsThread. |
|
2390 |
// Alternately, we might tag the type (thread pointer vs basiclock pointer) |
|
2391 |
// with the LSB of _owner. Another option would be to probablistically probe |
|
2392 |
// the putative _owner->TypeTag value. |
|
2393 |
// |
|
2394 |
// Checking _thread_state isn't perfect. Even if the thread is |
|
2395 |
// in_java it might be blocked on a page-fault or have been preempted |
|
2396 |
// and sitting on a ready/dispatch queue. _thread state in conjunction |
|
2397 |
// with schedctl.sc_state gives us a good picture of what the |
|
2398 |
// thread is doing, however. |
|
2399 |
// |
|
2400 |
// TODO: check schedctl.sc_state. |
|
2401 |
// We'll need to use SafeFetch32() to read from the schedctl block. |
|
2402 |
// See RFE #5004247 and http://sac.sfbay.sun.com/Archives/CaseLog/arc/PSARC/2005/351/ |
|
2403 |
// |
|
2404 |
// The return value from NotRunnable() is *advisory* -- the |
|
2405 |
// result is based on sampling and is not necessarily coherent. |
|
2406 |
// The caller must tolerate false-negative and false-positive errors. |
|
2407 |
// Spinning, in general, is probabilistic anyway. |
|
2408 |
||
2409 |
||
2410 |
int ObjectMonitor::NotRunnable (Thread * Self, Thread * ox) { |
|
2411 |
// Check either OwnerIsThread or ox->TypeTag == 2BAD. |
|
2412 |
if (!OwnerIsThread) return 0 ; |
|
2413 |
||
2414 |
if (ox == NULL) return 0 ; |
|
2415 |
||
2416 |
// Avoid transitive spinning ... |
|
2417 |
// Say T1 spins or blocks trying to acquire L. T1._Stalled is set to L. |
|
2418 |
// Immediately after T1 acquires L it's possible that T2, also |
|
2419 |
// spinning on L, will see L.Owner=T1 and T1._Stalled=L. |
|
2420 |
// This occurs transiently after T1 acquired L but before |
|
2421 |
// T1 managed to clear T1.Stalled. T2 does not need to abort |
|
2422 |
// its spin in this circumstance. |
|
2423 |
intptr_t BlockedOn = SafeFetchN ((intptr_t *) &ox->_Stalled, intptr_t(1)) ; |
|
2424 |
||
2425 |
if (BlockedOn == 1) return 1 ; |
|
2426 |
if (BlockedOn != 0) { |
|
2427 |
return BlockedOn != intptr_t(this) && _owner == ox ; |
|
2428 |
} |
|
2429 |
||
2430 |
assert (sizeof(((JavaThread *)ox)->_thread_state == sizeof(int)), "invariant") ; |
|
2431 |
int jst = SafeFetch32 ((int *) &((JavaThread *) ox)->_thread_state, -1) ; ; |
|
2432 |
// consider also: jst != _thread_in_Java -- but that's overspecific. |
|
2433 |
return jst == _thread_blocked || jst == _thread_in_native ; |
|
2434 |
} |
|
2435 |
||
2436 |
||
2437 |
// Adaptive spin-then-block - rational spinning |
|
2438 |
// |
|
2439 |
// Note that we spin "globally" on _owner with a classic SMP-polite TATAS |
|
2440 |
// algorithm. On high order SMP systems it would be better to start with |
|
2441 |
// a brief global spin and then revert to spinning locally. In the spirit of MCS/CLH, |
|
2442 |
// a contending thread could enqueue itself on the cxq and then spin locally |
|
2443 |
// on a thread-specific variable such as its ParkEvent._Event flag. |
|
2444 |
// That's left as an exercise for the reader. Note that global spinning is |
|
2445 |
// not problematic on Niagara, as the L2$ serves the interconnect and has both |
|
2446 |
// low latency and massive bandwidth. |
|
2447 |
// |
|
2448 |
// Broadly, we can fix the spin frequency -- that is, the % of contended lock |
|
2449 |
// acquisition attempts where we opt to spin -- at 100% and vary the spin count |
|
2450 |
// (duration) or we can fix the count at approximately the duration of |
|
2451 |
// a context switch and vary the frequency. Of course we could also |
|
2452 |
// vary both satisfying K == Frequency * Duration, where K is adaptive by monitor. |
|
2453 |
// See http://j2se.east/~dice/PERSIST/040824-AdaptiveSpinning.html. |
|
2454 |
// |
|
2455 |
// This implementation varies the duration "D", where D varies with |
|
2456 |
// the success rate of recent spin attempts. (D is capped at approximately |
|
2457 |
// length of a round-trip context switch). The success rate for recent |
|
2458 |
// spin attempts is a good predictor of the success rate of future spin |
|
2459 |
// attempts. The mechanism adapts automatically to varying critical |
|
2460 |
// section length (lock modality), system load and degree of parallelism. |
|
2461 |
// D is maintained per-monitor in _SpinDuration and is initialized |
|
2462 |
// optimistically. Spin frequency is fixed at 100%. |
|
2463 |
// |
|
2464 |
// Note that _SpinDuration is volatile, but we update it without locks |
|
2465 |
// or atomics. The code is designed so that _SpinDuration stays within |
|
2466 |
// a reasonable range even in the presence of races. The arithmetic |
|
2467 |
// operations on _SpinDuration are closed over the domain of legal values, |
|
2468 |
// so at worst a race will install and older but still legal value. |
|
2469 |
// At the very worst this introduces some apparent non-determinism. |
|
2470 |
// We might spin when we shouldn't or vice-versa, but since the spin |
|
2471 |
// count are relatively short, even in the worst case, the effect is harmless. |
|
2472 |
// |
|
2473 |
// Care must be taken that a low "D" value does not become an |
|
2474 |
// an absorbing state. Transient spinning failures -- when spinning |
|
2475 |
// is overall profitable -- should not cause the system to converge |
|
2476 |
// on low "D" values. We want spinning to be stable and predictable |
|
2477 |
// and fairly responsive to change and at the same time we don't want |
|
2478 |
// it to oscillate, become metastable, be "too" non-deterministic, |
|
2479 |
// or converge on or enter undesirable stable absorbing states. |
|
2480 |
// |
|
2481 |
// We implement a feedback-based control system -- using past behavior |
|
2482 |
// to predict future behavior. We face two issues: (a) if the |
|
2483 |
// input signal is random then the spin predictor won't provide optimal |
|
2484 |
// results, and (b) if the signal frequency is too high then the control |
|
2485 |
// system, which has some natural response lag, will "chase" the signal. |
|
2486 |
// (b) can arise from multimodal lock hold times. Transient preemption |
|
2487 |
// can also result in apparent bimodal lock hold times. |
|
2488 |
// Although sub-optimal, neither condition is particularly harmful, as |
|
2489 |
// in the worst-case we'll spin when we shouldn't or vice-versa. |
|
2490 |
// The maximum spin duration is rather short so the failure modes aren't bad. |
|
2491 |
// To be conservative, I've tuned the gain in system to bias toward |
|
2492 |
// _not spinning. Relatedly, the system can sometimes enter a mode where it |
|
2493 |
// "rings" or oscillates between spinning and not spinning. This happens |
|
2494 |
// when spinning is just on the cusp of profitability, however, so the |
|
2495 |
// situation is not dire. The state is benign -- there's no need to add |
|
2496 |
// hysteresis control to damp the transition rate between spinning and |
|
2497 |
// not spinning. |
|
2498 |
// |
|
2499 |
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - |
|
2500 |
// |
|
2501 |
// Spin-then-block strategies ... |
|
2502 |
// |
|
2503 |
// Thoughts on ways to improve spinning : |
|
2504 |
// |
|
2505 |
// * Periodically call {psr_}getloadavg() while spinning, and |
|
2506 |
// permit unbounded spinning if the load average is < |
|
2507 |
// the number of processors. Beware, however, that getloadavg() |
|
2508 |
// is exceptionally fast on solaris (about 1/10 the cost of a full |
|
2509 |
// spin cycle, but quite expensive on linux. Beware also, that |
|
2510 |
// multiple JVMs could "ring" or oscillate in a feedback loop. |
|
2511 |
// Sufficient damping would solve that problem. |
|
2512 |
// |
|
2513 |
// * We currently use spin loops with iteration counters to approximate |
|
2514 |
// spinning for some interval. Given the availability of high-precision |
|
2515 |
// time sources such as gethrtime(), %TICK, %STICK, RDTSC, etc., we should |
|
2516 |
// someday reimplement the spin loops to duration-based instead of iteration-based. |
|
2517 |
// |
|
2518 |
// * Don't spin if there are more than N = (CPUs/2) threads |
|
2519 |
// currently spinning on the monitor (or globally). |
|
2520 |
// That is, limit the number of concurrent spinners. |
|
2521 |
// We might also limit the # of spinners in the JVM, globally. |
|
2522 |
// |
|
2523 |
// * If a spinning thread observes _owner change hands it should |
|
2524 |
// abort the spin (and park immediately) or at least debit |
|
2525 |
// the spin counter by a large "penalty". |
|
2526 |
// |
|
2527 |
// * Classically, the spin count is either K*(CPUs-1) or is a |
|
2528 |
// simple constant that approximates the length of a context switch. |
|
2529 |
// We currently use a value -- computed by a special utility -- that |
|
2530 |
// approximates round-trip context switch times. |
|
2531 |
// |
|
2532 |
// * Normally schedctl_start()/_stop() is used to advise the kernel |
|
2533 |
// to avoid preempting threads that are running in short, bounded |
|
2534 |
// critical sections. We could use the schedctl hooks in an inverted |
|
2535 |
// sense -- spinners would set the nopreempt flag, but poll the preempt |
|
2536 |
// pending flag. If a spinner observed a pending preemption it'd immediately |
|
2537 |
// abort the spin and park. As such, the schedctl service acts as |
|
2538 |
// a preemption warning mechanism. |
|
2539 |
// |
|
2540 |
// * In lieu of spinning, if the system is running below saturation |
|
2541 |
// (that is, loadavg() << #cpus), we can instead suppress futile |
|
2542 |
// wakeup throttling, or even wake more than one successor at exit-time. |
|
2543 |
// The net effect is largely equivalent to spinning. In both cases, |
|
2544 |
// contending threads go ONPROC and opportunistically attempt to acquire |
|
2545 |
// the lock, decreasing lock handover latency at the expense of wasted |
|
2546 |
// cycles and context switching. |
|
2547 |
// |
|
2548 |
// * We might to spin less after we've parked as the thread will |
|
2549 |
// have less $ and TLB affinity with the processor. |
|
2550 |
// Likewise, we might spin less if we come ONPROC on a different |
|
2551 |
// processor or after a long period (>> rechose_interval). |
|
2552 |
// |
|
2553 |
// * A table-driven state machine similar to Solaris' dispadmin scheduling |
|
2554 |
// tables might be a better design. Instead of encoding information in |
|
2555 |
// _SpinDuration, _SpinFreq and _SpinClock we'd just use explicit, |
|
2556 |
// discrete states. Success or failure during a spin would drive |
|
2557 |
// state transitions, and each state node would contain a spin count. |
|
2558 |
// |
|
2559 |
// * If the processor is operating in a mode intended to conserve power |
|
2560 |
// (such as Intel's SpeedStep) or to reduce thermal output (thermal |
|
2561 |
// step-down mode) then the Java synchronization subsystem should |
|
2562 |
// forgo spinning. |
|
2563 |
// |
|
2564 |
// * The minimum spin duration should be approximately the worst-case |
|
2565 |
// store propagation latency on the platform. That is, the time |
|
2566 |
// it takes a store on CPU A to become visible on CPU B, where A and |
|
2567 |
// B are "distant". |
|
2568 |
// |
|
2569 |
// * We might want to factor a thread's priority in the spin policy. |
|
2570 |
// Threads with a higher priority might spin for slightly longer. |
|
2571 |
// Similarly, if we use back-off in the TATAS loop, lower priority |
|
2572 |
// threads might back-off longer. We don't currently use a |
|
2573 |
// thread's priority when placing it on the entry queue. We may |
|
2574 |
// want to consider doing so in future releases. |
|
2575 |
// |
|
2576 |
// * We might transiently drop a thread's scheduling priority while it spins. |
|
2577 |
// SCHED_BATCH on linux and FX scheduling class at priority=0 on Solaris |
|
2578 |
// would suffice. We could even consider letting the thread spin indefinitely at |
|
2579 |
// a depressed or "idle" priority. This brings up fairness issues, however -- |
|
2580 |
// in a saturated system a thread would with a reduced priority could languish |
|
2581 |
// for extended periods on the ready queue. |
|
2582 |
// |
|
2583 |
// * While spinning try to use the otherwise wasted time to help the VM make |
|
2584 |
// progress: |
|
2585 |
// |
|
2586 |
// -- YieldTo() the owner, if the owner is OFFPROC but ready |
|
2587 |
// Done our remaining quantum directly to the ready thread. |
|
2588 |
// This helps "push" the lock owner through the critical section. |
|
2589 |
// It also tends to improve affinity/locality as the lock |
|
2590 |
// "migrates" less frequently between CPUs. |
|
2591 |
// -- Walk our own stack in anticipation of blocking. Memoize the roots. |
|
2592 |
// -- Perform strand checking for other thread. Unpark potential strandees. |
|
2593 |
// -- Help GC: trace or mark -- this would need to be a bounded unit of work. |
|
2594 |
// Unfortunately this will pollute our $ and TLBs. Recall that we |
|
2595 |
// spin to avoid context switching -- context switching has an |
|
2596 |
// immediate cost in latency, a disruptive cost to other strands on a CMT |
|
2597 |
// processor, and an amortized cost because of the D$ and TLB cache |
|
2598 |
// reload transient when the thread comes back ONPROC and repopulates |
|
2599 |
// $s and TLBs. |
|
2600 |
// -- call getloadavg() to see if the system is saturated. It'd probably |
|
2601 |
// make sense to call getloadavg() half way through the spin. |
|
2602 |
// If the system isn't at full capacity the we'd simply reset |
|
2603 |
// the spin counter to and extend the spin attempt. |
|
2604 |
// -- Doug points out that we should use the same "helping" policy |
|
2605 |
// in thread.yield(). |
|
2606 |
// |
|
2607 |
// * Try MONITOR-MWAIT on systems that support those instructions. |
|
2608 |
// |
|
2609 |
// * The spin statistics that drive spin decisions & frequency are |
|
2610 |
// maintained in the objectmonitor structure so if we deflate and reinflate |
|
2611 |
// we lose spin state. In practice this is not usually a concern |
|
2612 |
// as the default spin state after inflation is aggressive (optimistic) |
|
2613 |
// and tends toward spinning. So in the worst case for a lock where |
|
2614 |
// spinning is not profitable we may spin unnecessarily for a brief |
|
2615 |
// period. But then again, if a lock is contended it'll tend not to deflate |
|
2616 |
// in the first place. |
|
2617 |
||
2618 |
||
2619 |
intptr_t ObjectMonitor::SpinCallbackArgument = 0 ; |
|
2620 |
int (*ObjectMonitor::SpinCallbackFunction)(intptr_t, int) = NULL ; |
|
2621 |
||
2622 |
// Spinning: Fixed frequency (100%), vary duration |
|
2623 |
||
2624 |
int ObjectMonitor::TrySpin_VaryDuration (Thread * Self) { |
|
2625 |
||
2626 |
// Dumb, brutal spin. Good for comparative measurements against adaptive spinning. |
|
2627 |
int ctr = Knob_FixedSpin ; |
|
2628 |
if (ctr != 0) { |
|
2629 |
while (--ctr >= 0) { |
|
2630 |
if (TryLock (Self) > 0) return 1 ; |
|
2631 |
SpinPause () ; |
|
2632 |
} |
|
2633 |
return 0 ; |
|
2634 |
} |
|
2635 |
||
2636 |
for (ctr = Knob_PreSpin + 1; --ctr >= 0 ; ) { |
|
2637 |
if (TryLock(Self) > 0) { |
|
2638 |
// Increase _SpinDuration ... |
|
2639 |
// Note that we don't clamp SpinDuration precisely at SpinLimit. |
|
2640 |
// Raising _SpurDuration to the poverty line is key. |
|
2641 |
int x = _SpinDuration ; |
|
2642 |
if (x < Knob_SpinLimit) { |
|
2643 |
if (x < Knob_Poverty) x = Knob_Poverty ; |
|
2644 |
_SpinDuration = x + Knob_BonusB ; |
|
2645 |
} |
|
2646 |
return 1 ; |
|
2647 |
} |
|
2648 |
SpinPause () ; |
|
2649 |
} |
|
2650 |
||
2651 |
// Admission control - verify preconditions for spinning |
|
2652 |
// |
|
2653 |
// We always spin a little bit, just to prevent _SpinDuration == 0 from |
|
2654 |
// becoming an absorbing state. Put another way, we spin briefly to |
|
2655 |
// sample, just in case the system load, parallelism, contention, or lock |
|
2656 |
// modality changed. |
|
2657 |
// |
|
2658 |
// Consider the following alternative: |
|
2659 |
// Periodically set _SpinDuration = _SpinLimit and try a long/full |
|
2660 |
// spin attempt. "Periodically" might mean after a tally of |
|
2661 |
// the # of failed spin attempts (or iterations) reaches some threshold. |
|
2662 |
// This takes us into the realm of 1-out-of-N spinning, where we |
|
2663 |
// hold the duration constant but vary the frequency. |
|
2664 |
||
2665 |
ctr = _SpinDuration ; |
|
2666 |
if (ctr < Knob_SpinBase) ctr = Knob_SpinBase ; |
|
2667 |
if (ctr <= 0) return 0 ; |
|
2668 |
||
2669 |
if (Knob_SuccRestrict && _succ != NULL) return 0 ; |
|
2670 |
if (Knob_OState && NotRunnable (Self, (Thread *) _owner)) { |
|
2671 |
TEVENT (Spin abort - notrunnable [TOP]); |
|
2672 |
return 0 ; |
|
2673 |
} |
|
2674 |
||
2675 |
int MaxSpin = Knob_MaxSpinners ; |
|
2676 |
if (MaxSpin >= 0) { |
|
2677 |
if (_Spinner > MaxSpin) { |
|
2678 |
TEVENT (Spin abort -- too many spinners) ; |
|
2679 |
return 0 ; |
|
2680 |
} |
|
2681 |
// Slighty racy, but benign ... |
|
2682 |
Adjust (&_Spinner, 1) ; |
|
2683 |
} |
|
2684 |
||
2685 |
// We're good to spin ... spin ingress. |
|
2686 |
// CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades |
|
2687 |
// when preparing to LD...CAS _owner, etc and the CAS is likely |
|
2688 |
// to succeed. |
|
2689 |
int hits = 0 ; |
|
2690 |
int msk = 0 ; |
|
2691 |
int caspty = Knob_CASPenalty ; |
|
2692 |
int oxpty = Knob_OXPenalty ; |
|
2693 |
int sss = Knob_SpinSetSucc ; |
|
2694 |
if (sss && _succ == NULL ) _succ = Self ; |
|
2695 |
Thread * prv = NULL ; |
|
2696 |
||
2697 |
// There are three ways to exit the following loop: |
|
2698 |
// 1. A successful spin where this thread has acquired the lock. |
|
2699 |
// 2. Spin failure with prejudice |
|
2700 |
// 3. Spin failure without prejudice |
|
2701 |
||
2702 |
while (--ctr >= 0) { |
|
2703 |
||
2704 |
// Periodic polling -- Check for pending GC |
|
2705 |
// Threads may spin while they're unsafe. |
|
2706 |
// We don't want spinning threads to delay the JVM from reaching |
|
2707 |
// a stop-the-world safepoint or to steal cycles from GC. |
|
2708 |
// If we detect a pending safepoint we abort in order that |
|
2709 |
// (a) this thread, if unsafe, doesn't delay the safepoint, and (b) |
|
2710 |
// this thread, if safe, doesn't steal cycles from GC. |
|
2711 |
// This is in keeping with the "no loitering in runtime" rule. |
|
2712 |
// We periodically check to see if there's a safepoint pending. |
|
2713 |
if ((ctr & 0xFF) == 0) { |
|
2714 |
if (SafepointSynchronize::do_call_back()) { |
|
2715 |
TEVENT (Spin: safepoint) ; |
|
2716 |
goto Abort ; // abrupt spin egress |
|
2717 |
} |
|
2718 |
if (Knob_UsePause & 1) SpinPause () ; |
|
2719 |
||
2720 |
int (*scb)(intptr_t,int) = SpinCallbackFunction ; |
|
2721 |
if (hits > 50 && scb != NULL) { |
|
2722 |
int abend = (*scb)(SpinCallbackArgument, 0) ; |
|
2723 |
} |
|
2724 |
} |
|
2725 |
||
2726 |
if (Knob_UsePause & 2) SpinPause() ; |
|
2727 |
||
2728 |
// Exponential back-off ... Stay off the bus to reduce coherency traffic. |
|
2729 |
// This is useful on classic SMP systems, but is of less utility on |
|
2730 |
// N1-style CMT platforms. |
|
2731 |
// |
|
2732 |
// Trade-off: lock acquisition latency vs coherency bandwidth. |
|
2733 |
// Lock hold times are typically short. A histogram |
|
2734 |
// of successful spin attempts shows that we usually acquire |
|
2735 |
// the lock early in the spin. That suggests we want to |
|
2736 |
// sample _owner frequently in the early phase of the spin, |
|
2737 |
// but then back-off and sample less frequently as the spin |
|
2738 |
// progresses. The back-off makes a good citizen on SMP big |
|
2739 |
// SMP systems. Oversampling _owner can consume excessive |
|
2740 |
// coherency bandwidth. Relatedly, if we _oversample _owner we |
|
2741 |
// can inadvertently interfere with the the ST m->owner=null. |
|
2742 |
// executed by the lock owner. |
|
2743 |
if (ctr & msk) continue ; |
|
2744 |
++hits ; |
|
2745 |
if ((hits & 0xF) == 0) { |
|
2746 |
// The 0xF, above, corresponds to the exponent. |
|
2747 |
// Consider: (msk+1)|msk |
|
2748 |
msk = ((msk << 2)|3) & BackOffMask ; |
|
2749 |
} |
|
2750 |
||
2751 |
// Probe _owner with TATAS |
|
2752 |
// If this thread observes the monitor transition or flicker |
|
2753 |
// from locked to unlocked to locked, then the odds that this |
|
2754 |
// thread will acquire the lock in this spin attempt go down |
|
2755 |
// considerably. The same argument applies if the CAS fails |
|
2756 |
// or if we observe _owner change from one non-null value to |
|
2757 |
// another non-null value. In such cases we might abort |
|
2758 |
// the spin without prejudice or apply a "penalty" to the |
|
2759 |
// spin count-down variable "ctr", reducing it by 100, say. |
|
2760 |
||
2761 |
Thread * ox = (Thread *) _owner ; |
|
2762 |
if (ox == NULL) { |
|
2763 |
ox = (Thread *) Atomic::cmpxchg_ptr (Self, &_owner, NULL) ; |
|
2764 |
if (ox == NULL) { |
|
2765 |
// The CAS succeeded -- this thread acquired ownership |
|
2766 |
// Take care of some bookkeeping to exit spin state. |
|
2767 |
if (sss && _succ == Self) { |
|
2768 |
_succ = NULL ; |
|
2769 |
} |
|
2770 |
if (MaxSpin > 0) Adjust (&_Spinner, -1) ; |
|
2771 |
||
2772 |
// Increase _SpinDuration : |
|
2773 |
// The spin was successful (profitable) so we tend toward |
|
2774 |
// longer spin attempts in the future. |
|
2775 |
// CONSIDER: factor "ctr" into the _SpinDuration adjustment. |
|
2776 |
// If we acquired the lock early in the spin cycle it |
|
2777 |
// makes sense to increase _SpinDuration proportionally. |
|
2778 |
// Note that we don't clamp SpinDuration precisely at SpinLimit. |
|
2779 |
int x = _SpinDuration ; |
|
2780 |
if (x < Knob_SpinLimit) { |
|
2781 |
if (x < Knob_Poverty) x = Knob_Poverty ; |
|
2782 |
_SpinDuration = x + Knob_Bonus ; |
|
2783 |
} |
|
2784 |
return 1 ; |
|
2785 |
} |
|
2786 |
||
2787 |
// The CAS failed ... we can take any of the following actions: |
|
2788 |
// * penalize: ctr -= Knob_CASPenalty |
|
2789 |
// * exit spin with prejudice -- goto Abort; |
|
2790 |
// * exit spin without prejudice. |
|
2791 |
// * Since CAS is high-latency, retry again immediately. |
|
2792 |
prv = ox ; |
|
2793 |
TEVENT (Spin: cas failed) ; |
|
2794 |
if (caspty == -2) break ; |
|
2795 |
if (caspty == -1) goto Abort ; |
|
2796 |
ctr -= caspty ; |
|
2797 |
continue ; |
|
2798 |
} |
|
2799 |
||
2800 |
// Did lock ownership change hands ? |
|
2801 |
if (ox != prv && prv != NULL ) { |
|
2802 |
TEVENT (spin: Owner changed) |
|
2803 |
if (oxpty == -2) break ; |
|
2804 |
if (oxpty == -1) goto Abort ; |
|
2805 |
ctr -= oxpty ; |
|
2806 |
} |
|
2807 |
prv = ox ; |
|
2808 |
||
2809 |
// Abort the spin if the owner is not executing. |
|
2810 |
// The owner must be executing in order to drop the lock. |
|
2811 |
// Spinning while the owner is OFFPROC is idiocy. |
|
2812 |
// Consider: ctr -= RunnablePenalty ; |
|
2813 |
if (Knob_OState && NotRunnable (Self, ox)) { |
|
2814 |
TEVENT (Spin abort - notrunnable); |
|
2815 |
goto Abort ; |
|
2816 |
} |
|
2817 |
if (sss && _succ == NULL ) _succ = Self ; |
|
2818 |
} |
|
2819 |
||
2820 |
// Spin failed with prejudice -- reduce _SpinDuration. |
|
2821 |
// TODO: Use an AIMD-like policy to adjust _SpinDuration. |
|
2822 |
// AIMD is globally stable. |
|
2823 |
TEVENT (Spin failure) ; |
|
2824 |
{ |
|
2825 |
int x = _SpinDuration ; |
|
2826 |
if (x > 0) { |
|
2827 |
// Consider an AIMD scheme like: x -= (x >> 3) + 100 |
|
2828 |
// This is globally sample and tends to damp the response. |
|
2829 |
x -= Knob_Penalty ; |
|
2830 |
if (x < 0) x = 0 ; |
|
2831 |
_SpinDuration = x ; |
|
2832 |
} |
|
2833 |
} |
|
2834 |
||
2835 |
Abort: |
|
2836 |
if (MaxSpin >= 0) Adjust (&_Spinner, -1) ; |
|
2837 |
if (sss && _succ == Self) { |
|
2838 |
_succ = NULL ; |
|
2839 |
// Invariant: after setting succ=null a contending thread |
|
2840 |
// must recheck-retry _owner before parking. This usually happens |
|
2841 |
// in the normal usage of TrySpin(), but it's safest |
|
2842 |
// to make TrySpin() as foolproof as possible. |
|
2843 |
OrderAccess::fence() ; |
|
2844 |
if (TryLock(Self) > 0) return 1 ; |
|
2845 |
} |
|
2846 |
return 0 ; |
|
2847 |
} |
|
2848 |
||
2849 |
#define TrySpin TrySpin_VaryDuration |
|
2850 |
||
2851 |
static void DeferredInitialize () { |
|
2852 |
if (InitDone > 0) return ; |
|
2853 |
if (Atomic::cmpxchg (-1, &InitDone, 0) != 0) { |
|
2854 |
while (InitDone != 1) ; |
|
2855 |
return ; |
|
2856 |
} |
|
2857 |
||
2858 |
// One-shot global initialization ... |
|
2859 |
// The initialization is idempotent, so we don't need locks. |
|
2860 |
// In the future consider doing this via os::init_2(). |
|
2861 |
// SyncKnobs consist of <Key>=<Value> pairs in the style |
|
2862 |
// of environment variables. Start by converting ':' to NUL. |
|
2863 |
||
2864 |
if (SyncKnobs == NULL) SyncKnobs = "" ; |
|
2865 |
||
2866 |
size_t sz = strlen (SyncKnobs) ; |
|
2867 |
char * knobs = (char *) malloc (sz + 2) ; |
|
2868 |
if (knobs == NULL) { |
|
2869 |
vm_exit_out_of_memory (sz + 2, "Parse SyncKnobs") ; |
|
2870 |
guarantee (0, "invariant") ; |
|
2871 |
} |
|
2872 |
strcpy (knobs, SyncKnobs) ; |
|
2873 |
knobs[sz+1] = 0 ; |
|
2874 |
for (char * p = knobs ; *p ; p++) { |
|
2875 |
if (*p == ':') *p = 0 ; |
|
2876 |
} |
|
2877 |
||
2878 |
#define SETKNOB(x) { Knob_##x = kvGetInt (knobs, #x, Knob_##x); } |
|
2879 |
SETKNOB(ReportSettings) ; |
|
2880 |
SETKNOB(Verbose) ; |
|
2881 |
SETKNOB(FixedSpin) ; |
|
2882 |
SETKNOB(SpinLimit) ; |
|
2883 |
SETKNOB(SpinBase) ; |
|
2884 |
SETKNOB(SpinBackOff); |
|
2885 |
SETKNOB(CASPenalty) ; |
|
2886 |
SETKNOB(OXPenalty) ; |
|
2887 |
SETKNOB(LogSpins) ; |
|
2888 |
SETKNOB(SpinSetSucc) ; |
|
2889 |
SETKNOB(SuccEnabled) ; |
|
2890 |
SETKNOB(SuccRestrict) ; |
|
2891 |
SETKNOB(Penalty) ; |
|
2892 |
SETKNOB(Bonus) ; |
|
2893 |
SETKNOB(BonusB) ; |
|
2894 |
SETKNOB(Poverty) ; |
|
2895 |
SETKNOB(SpinAfterFutile) ; |
|
2896 |
SETKNOB(UsePause) ; |
|
2897 |
SETKNOB(SpinEarly) ; |
|
2898 |
SETKNOB(OState) ; |
|
2899 |
SETKNOB(MaxSpinners) ; |
|
2900 |
SETKNOB(PreSpin) ; |
|
2901 |
SETKNOB(ExitPolicy) ; |
|
2902 |
SETKNOB(QMode); |
|
2903 |
SETKNOB(ResetEvent) ; |
|
2904 |
SETKNOB(MoveNotifyee) ; |
|
2905 |
SETKNOB(FastHSSEC) ; |
|
2906 |
#undef SETKNOB |
|
2907 |
||
2908 |
if (os::is_MP()) { |
|
2909 |
BackOffMask = (1 << Knob_SpinBackOff) - 1 ; |
|
2910 |
if (Knob_ReportSettings) ::printf ("BackOffMask=%X\n", BackOffMask) ; |
|
2911 |
// CONSIDER: BackOffMask = ROUNDUP_NEXT_POWER2 (ncpus-1) |
|
2912 |
} else { |
|
2913 |
Knob_SpinLimit = 0 ; |
|
2914 |
Knob_SpinBase = 0 ; |
|
2915 |
Knob_PreSpin = 0 ; |
|
2916 |
Knob_FixedSpin = -1 ; |
|
2917 |
} |
|
2918 |
||
2919 |
if (Knob_LogSpins == 0) { |
|
2920 |
ObjectSynchronizer::_sync_FailedSpins = NULL ; |
|
2921 |
} |
|
2922 |
||
2923 |
free (knobs) ; |
|
2924 |
OrderAccess::fence() ; |
|
2925 |
InitDone = 1 ; |
|
2926 |
} |
|
2927 |
||
2928 |
// Theory of operations -- Monitors lists, thread residency, etc: |
|
2929 |
// |
|
2930 |
// * A thread acquires ownership of a monitor by successfully |
|
2931 |
// CAS()ing the _owner field from null to non-null. |
|
2932 |
// |
|
2933 |
// * Invariant: A thread appears on at most one monitor list -- |
|
2934 |
// cxq, EntryList or WaitSet -- at any one time. |
|
2935 |
// |
|
2936 |
// * Contending threads "push" themselves onto the cxq with CAS |
|
2937 |
// and then spin/park. |
|
2938 |
// |
|
2939 |
// * After a contending thread eventually acquires the lock it must |
|
2940 |
// dequeue itself from either the EntryList or the cxq. |
|
2941 |
// |
|
2942 |
// * The exiting thread identifies and unparks an "heir presumptive" |
|
2943 |
// tentative successor thread on the EntryList. Critically, the |
|
2944 |
// exiting thread doesn't unlink the successor thread from the EntryList. |
|
2945 |
// After having been unparked, the wakee will recontend for ownership of |
|
2946 |
// the monitor. The successor (wakee) will either acquire the lock or |
|
2947 |
// re-park itself. |
|
2948 |
// |
|
2949 |
// Succession is provided for by a policy of competitive handoff. |
|
2950 |
// The exiting thread does _not_ grant or pass ownership to the |
|
2951 |
// successor thread. (This is also referred to as "handoff" succession"). |
|
2952 |
// Instead the exiting thread releases ownership and possibly wakes |
|
2953 |
// a successor, so the successor can (re)compete for ownership of the lock. |
|
2954 |
// If the EntryList is empty but the cxq is populated the exiting |
|
2955 |
// thread will drain the cxq into the EntryList. It does so by |
|
2956 |
// by detaching the cxq (installing null with CAS) and folding |
|
2957 |
// the threads from the cxq into the EntryList. The EntryList is |
|
2958 |
// doubly linked, while the cxq is singly linked because of the |
|
2959 |
// CAS-based "push" used to enqueue recently arrived threads (RATs). |
|
2960 |
// |
|
2961 |
// * Concurrency invariants: |
|
2962 |
// |
|
2963 |
// -- only the monitor owner may access or mutate the EntryList. |
|
2964 |
// The mutex property of the monitor itself protects the EntryList |
|
2965 |
// from concurrent interference. |
|
2966 |
// -- Only the monitor owner may detach the cxq. |
|
2967 |
// |
|
2968 |
// * The monitor entry list operations avoid locks, but strictly speaking |
|
2969 |
// they're not lock-free. Enter is lock-free, exit is not. |
|
2970 |
// See http://j2se.east/~dice/PERSIST/040825-LockFreeQueues.html |
|
2971 |
// |
|
2972 |
// * The cxq can have multiple concurrent "pushers" but only one concurrent |
|
2973 |
// detaching thread. This mechanism is immune from the ABA corruption. |
|
2974 |
// More precisely, the CAS-based "push" onto cxq is ABA-oblivious. |
|
2975 |
// |
|
2976 |
// * Taken together, the cxq and the EntryList constitute or form a |
|
2977 |
// single logical queue of threads stalled trying to acquire the lock. |
|
2978 |
// We use two distinct lists to improve the odds of a constant-time |
|
2979 |
// dequeue operation after acquisition (in the ::enter() epilog) and |
|
2980 |
// to reduce heat on the list ends. (c.f. Michael Scott's "2Q" algorithm). |
|
2981 |
// A key desideratum is to minimize queue & monitor metadata manipulation |
|
2982 |
// that occurs while holding the monitor lock -- that is, we want to |
|
2983 |
// minimize monitor lock holds times. Note that even a small amount of |
|
2984 |
// fixed spinning will greatly reduce the # of enqueue-dequeue operations |
|
2985 |
// on EntryList|cxq. That is, spinning relieves contention on the "inner" |
|
2986 |
// locks and monitor metadata. |
|
2987 |
// |
|
2988 |
// Cxq points to the the set of Recently Arrived Threads attempting entry. |
|
2989 |
// Because we push threads onto _cxq with CAS, the RATs must take the form of |
|
2990 |
// a singly-linked LIFO. We drain _cxq into EntryList at unlock-time when |
|
2991 |
// the unlocking thread notices that EntryList is null but _cxq is != null. |
|
2992 |
// |
|
2993 |
// The EntryList is ordered by the prevailing queue discipline and |
|
2994 |
// can be organized in any convenient fashion, such as a doubly-linked list or |
|
2995 |
// a circular doubly-linked list. Critically, we want insert and delete operations |
|
2996 |
// to operate in constant-time. If we need a priority queue then something akin |
|
2997 |
// to Solaris' sleepq would work nicely. Viz., |
|
2998 |
// http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c. |
|
2999 |
// Queue discipline is enforced at ::exit() time, when the unlocking thread |
|
3000 |
// drains the cxq into the EntryList, and orders or reorders the threads on the |
|
3001 |
// EntryList accordingly. |
|
3002 |
// |
|
3003 |
// Barring "lock barging", this mechanism provides fair cyclic ordering, |
|
3004 |
// somewhat similar to an elevator-scan. |
|
3005 |
// |
|
3006 |
// * The monitor synchronization subsystem avoids the use of native |
|
3007 |
// synchronization primitives except for the narrow platform-specific |
|
3008 |
// park-unpark abstraction. See the comments in os_solaris.cpp regarding |
|
3009 |
// the semantics of park-unpark. Put another way, this monitor implementation |
|
3010 |
// depends only on atomic operations and park-unpark. The monitor subsystem |
|
3011 |
// manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the |
|
3012 |
// underlying OS manages the READY<->RUN transitions. |
|
3013 |
// |
|
3014 |
// * Waiting threads reside on the WaitSet list -- wait() puts |
|
3015 |
// the caller onto the WaitSet. |
|
3016 |
// |
|
3017 |
// * notify() or notifyAll() simply transfers threads from the WaitSet to |
|
3018 |
// either the EntryList or cxq. Subsequent exit() operations will |
|
3019 |
// unpark the notifyee. Unparking a notifee in notify() is inefficient - |
|
3020 |
// it's likely the notifyee would simply impale itself on the lock held |
|
3021 |
// by the notifier. |
|
3022 |
// |
|
3023 |
// * An interesting alternative is to encode cxq as (List,LockByte) where |
|
3024 |
// the LockByte is 0 iff the monitor is owned. _owner is simply an auxiliary |
|
3025 |
// variable, like _recursions, in the scheme. The threads or Events that form |
|
3026 |
// the list would have to be aligned in 256-byte addresses. A thread would |
|
3027 |
// try to acquire the lock or enqueue itself with CAS, but exiting threads |
|
3028 |
// could use a 1-0 protocol and simply STB to set the LockByte to 0. |
|
3029 |
// Note that is is *not* word-tearing, but it does presume that full-word |
|
3030 |
// CAS operations are coherent with intermix with STB operations. That's true |
|
3031 |
// on most common processors. |
|
3032 |
// |
|
3033 |
// * See also http://blogs.sun.com/dave |
|
3034 |
||
3035 |
||
3036 |
void ATTR ObjectMonitor::EnterI (TRAPS) { |
|
3037 |
Thread * Self = THREAD ; |
|
3038 |
assert (Self->is_Java_thread(), "invariant") ; |
|
3039 |
assert (((JavaThread *) Self)->thread_state() == _thread_blocked , "invariant") ; |
|
3040 |
||
3041 |
// Try the lock - TATAS |
|
3042 |
if (TryLock (Self) > 0) { |
|
3043 |
assert (_succ != Self , "invariant") ; |
|
3044 |
assert (_owner == Self , "invariant") ; |
|
3045 |
assert (_Responsible != Self , "invariant") ; |
|
3046 |
return ; |
|
3047 |
} |
|
3048 |
||
3049 |
DeferredInitialize () ; |
|
3050 |
||
3051 |
// We try one round of spinning *before* enqueueing Self. |
|
3052 |
// |
|
3053 |
// If the _owner is ready but OFFPROC we could use a YieldTo() |
|
3054 |
// operation to donate the remainder of this thread's quantum |
|
3055 |
// to the owner. This has subtle but beneficial affinity |
|
3056 |
// effects. |
|
3057 |
||
3058 |
if (TrySpin (Self) > 0) { |
|
3059 |
assert (_owner == Self , "invariant") ; |
|
3060 |
assert (_succ != Self , "invariant") ; |
|
3061 |
assert (_Responsible != Self , "invariant") ; |
|
3062 |
return ; |
|
3063 |
} |
|
3064 |
||
3065 |
// The Spin failed -- Enqueue and park the thread ... |
|
3066 |
assert (_succ != Self , "invariant") ; |
|
3067 |
assert (_owner != Self , "invariant") ; |
|
3068 |
assert (_Responsible != Self , "invariant") ; |
|
3069 |
||
3070 |
// Enqueue "Self" on ObjectMonitor's _cxq. |
|
3071 |
// |
|
3072 |
// Node acts as a proxy for Self. |
|
3073 |
// As an aside, if were to ever rewrite the synchronization code mostly |
|
3074 |
// in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class |
|
3075 |
// Java objects. This would avoid awkward lifecycle and liveness issues, |
|
3076 |
// as well as eliminate a subset of ABA issues. |
|
3077 |
// TODO: eliminate ObjectWaiter and enqueue either Threads or Events. |
|
3078 |
// |
|
3079 |
||
3080 |
ObjectWaiter node(Self) ; |
|
3081 |
Self->_ParkEvent->reset() ; |
|
3082 |
node._prev = (ObjectWaiter *) 0xBAD ; |
|
3083 |
node.TState = ObjectWaiter::TS_CXQ ; |
|
3084 |
||
3085 |
// Push "Self" onto the front of the _cxq. |
|
3086 |
// Once on cxq/EntryList, Self stays on-queue until it acquires the lock. |
|
3087 |
// Note that spinning tends to reduce the rate at which threads |
|
3088 |
// enqueue and dequeue on EntryList|cxq. |
|
3089 |
ObjectWaiter * nxt ; |
|
3090 |
for (;;) { |
|
3091 |
node._next = nxt = _cxq ; |
|
3092 |
if (Atomic::cmpxchg_ptr (&node, &_cxq, nxt) == nxt) break ; |
|
3093 |
||
3094 |
// Interference - the CAS failed because _cxq changed. Just retry. |
|
3095 |
// As an optional optimization we retry the lock. |
|
3096 |
if (TryLock (Self) > 0) { |
|
3097 |
assert (_succ != Self , "invariant") ; |
|
3098 |
assert (_owner == Self , "invariant") ; |
|
3099 |
assert (_Responsible != Self , "invariant") ; |
|
3100 |
return ; |
|
3101 |
} |
|
3102 |
} |
|
3103 |
||
3104 |
// Check for cxq|EntryList edge transition to non-null. This indicates |
|
3105 |
// the onset of contention. While contention persists exiting threads |
|
3106 |
// will use a ST:MEMBAR:LD 1-1 exit protocol. When contention abates exit |
|
3107 |
// operations revert to the faster 1-0 mode. This enter operation may interleave |
|
3108 |
// (race) a concurrent 1-0 exit operation, resulting in stranding, so we |
|
3109 |
// arrange for one of the contending thread to use a timed park() operations |
|
3110 |
// to detect and recover from the race. (Stranding is form of progress failure |
|
3111 |
// where the monitor is unlocked but all the contending threads remain parked). |
|
3112 |
// That is, at least one of the contended threads will periodically poll _owner. |
|
3113 |
// One of the contending threads will become the designated "Responsible" thread. |
|
3114 |
// The Responsible thread uses a timed park instead of a normal indefinite park |
|
3115 |
// operation -- it periodically wakes and checks for and recovers from potential |
|
3116 |
// strandings admitted by 1-0 exit operations. We need at most one Responsible |
|
3117 |
// thread per-monitor at any given moment. Only threads on cxq|EntryList may |
|
3118 |
// be responsible for a monitor. |
|
3119 |
// |
|
3120 |
// Currently, one of the contended threads takes on the added role of "Responsible". |
|
3121 |
// A viable alternative would be to use a dedicated "stranding checker" thread |
|
3122 |
// that periodically iterated over all the threads (or active monitors) and unparked |
|
3123 |
// successors where there was risk of stranding. This would help eliminate the |
|
3124 |
// timer scalability issues we see on some platforms as we'd only have one thread |
|
3125 |
// -- the checker -- parked on a timer. |
|
3126 |
||
3127 |
if ((SyncFlags & 16) == 0 && nxt == NULL && _EntryList == NULL) { |
|
3128 |
// Try to assume the role of responsible thread for the monitor. |
|
3129 |
// CONSIDER: ST vs CAS vs { if (Responsible==null) Responsible=Self } |
|
3130 |
Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ; |
|
3131 |
} |
|
3132 |
||
3133 |
// The lock have been released while this thread was occupied queueing |
|
3134 |
// itself onto _cxq. To close the race and avoid "stranding" and |
|
3135 |
// progress-liveness failure we must resample-retry _owner before parking. |
|
3136 |
// Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner. |
|
3137 |
// In this case the ST-MEMBAR is accomplished with CAS(). |
|
3138 |
// |
|
3139 |
// TODO: Defer all thread state transitions until park-time. |
|
3140 |
// Since state transitions are heavy and inefficient we'd like |
|
3141 |
// to defer the state transitions until absolutely necessary, |
|
3142 |
// and in doing so avoid some transitions ... |
|
3143 |
||
3144 |
TEVENT (Inflated enter - Contention) ; |
|
3145 |
int nWakeups = 0 ; |
|
3146 |
int RecheckInterval = 1 ; |
|
3147 |
||
3148 |
for (;;) { |
|
3149 |
||
3150 |
if (TryLock (Self) > 0) break ; |
|
3151 |
assert (_owner != Self, "invariant") ; |
|
3152 |
||
3153 |
if ((SyncFlags & 2) && _Responsible == NULL) { |
|
3154 |
Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ; |
|
3155 |
} |
|
3156 |
||
3157 |
// park self |
|
3158 |
if (_Responsible == Self || (SyncFlags & 1)) { |
|
3159 |
TEVENT (Inflated enter - park TIMED) ; |
|
3160 |
Self->_ParkEvent->park ((jlong) RecheckInterval) ; |
|
3161 |
// Increase the RecheckInterval, but clamp the value. |
|
3162 |
RecheckInterval *= 8 ; |
|
3163 |
if (RecheckInterval > 1000) RecheckInterval = 1000 ; |
|
3164 |
} else { |
|
3165 |
TEVENT (Inflated enter - park UNTIMED) ; |
|
3166 |
Self->_ParkEvent->park() ; |
|
3167 |
} |
|
3168 |
||
3169 |
if (TryLock(Self) > 0) break ; |
|
3170 |
||
3171 |
// The lock is still contested. |
|
3172 |
// Keep a tally of the # of futile wakeups. |
|
3173 |
// Note that the counter is not protected by a lock or updated by atomics. |
|
3174 |
// That is by design - we trade "lossy" counters which are exposed to |
|
3175 |
// races during updates for a lower probe effect. |
|
3176 |
TEVENT (Inflated enter - Futile wakeup) ; |
|
3177 |
if (ObjectSynchronizer::_sync_FutileWakeups != NULL) { |
|
3178 |
ObjectSynchronizer::_sync_FutileWakeups->inc() ; |
|
3179 |
} |
|
3180 |
++ nWakeups ; |
|
3181 |
||
3182 |
// Assuming this is not a spurious wakeup we'll normally find _succ == Self. |
|
3183 |
// We can defer clearing _succ until after the spin completes |
|
3184 |
// TrySpin() must tolerate being called with _succ == Self. |
|
3185 |
// Try yet another round of adaptive spinning. |
|
3186 |
if ((Knob_SpinAfterFutile & 1) && TrySpin (Self) > 0) break ; |
|
3187 |
||
3188 |
// We can find that we were unpark()ed and redesignated _succ while |
|
3189 |
// we were spinning. That's harmless. If we iterate and call park(), |
|
3190 |
// park() will consume the event and return immediately and we'll |
|
3191 |
// just spin again. This pattern can repeat, leaving _succ to simply |
|
3192 |
// spin on a CPU. Enable Knob_ResetEvent to clear pending unparks(). |
|
3193 |
// Alternately, we can sample fired() here, and if set, forgo spinning |
|
3194 |
// in the next iteration. |
|
3195 |
||
3196 |
if ((Knob_ResetEvent & 1) && Self->_ParkEvent->fired()) { |
|
3197 |
Self->_ParkEvent->reset() ; |
|
3198 |
OrderAccess::fence() ; |
|
3199 |
} |
|
3200 |
if (_succ == Self) _succ = NULL ; |
|
3201 |
||
3202 |
// Invariant: after clearing _succ a thread *must* retry _owner before parking. |
|
3203 |
OrderAccess::fence() ; |
|
3204 |
} |
|
3205 |
||
3206 |
// Egress : |
|
3207 |
// Self has acquired the lock -- Unlink Self from the cxq or EntryList. |
|
3208 |
// Normally we'll find Self on the EntryList . |
|
3209 |
// From the perspective of the lock owner (this thread), the |
|
3210 |
// EntryList is stable and cxq is prepend-only. |
|
3211 |
// The head of cxq is volatile but the interior is stable. |
|
3212 |
// In addition, Self.TState is stable. |
|
3213 |
||
3214 |
assert (_owner == Self , "invariant") ; |
|
3215 |
assert (object() != NULL , "invariant") ; |
|
3216 |
// I'd like to write: |
|
3217 |
// guarantee (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ; |
|
3218 |
// but as we're at a safepoint that's not safe. |
|
3219 |
||
3220 |
UnlinkAfterAcquire (Self, &node) ; |
|
3221 |
if (_succ == Self) _succ = NULL ; |
|
3222 |
||
3223 |
assert (_succ != Self, "invariant") ; |
|
3224 |
if (_Responsible == Self) { |
|
3225 |
_Responsible = NULL ; |
|
3226 |
// Dekker pivot-point. |
|
3227 |
// Consider OrderAccess::storeload() here |
|
3228 |
||
3229 |
// We may leave threads on cxq|EntryList without a designated |
|
3230 |
// "Responsible" thread. This is benign. When this thread subsequently |
|
3231 |
// exits the monitor it can "see" such preexisting "old" threads -- |
|
3232 |
// threads that arrived on the cxq|EntryList before the fence, above -- |
|
3233 |
// by LDing cxq|EntryList. Newly arrived threads -- that is, threads |
|
3234 |
// that arrive on cxq after the ST:MEMBAR, above -- will set Responsible |
|
3235 |
// non-null and elect a new "Responsible" timer thread. |
|
3236 |
// |
|
3237 |
// This thread executes: |
|
3238 |
// ST Responsible=null; MEMBAR (in enter epilog - here) |
|
3239 |
// LD cxq|EntryList (in subsequent exit) |
|
3240 |
// |
|
3241 |
// Entering threads in the slow/contended path execute: |
|
3242 |
// ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog) |
|
3243 |
// The (ST cxq; MEMBAR) is accomplished with CAS(). |
|
3244 |
// |
|
3245 |
// The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent |
|
3246 |
// exit operation from floating above the ST Responsible=null. |
|
3247 |
// |
|
3248 |
// In *practice* however, EnterI() is always followed by some atomic |
|
3249 |
// operation such as the decrement of _count in ::enter(). Those atomics |
|
3250 |
// obviate the need for the explicit MEMBAR, above. |
|
3251 |
} |
|
3252 |
||
3253 |
// We've acquired ownership with CAS(). |
|
3254 |
// CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics. |
|
3255 |
// But since the CAS() this thread may have also stored into _succ, |
|
3256 |
// EntryList, cxq or Responsible. These meta-data updates must be |
|
3257 |
// visible __before this thread subsequently drops the lock. |
|
3258 |
// Consider what could occur if we didn't enforce this constraint -- |
|
3259 |
// STs to monitor meta-data and user-data could reorder with (become |
|
3260 |
// visible after) the ST in exit that drops ownership of the lock. |
|
3261 |
// Some other thread could then acquire the lock, but observe inconsistent |
|
3262 |
// or old monitor meta-data and heap data. That violates the JMM. |
|
3263 |
// To that end, the 1-0 exit() operation must have at least STST|LDST |
|
3264 |
// "release" barrier semantics. Specifically, there must be at least a |
|
3265 |
// STST|LDST barrier in exit() before the ST of null into _owner that drops |
|
3266 |
// the lock. The barrier ensures that changes to monitor meta-data and data |
|
3267 |
// protected by the lock will be visible before we release the lock, and |
|
3268 |
// therefore before some other thread (CPU) has a chance to acquire the lock. |
|
3269 |
// See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html. |
|
3270 |
// |
|
3271 |
// Critically, any prior STs to _succ or EntryList must be visible before |
|
3272 |
// the ST of null into _owner in the *subsequent* (following) corresponding |
|
3273 |
// monitorexit. Recall too, that in 1-0 mode monitorexit does not necessarily |
|
3274 |
// execute a serializing instruction. |
|
3275 |
||
3276 |
if (SyncFlags & 8) { |
|
3277 |
OrderAccess::fence() ; |
|
3278 |
} |
|
3279 |
return ; |
|
3280 |
} |
|
3281 |
||
3282 |
// ExitSuspendEquivalent: |
|
3283 |
// A faster alternate to handle_special_suspend_equivalent_condition() |
|
3284 |
// |
|
3285 |
// handle_special_suspend_equivalent_condition() unconditionally |
|
3286 |
// acquires the SR_lock. On some platforms uncontended MutexLocker() |
|
3287 |
// operations have high latency. Note that in ::enter() we call HSSEC |
|
3288 |
// while holding the monitor, so we effectively lengthen the critical sections. |
|
3289 |
// |
|
3290 |
// There are a number of possible solutions: |
|
3291 |
// |
|
3292 |
// A. To ameliorate the problem we might also defer state transitions |
|
3293 |
// to as late as possible -- just prior to parking. |
|
3294 |
// Given that, we'd call HSSEC after having returned from park(), |
|
3295 |
// but before attempting to acquire the monitor. This is only a |
|
3296 |
// partial solution. It avoids calling HSSEC while holding the |
|
3297 |
// monitor (good), but it still increases successor reacquisition latency -- |
|
3298 |
// the interval between unparking a successor and the time the successor |
|
3299 |
// resumes and retries the lock. See ReenterI(), which defers state transitions. |
|
3300 |
// If we use this technique we can also avoid EnterI()-exit() loop |
|
3301 |
// in ::enter() where we iteratively drop the lock and then attempt |
|
3302 |
// to reacquire it after suspending. |
|
3303 |
// |
|
3304 |
// B. In the future we might fold all the suspend bits into a |
|
3305 |
// composite per-thread suspend flag and then update it with CAS(). |
|
3306 |
// Alternately, a Dekker-like mechanism with multiple variables |
|
3307 |
// would suffice: |
|
3308 |
// ST Self->_suspend_equivalent = false |
|
3309 |
// MEMBAR |
|
3310 |
// LD Self_>_suspend_flags |
|
3311 |
// |
|
3312 |
||
3313 |
||
3314 |
bool ObjectMonitor::ExitSuspendEquivalent (JavaThread * jSelf) { |
|
3315 |
int Mode = Knob_FastHSSEC ; |
|
3316 |
if (Mode && !jSelf->is_external_suspend()) { |
|
3317 |
assert (jSelf->is_suspend_equivalent(), "invariant") ; |
|
3318 |
jSelf->clear_suspend_equivalent() ; |
|
3319 |
if (2 == Mode) OrderAccess::storeload() ; |
|
3320 |
if (!jSelf->is_external_suspend()) return false ; |
|
3321 |
// We raced a suspension -- fall thru into the slow path |
|
3322 |
TEVENT (ExitSuspendEquivalent - raced) ; |
|
3323 |
jSelf->set_suspend_equivalent() ; |
|
3324 |
} |
|
3325 |
return jSelf->handle_special_suspend_equivalent_condition() ; |
|
3326 |
} |
|
3327 |
||
3328 |
||
3329 |
// ReenterI() is a specialized inline form of the latter half of the |
|
3330 |
// contended slow-path from EnterI(). We use ReenterI() only for |
|
3331 |
// monitor reentry in wait(). |
|
3332 |
// |
|
3333 |
// In the future we should reconcile EnterI() and ReenterI(), adding |
|
3334 |
// Knob_Reset and Knob_SpinAfterFutile support and restructuring the |
|
3335 |
// loop accordingly. |
|
3336 |
||
3337 |
void ATTR ObjectMonitor::ReenterI (Thread * Self, ObjectWaiter * SelfNode) { |
|
3338 |
assert (Self != NULL , "invariant") ; |
|
3339 |
assert (SelfNode != NULL , "invariant") ; |
|
3340 |
assert (SelfNode->_thread == Self , "invariant") ; |
|
3341 |
assert (_waiters > 0 , "invariant") ; |
|
3342 |
assert (((oop)(object()))->mark() == markOopDesc::encode(this) , "invariant") ; |
|
3343 |
assert (((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ; |
|
3344 |
JavaThread * jt = (JavaThread *) Self ; |
|
3345 |
||
3346 |
int nWakeups = 0 ; |
|
3347 |
for (;;) { |
|
3348 |
ObjectWaiter::TStates v = SelfNode->TState ; |
|
3349 |
guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ; |
|
3350 |
assert (_owner != Self, "invariant") ; |
|
3351 |
||
3352 |
if (TryLock (Self) > 0) break ; |
|
3353 |
if (TrySpin (Self) > 0) break ; |
|
3354 |
||
3355 |
TEVENT (Wait Reentry - parking) ; |
|
3356 |
||
3357 |
// State transition wrappers around park() ... |
|
3358 |
// ReenterI() wisely defers state transitions until |
|
3359 |
// it's clear we must park the thread. |
|
3360 |
{ |
|
3361 |
OSThreadContendState osts(Self->osthread()); |
|
3362 |
ThreadBlockInVM tbivm(jt); |
|
3363 |
||
3364 |
// cleared by handle_special_suspend_equivalent_condition() |
|
3365 |
// or java_suspend_self() |
|
3366 |
jt->set_suspend_equivalent(); |
|
3367 |
if (SyncFlags & 1) { |
|
3368 |
Self->_ParkEvent->park ((jlong)1000) ; |
|
3369 |
} else { |
|
3370 |
Self->_ParkEvent->park () ; |
|
3371 |
} |
|
3372 |
||
3373 |
// were we externally suspended while we were waiting? |
|
3374 |
for (;;) { |
|
3375 |
if (!ExitSuspendEquivalent (jt)) break ; |
|
3376 |
if (_succ == Self) { _succ = NULL; OrderAccess::fence(); } |
|
3377 |
jt->java_suspend_self(); |
|
3378 |
jt->set_suspend_equivalent(); |
|
3379 |
} |
|
3380 |
} |
|
3381 |
||
3382 |
// Try again, but just so we distinguish between futile wakeups and |
|
3383 |
// successful wakeups. The following test isn't algorithmically |
|
3384 |
// necessary, but it helps us maintain sensible statistics. |
|
3385 |
if (TryLock(Self) > 0) break ; |
|
3386 |
||
3387 |
// The lock is still contested. |
|
3388 |
// Keep a tally of the # of futile wakeups. |
|
3389 |
// Note that the counter is not protected by a lock or updated by atomics. |
|
3390 |
// That is by design - we trade "lossy" counters which are exposed to |
|
3391 |
// races during updates for a lower probe effect. |
|
3392 |
TEVENT (Wait Reentry - futile wakeup) ; |
|
3393 |
++ nWakeups ; |
|
3394 |
||
3395 |
// Assuming this is not a spurious wakeup we'll normally |
|
3396 |
// find that _succ == Self. |
|
3397 |
if (_succ == Self) _succ = NULL ; |
|
3398 |
||
3399 |
// Invariant: after clearing _succ a contending thread |
|
3400 |
// *must* retry _owner before parking. |
|
3401 |
OrderAccess::fence() ; |
|
3402 |
||
3403 |
if (ObjectSynchronizer::_sync_FutileWakeups != NULL) { |
|
3404 |
ObjectSynchronizer::_sync_FutileWakeups->inc() ; |
|
3405 |
} |
|
3406 |
} |
|
3407 |
||
3408 |
// Self has acquired the lock -- Unlink Self from the cxq or EntryList . |
|
3409 |
// Normally we'll find Self on the EntryList. |
|
3410 |
// Unlinking from the EntryList is constant-time and atomic-free. |
|
3411 |
// From the perspective of the lock owner (this thread), the |
|
3412 |
// EntryList is stable and cxq is prepend-only. |
|
3413 |
// The head of cxq is volatile but the interior is stable. |
|
3414 |
// In addition, Self.TState is stable. |
|
3415 |
||
3416 |
assert (_owner == Self, "invariant") ; |
|
3417 |
assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ; |
|
3418 |
UnlinkAfterAcquire (Self, SelfNode) ; |
|
3419 |
if (_succ == Self) _succ = NULL ; |
|
3420 |
assert (_succ != Self, "invariant") ; |
|
3421 |
SelfNode->TState = ObjectWaiter::TS_RUN ; |
|
3422 |
OrderAccess::fence() ; // see comments at the end of EnterI() |
|
3423 |
} |
|
3424 |
||
3425 |
bool ObjectMonitor::try_enter(Thread* THREAD) { |
|
3426 |
if (THREAD != _owner) { |
|
3427 |
if (THREAD->is_lock_owned ((address)_owner)) { |
|
3428 |
assert(_recursions == 0, "internal state error"); |
|
3429 |
_owner = THREAD ; |
|
3430 |
_recursions = 1 ; |
|
3431 |
OwnerIsThread = 1 ; |
|
3432 |
return true; |
|
3433 |
} |
|
3434 |
if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) { |
|
3435 |
return false; |
|
3436 |
} |
|
3437 |
return true; |
|
3438 |
} else { |
|
3439 |
_recursions++; |
|
3440 |
return true; |
|
3441 |
} |
|
3442 |
} |
|
3443 |
||
3444 |
void ATTR ObjectMonitor::enter(TRAPS) { |
|
3445 |
// The following code is ordered to check the most common cases first |
|
3446 |
// and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors. |
|
3447 |
Thread * const Self = THREAD ; |
|
3448 |
void * cur ; |
|
3449 |
||
3450 |
cur = Atomic::cmpxchg_ptr (Self, &_owner, NULL) ; |
|
3451 |
if (cur == NULL) { |
|
3452 |
// Either ASSERT _recursions == 0 or explicitly set _recursions = 0. |
|
3453 |
assert (_recursions == 0 , "invariant") ; |
|
3454 |
assert (_owner == Self, "invariant") ; |
|
3455 |
// CONSIDER: set or assert OwnerIsThread == 1 |
|
3456 |
return ; |
|
3457 |
} |
|
3458 |
||
3459 |
if (cur == Self) { |
|
3460 |
// TODO-FIXME: check for integer overflow! BUGID 6557169. |
|
3461 |
_recursions ++ ; |
|
3462 |
return ; |
|
3463 |
} |
|
3464 |
||
3465 |
if (Self->is_lock_owned ((address)cur)) { |
|
3466 |
assert (_recursions == 0, "internal state error"); |
|
3467 |
_recursions = 1 ; |
|
3468 |
// Commute owner from a thread-specific on-stack BasicLockObject address to |
|
3469 |
// a full-fledged "Thread *". |
|
3470 |
_owner = Self ; |
|
3471 |
OwnerIsThread = 1 ; |
|
3472 |
return ; |
|
3473 |
} |
|
3474 |
||
3475 |
// We've encountered genuine contention. |
|
3476 |
assert (Self->_Stalled == 0, "invariant") ; |
|
3477 |
Self->_Stalled = intptr_t(this) ; |
|
3478 |
||
3479 |
// Try one round of spinning *before* enqueueing Self |
|
3480 |
// and before going through the awkward and expensive state |
|
3481 |
// transitions. The following spin is strictly optional ... |
|
3482 |
// Note that if we acquire the monitor from an initial spin |
|
3483 |
// we forgo posting JVMTI events and firing DTRACE probes. |
|
3484 |
if (Knob_SpinEarly && TrySpin (Self) > 0) { |
|
3485 |
assert (_owner == Self , "invariant") ; |
|
3486 |
assert (_recursions == 0 , "invariant") ; |
|
3487 |
assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ; |
|
3488 |
Self->_Stalled = 0 ; |
|
3489 |
return ; |
|
3490 |
} |
|
3491 |
||
3492 |
assert (_owner != Self , "invariant") ; |
|
3493 |
assert (_succ != Self , "invariant") ; |
|
3494 |
assert (Self->is_Java_thread() , "invariant") ; |
|
3495 |
JavaThread * jt = (JavaThread *) Self ; |
|
3496 |
assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ; |
|
3497 |
assert (jt->thread_state() != _thread_blocked , "invariant") ; |
|
3498 |
assert (this->object() != NULL , "invariant") ; |
|
3499 |
assert (_count >= 0, "invariant") ; |
|
3500 |
||
3501 |
// Prevent deflation at STW-time. See deflate_idle_monitors() and is_busy(). |
|
3502 |
// Ensure the object-monitor relationship remains stable while there's contention. |
|
3503 |
Atomic::inc_ptr(&_count); |
|
3504 |
||
3505 |
{ // Change java thread status to indicate blocked on monitor enter. |
|
3506 |
JavaThreadBlockedOnMonitorEnterState jtbmes(jt, this); |
|
3507 |
||
3508 |
DTRACE_MONITOR_PROBE(contended__enter, this, object(), jt); |
|
3509 |
if (JvmtiExport::should_post_monitor_contended_enter()) { |
|
3510 |
JvmtiExport::post_monitor_contended_enter(jt, this); |
|
3511 |
} |
|
3512 |
||
3513 |
OSThreadContendState osts(Self->osthread()); |
|
3514 |
ThreadBlockInVM tbivm(jt); |
|
3515 |
||
3516 |
Self->set_current_pending_monitor(this); |
|
3517 |
||
3518 |
// TODO-FIXME: change the following for(;;) loop to straight-line code. |
|
3519 |
for (;;) { |
|
3520 |
jt->set_suspend_equivalent(); |
|
3521 |
// cleared by handle_special_suspend_equivalent_condition() |
|
3522 |
// or java_suspend_self() |
|
3523 |
||
3524 |
EnterI (THREAD) ; |
|
3525 |
||
3526 |
if (!ExitSuspendEquivalent(jt)) break ; |
|
3527 |
||
3528 |
// |
|
3529 |
// We have acquired the contended monitor, but while we were |
|
3530 |
// waiting another thread suspended us. We don't want to enter |
|
3531 |
// the monitor while suspended because that would surprise the |
|
3532 |
// thread that suspended us. |
|
3533 |
// |
|
3534 |
_recursions = 0 ; |
|
3535 |
_succ = NULL ; |
|
3536 |
exit (Self) ; |
|
3537 |
||
3538 |
jt->java_suspend_self(); |
|
3539 |
} |
|
3540 |
Self->set_current_pending_monitor(NULL); |
|
3541 |
} |
|
3542 |
||
3543 |
Atomic::dec_ptr(&_count); |
|
3544 |
assert (_count >= 0, "invariant") ; |
|
3545 |
Self->_Stalled = 0 ; |
|
3546 |
||
3547 |
// Must either set _recursions = 0 or ASSERT _recursions == 0. |
|
3548 |
assert (_recursions == 0 , "invariant") ; |
|
3549 |
assert (_owner == Self , "invariant") ; |
|
3550 |
assert (_succ != Self , "invariant") ; |
|
3551 |
assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ; |
|
3552 |
||
3553 |
// The thread -- now the owner -- is back in vm mode. |
|
3554 |
// Report the glorious news via TI,DTrace and jvmstat. |
|
3555 |
// The probe effect is non-trivial. All the reportage occurs |
|
3556 |
// while we hold the monitor, increasing the length of the critical |
|
3557 |
// section. Amdahl's parallel speedup law comes vividly into play. |
|
3558 |
// |
|
3559 |
// Another option might be to aggregate the events (thread local or |
|
3560 |
// per-monitor aggregation) and defer reporting until a more opportune |
|
3561 |
// time -- such as next time some thread encounters contention but has |
|
3562 |
// yet to acquire the lock. While spinning that thread could |
|
3563 |
// spinning we could increment JVMStat counters, etc. |
|
3564 |
||
3565 |
DTRACE_MONITOR_PROBE(contended__entered, this, object(), jt); |
|
3566 |
if (JvmtiExport::should_post_monitor_contended_entered()) { |
|
3567 |
JvmtiExport::post_monitor_contended_entered(jt, this); |
|
3568 |
} |
|
3569 |
if (ObjectSynchronizer::_sync_ContendedLockAttempts != NULL) { |
|
3570 |
ObjectSynchronizer::_sync_ContendedLockAttempts->inc() ; |
|
3571 |
} |
|
3572 |
} |
|
3573 |
||
3574 |
void ObjectMonitor::ExitEpilog (Thread * Self, ObjectWaiter * Wakee) { |
|
3575 |
assert (_owner == Self, "invariant") ; |
|
3576 |
||
3577 |
// Exit protocol: |
|
3578 |
// 1. ST _succ = wakee |
|
3579 |
// 2. membar #loadstore|#storestore; |
|
3580 |
// 2. ST _owner = NULL |
|
3581 |
// 3. unpark(wakee) |
|
3582 |
||
3583 |
_succ = Knob_SuccEnabled ? Wakee->_thread : NULL ; |
|
3584 |
ParkEvent * Trigger = Wakee->_event ; |
|
3585 |
||
3586 |
// Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again. |
|
3587 |
// The thread associated with Wakee may have grabbed the lock and "Wakee" may be |
|
3588 |
// out-of-scope (non-extant). |
|
3589 |
Wakee = NULL ; |
|
3590 |
||
3591 |
// Drop the lock |
|
3592 |
OrderAccess::release_store_ptr (&_owner, NULL) ; |
|
3593 |
OrderAccess::fence() ; // ST _owner vs LD in unpark() |
|
3594 |
||
3595 |
// TODO-FIXME: |
|
3596 |
// If there's a safepoint pending the best policy would be to |
|
3597 |
// get _this thread to a safepoint and only wake the successor |
|
3598 |
// after the safepoint completed. monitorexit uses a "leaf" |
|
3599 |
// state transition, however, so this thread can't become |
|
3600 |
// safe at this point in time. (Its stack isn't walkable). |
|
3601 |
// The next best thing is to defer waking the successor by |
|
3602 |
// adding to a list of thread to be unparked after at the |
|
3603 |
// end of the forthcoming STW). |
|
3604 |
if (SafepointSynchronize::do_call_back()) { |
|
3605 |
TEVENT (unpark before SAFEPOINT) ; |
|
3606 |
} |
|
3607 |
||
3608 |
// Possible optimizations ... |
|
3609 |
// |
|
3610 |
// * Consider: set Wakee->UnparkTime = timeNow() |
|
3611 |
// When the thread wakes up it'll compute (timeNow() - Self->UnparkTime()). |
|
3612 |
// By measuring recent ONPROC latency we can approximate the |
|
3613 |
// system load. In turn, we can feed that information back |
|
3614 |
// into the spinning & succession policies. |
|
3615 |
// (ONPROC latency correlates strongly with load). |
|
3616 |
// |
|
3617 |
// * Pull affinity: |
|
3618 |
// If the wakee is cold then transiently setting it's affinity |
|
3619 |
// to the current CPU is a good idea. |
|
3620 |
// See http://j2se.east/~dice/PERSIST/050624-PullAffinity.txt |
|
1665
7b9a44b26afd
6639341: sometimes contended-exit event comes after contended-entered on another thread
blacklion
parents:
1
diff
changeset
|
3621 |
DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self); |
1 | 3622 |
Trigger->unpark() ; |
3623 |
||
3624 |
// Maintain stats and report events to JVMTI |
|
3625 |
if (ObjectSynchronizer::_sync_Parks != NULL) { |
|
3626 |
ObjectSynchronizer::_sync_Parks->inc() ; |
|
3627 |
} |
|
3628 |
} |
|
3629 |
||
3630 |
||
3631 |
// exit() |
|
3632 |
// ~~~~~~ |
|
3633 |
// Note that the collector can't reclaim the objectMonitor or deflate |
|
3634 |
// the object out from underneath the thread calling ::exit() as the |
|
3635 |
// thread calling ::exit() never transitions to a stable state. |
|
3636 |
// This inhibits GC, which in turn inhibits asynchronous (and |
|
3637 |
// inopportune) reclamation of "this". |
|
3638 |
// |
|
3639 |
// We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ; |
|
3640 |
// There's one exception to the claim above, however. EnterI() can call |
|
3641 |
// exit() to drop a lock if the acquirer has been externally suspended. |
|
3642 |
// In that case exit() is called with _thread_state as _thread_blocked, |
|
3643 |
// but the monitor's _count field is > 0, which inhibits reclamation. |
|
3644 |
// |
|
3645 |
// 1-0 exit |
|
3646 |
// ~~~~~~~~ |
|
3647 |
// ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of |
|
3648 |
// the fast-path operators have been optimized so the common ::exit() |
|
3649 |
// operation is 1-0. See i486.ad fast_unlock(), for instance. |
|
3650 |
// The code emitted by fast_unlock() elides the usual MEMBAR. This |
|
3651 |
// greatly improves latency -- MEMBAR and CAS having considerable local |
|
3652 |
// latency on modern processors -- but at the cost of "stranding". Absent the |
|
3653 |
// MEMBAR, a thread in fast_unlock() can race a thread in the slow |
|
3654 |
// ::enter() path, resulting in the entering thread being stranding |
|
3655 |
// and a progress-liveness failure. Stranding is extremely rare. |
|
3656 |
// We use timers (timed park operations) & periodic polling to detect |
|
3657 |
// and recover from stranding. Potentially stranded threads periodically |
|
3658 |
// wake up and poll the lock. See the usage of the _Responsible variable. |
|
3659 |
// |
|
3660 |
// The CAS() in enter provides for safety and exclusion, while the CAS or |
|
3661 |
// MEMBAR in exit provides for progress and avoids stranding. 1-0 locking |
|
3662 |
// eliminates the CAS/MEMBAR from the exist path, but it admits stranding. |
|
3663 |
// We detect and recover from stranding with timers. |
|
3664 |
// |
|
3665 |
// If a thread transiently strands it'll park until (a) another |
|
3666 |
// thread acquires the lock and then drops the lock, at which time the |
|
3667 |
// exiting thread will notice and unpark the stranded thread, or, (b) |
|
3668 |
// the timer expires. If the lock is high traffic then the stranding latency |
|
3669 |
// will be low due to (a). If the lock is low traffic then the odds of |
|
3670 |
// stranding are lower, although the worst-case stranding latency |
|
3671 |
// is longer. Critically, we don't want to put excessive load in the |
|
3672 |
// platform's timer subsystem. We want to minimize both the timer injection |
|
3673 |
// rate (timers created/sec) as well as the number of timers active at |
|
3674 |
// any one time. (more precisely, we want to minimize timer-seconds, which is |
|
3675 |
// the integral of the # of active timers at any instant over time). |
|
3676 |
// Both impinge on OS scalability. Given that, at most one thread parked on |
|
3677 |
// a monitor will use a timer. |
|
3678 |
||
3679 |
void ATTR ObjectMonitor::exit(TRAPS) { |
|
3680 |
Thread * Self = THREAD ; |
|
3681 |
if (THREAD != _owner) { |
|
3682 |
if (THREAD->is_lock_owned((address) _owner)) { |
|
3683 |
// Transmute _owner from a BasicLock pointer to a Thread address. |
|
3684 |
// We don't need to hold _mutex for this transition. |
|
3685 |
// Non-null to Non-null is safe as long as all readers can |
|
3686 |
// tolerate either flavor. |
|
3687 |
assert (_recursions == 0, "invariant") ; |
|
3688 |
_owner = THREAD ; |
|
3689 |
_recursions = 0 ; |
|
3690 |
OwnerIsThread = 1 ; |
|
3691 |
} else { |
|
3692 |
// NOTE: we need to handle unbalanced monitor enter/exit |
|
3693 |
// in native code by throwing an exception. |
|
3694 |
// TODO: Throw an IllegalMonitorStateException ? |
|
3695 |
TEVENT (Exit - Throw IMSX) ; |
|
3696 |
assert(false, "Non-balanced monitor enter/exit!"); |
|
3697 |
if (false) { |
|
3698 |
THROW(vmSymbols::java_lang_IllegalMonitorStateException()); |
|
3699 |
} |
|
3700 |
return; |
|
3701 |
} |
|
3702 |
} |
|
3703 |
||
3704 |
if (_recursions != 0) { |
|
3705 |
_recursions--; // this is simple recursive enter |
|
3706 |
TEVENT (Inflated exit - recursive) ; |
|
3707 |
return ; |
|
3708 |
} |
|
3709 |
||
3710 |
// Invariant: after setting Responsible=null an thread must execute |
|
3711 |
// a MEMBAR or other serializing instruction before fetching EntryList|cxq. |
|
3712 |
if ((SyncFlags & 4) == 0) { |
|
3713 |
_Responsible = NULL ; |
|
3714 |
} |
|
3715 |
||
3716 |
for (;;) { |
|
3717 |
assert (THREAD == _owner, "invariant") ; |
|
3718 |
||
3719 |
// Fast-path monitor exit: |
|
3720 |
// |
|
3721 |
// Observe the Dekker/Lamport duality: |
|
3722 |
// A thread in ::exit() executes: |
|
3723 |
// ST Owner=null; MEMBAR; LD EntryList|cxq. |
|
3724 |
// A thread in the contended ::enter() path executes the complementary: |
|
3725 |
// ST EntryList|cxq = nonnull; MEMBAR; LD Owner. |
|
3726 |
// |
|
3727 |
// Note that there's a benign race in the exit path. We can drop the |
|
3728 |
// lock, another thread can reacquire the lock immediately, and we can |
|
3729 |
// then wake a thread unnecessarily (yet another flavor of futile wakeup). |
|
3730 |
// This is benign, and we've structured the code so the windows are short |
|
3731 |
// and the frequency of such futile wakeups is low. |
|
3732 |
// |
|
3733 |
// We could eliminate the race by encoding both the "LOCKED" state and |
|
3734 |
// the queue head in a single word. Exit would then use either CAS to |
|
3735 |
// clear the LOCKED bit/byte. This precludes the desirable 1-0 optimization, |
|
3736 |
// however. |
|
3737 |
// |
|
3738 |
// Possible fast-path ::exit() optimization: |
|
3739 |
// The current fast-path exit implementation fetches both cxq and EntryList. |
|
3740 |
// See also i486.ad fast_unlock(). Testing has shown that two LDs |
|
3741 |
// isn't measurably slower than a single LD on any platforms. |
|
3742 |
// Still, we could reduce the 2 LDs to one or zero by one of the following: |
|
3743 |
// |
|
3744 |
// - Use _count instead of cxq|EntryList |
|
3745 |
// We intend to eliminate _count, however, when we switch |
|
3746 |
// to on-the-fly deflation in ::exit() as is used in |
|
3747 |
// Metalocks and RelaxedLocks. |
|
3748 |
// |
|
3749 |
// - Establish the invariant that cxq == null implies EntryList == null. |
|
3750 |
// set cxq == EMPTY (1) to encode the state where cxq is empty |
|
3751 |
// by EntryList != null. EMPTY is a distinguished value. |
|
3752 |
// The fast-path exit() would fetch cxq but not EntryList. |
|
3753 |
// |
|
3754 |
// - Encode succ as follows: |
|
3755 |
// succ = t : Thread t is the successor -- t is ready or is spinning. |
|
3756 |
// Exiting thread does not need to wake a successor. |
|
3757 |
// succ = 0 : No successor required -> (EntryList|cxq) == null |
|
3758 |
// Exiting thread does not need to wake a successor |
|
3759 |
// succ = 1 : Successor required -> (EntryList|cxq) != null and |
|
3760 |
// logically succ == null. |
|
3761 |
// Exiting thread must wake a successor. |
|
3762 |
// |
|
3763 |
// The 1-1 fast-exit path would appear as : |
|
3764 |
// _owner = null ; membar ; |
|
3765 |
// if (_succ == 1 && CAS (&_owner, null, Self) == null) goto SlowPath |
|
3766 |
// goto FastPathDone ; |
|
3767 |
// |
|
3768 |
// and the 1-0 fast-exit path would appear as: |
|
3769 |
// if (_succ == 1) goto SlowPath |
|
3770 |
// Owner = null ; |
|
3771 |
// goto FastPathDone |
|
3772 |
// |
|
3773 |
// - Encode the LSB of _owner as 1 to indicate that exit() |
|
3774 |
// must use the slow-path and make a successor ready. |
|
3775 |
// (_owner & 1) == 0 IFF succ != null || (EntryList|cxq) == null |
|
3776 |
// (_owner & 1) == 0 IFF succ == null && (EntryList|cxq) != null (obviously) |
|
3777 |
// The 1-0 fast exit path would read: |
|
3778 |
// if (_owner != Self) goto SlowPath |
|
3779 |
// _owner = null |
|
3780 |
// goto FastPathDone |
|
3781 |
||
3782 |
if (Knob_ExitPolicy == 0) { |
|
3783 |
// release semantics: prior loads and stores from within the critical section |
|
3784 |
// must not float (reorder) past the following store that drops the lock. |
|
3785 |
// On SPARC that requires MEMBAR #loadstore|#storestore. |
|
3786 |
// But of course in TSO #loadstore|#storestore is not required. |
|
3787 |
// I'd like to write one of the following: |
|
3788 |
// A. OrderAccess::release() ; _owner = NULL |
|
3789 |
// B. OrderAccess::loadstore(); OrderAccess::storestore(); _owner = NULL; |
|
3790 |
// Unfortunately OrderAccess::release() and OrderAccess::loadstore() both |
|
3791 |
// store into a _dummy variable. That store is not needed, but can result |
|
3792 |
// in massive wasteful coherency traffic on classic SMP systems. |
|
3793 |
// Instead, I use release_store(), which is implemented as just a simple |
|
3794 |
// ST on x64, x86 and SPARC. |
|
3795 |
OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock |
|
3796 |
OrderAccess::storeload() ; // See if we need to wake a successor |
|
3797 |
if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) { |
|
3798 |
TEVENT (Inflated exit - simple egress) ; |
|
3799 |
return ; |
|
3800 |
} |
|
3801 |
TEVENT (Inflated exit - complex egress) ; |
|
3802 |
||
3803 |
// Normally the exiting thread is responsible for ensuring succession, |
|
3804 |
// but if other successors are ready or other entering threads are spinning |
|
3805 |
// then this thread can simply store NULL into _owner and exit without |
|
3806 |
// waking a successor. The existence of spinners or ready successors |
|
3807 |
// guarantees proper succession (liveness). Responsibility passes to the |
|
3808 |
// ready or running successors. The exiting thread delegates the duty. |
|
3809 |
// More precisely, if a successor already exists this thread is absolved |
|
3810 |
// of the responsibility of waking (unparking) one. |
|
3811 |
// |
|
3812 |
// The _succ variable is critical to reducing futile wakeup frequency. |
|
3813 |
// _succ identifies the "heir presumptive" thread that has been made |
|
3814 |
// ready (unparked) but that has not yet run. We need only one such |
|
3815 |
// successor thread to guarantee progress. |
|
3816 |
// See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf |
|
3817 |
// section 3.3 "Futile Wakeup Throttling" for details. |
|
3818 |
// |
|
3819 |
// Note that spinners in Enter() also set _succ non-null. |
|
3820 |
// In the current implementation spinners opportunistically set |
|
3821 |
// _succ so that exiting threads might avoid waking a successor. |
|
3822 |
// Another less appealing alternative would be for the exiting thread |
|
3823 |
// to drop the lock and then spin briefly to see if a spinner managed |
|
3824 |
// to acquire the lock. If so, the exiting thread could exit |
|
3825 |
// immediately without waking a successor, otherwise the exiting |
|
3826 |
// thread would need to dequeue and wake a successor. |
|
3827 |
// (Note that we'd need to make the post-drop spin short, but no |
|
3828 |
// shorter than the worst-case round-trip cache-line migration time. |
|
3829 |
// The dropped lock needs to become visible to the spinner, and then |
|
3830 |
// the acquisition of the lock by the spinner must become visible to |
|
3831 |
// the exiting thread). |
|
3832 |
// |
|
3833 |
||
3834 |
// It appears that an heir-presumptive (successor) must be made ready. |
|
3835 |
// Only the current lock owner can manipulate the EntryList or |
|
3836 |
// drain _cxq, so we need to reacquire the lock. If we fail |
|
3837 |
// to reacquire the lock the responsibility for ensuring succession |
|
3838 |
// falls to the new owner. |
|
3839 |
// |
|
3840 |
if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) { |
|
3841 |
return ; |
|
3842 |
} |
|
3843 |
TEVENT (Exit - Reacquired) ; |
|
3844 |
} else { |
|
3845 |
if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) { |
|
3846 |
OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock |
|
3847 |
OrderAccess::storeload() ; |
|
3848 |
// Ratify the previously observed values. |
|
3849 |
if (_cxq == NULL || _succ != NULL) { |
|
3850 |
TEVENT (Inflated exit - simple egress) ; |
|
3851 |
return ; |
|
3852 |
} |
|
3853 |
||
3854 |
// inopportune interleaving -- the exiting thread (this thread) |
|
3855 |
// in the fast-exit path raced an entering thread in the slow-enter |
|
3856 |
// path. |
|
3857 |
// We have two choices: |
|
3858 |
// A. Try to reacquire the lock. |
|
3859 |
// If the CAS() fails return immediately, otherwise |
|
3860 |
// we either restart/rerun the exit operation, or simply |
|
3861 |
// fall-through into the code below which wakes a successor. |
|
3862 |
// B. If the elements forming the EntryList|cxq are TSM |
|
3863 |
// we could simply unpark() the lead thread and return |
|
3864 |
// without having set _succ. |
|
3865 |
if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) { |
|
3866 |
TEVENT (Inflated exit - reacquired succeeded) ; |
|
3867 |
return ; |
|
3868 |
} |
|
3869 |
TEVENT (Inflated exit - reacquired failed) ; |
|
3870 |
} else { |
|
3871 |
TEVENT (Inflated exit - complex egress) ; |
|
3872 |
} |
|
3873 |
} |
|
3874 |
||
3875 |
guarantee (_owner == THREAD, "invariant") ; |
|
3876 |
||
3877 |
// Select an appropriate successor ("heir presumptive") from the EntryList |
|
3878 |
// and make it ready. Generally we just wake the head of EntryList . |
|
3879 |
// There's no algorithmic constraint that we use the head - it's just |
|
3880 |
// a policy decision. Note that the thread at head of the EntryList |
|
3881 |
// remains at the head until it acquires the lock. This means we'll |
|
3882 |
// repeatedly wake the same thread until it manages to grab the lock. |
|
3883 |
// This is generally a good policy - if we're seeing lots of futile wakeups |
|
3884 |
// at least we're waking/rewaking a thread that's like to be hot or warm |
|
3885 |
// (have residual D$ and TLB affinity). |
|
3886 |
// |
|
3887 |
// "Wakeup locality" optimization: |
|
3888 |
// http://j2se.east/~dice/PERSIST/040825-WakeLocality.txt |
|
3889 |
// In the future we'll try to bias the selection mechanism |
|
3890 |
// to preferentially pick a thread that recently ran on |
|
3891 |
// a processor element that shares cache with the CPU on which |
|
3892 |
// the exiting thread is running. We need access to Solaris' |
|
3893 |
// schedctl.sc_cpu to make that work. |
|
3894 |
// |
|
3895 |
ObjectWaiter * w = NULL ; |
|
3896 |
int QMode = Knob_QMode ; |
|
3897 |
||
3898 |
if (QMode == 2 && _cxq != NULL) { |
|
3899 |
// QMode == 2 : cxq has precedence over EntryList. |
|
3900 |
// Try to directly wake a successor from the cxq. |
|
3901 |
// If successful, the successor will need to unlink itself from cxq. |
|
3902 |
w = _cxq ; |
|
3903 |
assert (w != NULL, "invariant") ; |
|
3904 |
assert (w->TState == ObjectWaiter::TS_CXQ, "Invariant") ; |
|
3905 |
ExitEpilog (Self, w) ; |
|
3906 |
return ; |
|
3907 |
} |
|
3908 |
||
3909 |
if (QMode == 3 && _cxq != NULL) { |
|
3910 |
// Aggressively drain cxq into EntryList at the first opportunity. |
|
3911 |
// This policy ensure that recently-run threads live at the head of EntryList. |
|
3912 |
// Drain _cxq into EntryList - bulk transfer. |
|
3913 |
// First, detach _cxq. |
|
3914 |
// The following loop is tantamount to: w = swap (&cxq, NULL) |
|
3915 |
w = _cxq ; |
|
3916 |
for (;;) { |
|
3917 |
assert (w != NULL, "Invariant") ; |
|
3918 |
ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; |
|
3919 |
if (u == w) break ; |
|
3920 |
w = u ; |
|
3921 |
} |
|
3922 |
assert (w != NULL , "invariant") ; |
|
3923 |
||
3924 |
ObjectWaiter * q = NULL ; |
|
3925 |
ObjectWaiter * p ; |
|
3926 |
for (p = w ; p != NULL ; p = p->_next) { |
|
3927 |
guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; |
|
3928 |
p->TState = ObjectWaiter::TS_ENTER ; |
|
3929 |
p->_prev = q ; |
|
3930 |
q = p ; |
|
3931 |
} |
|
3932 |
||
3933 |
// Append the RATs to the EntryList |
|
3934 |
// TODO: organize EntryList as a CDLL so we can locate the tail in constant-time. |
|
3935 |
ObjectWaiter * Tail ; |
|
3936 |
for (Tail = _EntryList ; Tail != NULL && Tail->_next != NULL ; Tail = Tail->_next) ; |
|
3937 |
if (Tail == NULL) { |
|
3938 |
_EntryList = w ; |
|
3939 |
} else { |
|
3940 |
Tail->_next = w ; |
|
3941 |
w->_prev = Tail ; |
|
3942 |
} |
|
3943 |
||
3944 |
// Fall thru into code that tries to wake a successor from EntryList |
|
3945 |
} |
|
3946 |
||
3947 |
if (QMode == 4 && _cxq != NULL) { |
|
3948 |
// Aggressively drain cxq into EntryList at the first opportunity. |
|
3949 |
// This policy ensure that recently-run threads live at the head of EntryList. |
|
3950 |
||
3951 |
// Drain _cxq into EntryList - bulk transfer. |
|
3952 |
// First, detach _cxq. |
|
3953 |
// The following loop is tantamount to: w = swap (&cxq, NULL) |
|
3954 |
w = _cxq ; |
|
3955 |
for (;;) { |
|
3956 |
assert (w != NULL, "Invariant") ; |
|
3957 |
ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; |
|
3958 |
if (u == w) break ; |
|
3959 |
w = u ; |
|
3960 |
} |
|
3961 |
assert (w != NULL , "invariant") ; |
|
3962 |
||
3963 |
ObjectWaiter * q = NULL ; |
|
3964 |
ObjectWaiter * p ; |
|
3965 |
for (p = w ; p != NULL ; p = p->_next) { |
|
3966 |
guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; |
|
3967 |
p->TState = ObjectWaiter::TS_ENTER ; |
|
3968 |
p->_prev = q ; |
|
3969 |
q = p ; |
|
3970 |
} |
|
3971 |
||
3972 |
// Prepend the RATs to the EntryList |
|
3973 |
if (_EntryList != NULL) { |
|
3974 |
q->_next = _EntryList ; |
|
3975 |
_EntryList->_prev = q ; |
|
3976 |
} |
|
3977 |
_EntryList = w ; |
|
3978 |
||
3979 |
// Fall thru into code that tries to wake a successor from EntryList |
|
3980 |
} |
|
3981 |
||
3982 |
w = _EntryList ; |
|
3983 |
if (w != NULL) { |
|
3984 |
// I'd like to write: guarantee (w->_thread != Self). |
|
3985 |
// But in practice an exiting thread may find itself on the EntryList. |
|
3986 |
// Lets say thread T1 calls O.wait(). Wait() enqueues T1 on O's waitset and |
|
3987 |
// then calls exit(). Exit release the lock by setting O._owner to NULL. |
|
3988 |
// Lets say T1 then stalls. T2 acquires O and calls O.notify(). The |
|
3989 |
// notify() operation moves T1 from O's waitset to O's EntryList. T2 then |
|
3990 |
// release the lock "O". T2 resumes immediately after the ST of null into |
|
3991 |
// _owner, above. T2 notices that the EntryList is populated, so it |
|
3992 |
// reacquires the lock and then finds itself on the EntryList. |
|
3993 |
// Given all that, we have to tolerate the circumstance where "w" is |
|
3994 |
// associated with Self. |
|
3995 |
assert (w->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
3996 |
ExitEpilog (Self, w) ; |
|
3997 |
return ; |
|
3998 |
} |
|
3999 |
||
4000 |
// If we find that both _cxq and EntryList are null then just |
|
4001 |
// re-run the exit protocol from the top. |
|
4002 |
w = _cxq ; |
|
4003 |
if (w == NULL) continue ; |
|
4004 |
||
4005 |
// Drain _cxq into EntryList - bulk transfer. |
|
4006 |
// First, detach _cxq. |
|
4007 |
// The following loop is tantamount to: w = swap (&cxq, NULL) |
|
4008 |
for (;;) { |
|
4009 |
assert (w != NULL, "Invariant") ; |
|
4010 |
ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; |
|
4011 |
if (u == w) break ; |
|
4012 |
w = u ; |
|
4013 |
} |
|
4014 |
TEVENT (Inflated exit - drain cxq into EntryList) ; |
|
4015 |
||
4016 |
assert (w != NULL , "invariant") ; |
|
4017 |
assert (_EntryList == NULL , "invariant") ; |
|
4018 |
||
4019 |
// Convert the LIFO SLL anchored by _cxq into a DLL. |
|
4020 |
// The list reorganization step operates in O(LENGTH(w)) time. |
|
4021 |
// It's critical that this step operate quickly as |
|
4022 |
// "Self" still holds the outer-lock, restricting parallelism |
|
4023 |
// and effectively lengthening the critical section. |
|
4024 |
// Invariant: s chases t chases u. |
|
4025 |
// TODO-FIXME: consider changing EntryList from a DLL to a CDLL so |
|
4026 |
// we have faster access to the tail. |
|
4027 |
||
4028 |
if (QMode == 1) { |
|
4029 |
// QMode == 1 : drain cxq to EntryList, reversing order |
|
4030 |
// We also reverse the order of the list. |
|
4031 |
ObjectWaiter * s = NULL ; |
|
4032 |
ObjectWaiter * t = w ; |
|
4033 |
ObjectWaiter * u = NULL ; |
|
4034 |
while (t != NULL) { |
|
4035 |
guarantee (t->TState == ObjectWaiter::TS_CXQ, "invariant") ; |
|
4036 |
t->TState = ObjectWaiter::TS_ENTER ; |
|
4037 |
u = t->_next ; |
|
4038 |
t->_prev = u ; |
|
4039 |
t->_next = s ; |
|
4040 |
s = t; |
|
4041 |
t = u ; |
|
4042 |
} |
|
4043 |
_EntryList = s ; |
|
4044 |
assert (s != NULL, "invariant") ; |
|
4045 |
} else { |
|
4046 |
// QMode == 0 or QMode == 2 |
|
4047 |
_EntryList = w ; |
|
4048 |
ObjectWaiter * q = NULL ; |
|
4049 |
ObjectWaiter * p ; |
|
4050 |
for (p = w ; p != NULL ; p = p->_next) { |
|
4051 |
guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; |
|
4052 |
p->TState = ObjectWaiter::TS_ENTER ; |
|
4053 |
p->_prev = q ; |
|
4054 |
q = p ; |
|
4055 |
} |
|
4056 |
} |
|
4057 |
||
4058 |
// In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = NULL |
|
4059 |
// The MEMBAR is satisfied by the release_store() operation in ExitEpilog(). |
|
4060 |
||
4061 |
// See if we can abdicate to a spinner instead of waking a thread. |
|
4062 |
// A primary goal of the implementation is to reduce the |
|
4063 |
// context-switch rate. |
|
4064 |
if (_succ != NULL) continue; |
|
4065 |
||
4066 |
w = _EntryList ; |
|
4067 |
if (w != NULL) { |
|
4068 |
guarantee (w->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
4069 |
ExitEpilog (Self, w) ; |
|
4070 |
return ; |
|
4071 |
} |
|
4072 |
} |
|
4073 |
} |
|
4074 |
// complete_exit exits a lock returning recursion count |
|
4075 |
// complete_exit/reenter operate as a wait without waiting |
|
4076 |
// complete_exit requires an inflated monitor |
|
4077 |
// The _owner field is not always the Thread addr even with an |
|
4078 |
// inflated monitor, e.g. the monitor can be inflated by a non-owning |
|
4079 |
// thread due to contention. |
|
4080 |
intptr_t ObjectMonitor::complete_exit(TRAPS) { |
|
4081 |
Thread * const Self = THREAD; |
|
4082 |
assert(Self->is_Java_thread(), "Must be Java thread!"); |
|
4083 |
JavaThread *jt = (JavaThread *)THREAD; |
|
4084 |
||
4085 |
DeferredInitialize(); |
|
4086 |
||
4087 |
if (THREAD != _owner) { |
|
4088 |
if (THREAD->is_lock_owned ((address)_owner)) { |
|
4089 |
assert(_recursions == 0, "internal state error"); |
|
4090 |
_owner = THREAD ; /* Convert from basiclock addr to Thread addr */ |
|
4091 |
_recursions = 0 ; |
|
4092 |
OwnerIsThread = 1 ; |
|
4093 |
} |
|
4094 |
} |
|
4095 |
||
4096 |
guarantee(Self == _owner, "complete_exit not owner"); |
|
4097 |
intptr_t save = _recursions; // record the old recursion count |
|
4098 |
_recursions = 0; // set the recursion level to be 0 |
|
4099 |
exit (Self) ; // exit the monitor |
|
4100 |
guarantee (_owner != Self, "invariant"); |
|
4101 |
return save; |
|
4102 |
} |
|
4103 |
||
4104 |
// reenter() enters a lock and sets recursion count |
|
4105 |
// complete_exit/reenter operate as a wait without waiting |
|
4106 |
void ObjectMonitor::reenter(intptr_t recursions, TRAPS) { |
|
4107 |
Thread * const Self = THREAD; |
|
4108 |
assert(Self->is_Java_thread(), "Must be Java thread!"); |
|
4109 |
JavaThread *jt = (JavaThread *)THREAD; |
|
4110 |
||
4111 |
guarantee(_owner != Self, "reenter already owner"); |
|
4112 |
enter (THREAD); // enter the monitor |
|
4113 |
guarantee (_recursions == 0, "reenter recursion"); |
|
4114 |
_recursions = recursions; |
|
4115 |
return; |
|
4116 |
} |
|
4117 |
||
4118 |
// Note: a subset of changes to ObjectMonitor::wait() |
|
4119 |
// will need to be replicated in complete_exit above |
|
4120 |
void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) { |
|
4121 |
Thread * const Self = THREAD ; |
|
4122 |
assert(Self->is_Java_thread(), "Must be Java thread!"); |
|
4123 |
JavaThread *jt = (JavaThread *)THREAD; |
|
4124 |
||
4125 |
DeferredInitialize () ; |
|
4126 |
||
4127 |
// Throw IMSX or IEX. |
|
4128 |
CHECK_OWNER(); |
|
4129 |
||
4130 |
// check for a pending interrupt |
|
4131 |
if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) { |
|
4132 |
// post monitor waited event. Note that this is past-tense, we are done waiting. |
|
4133 |
if (JvmtiExport::should_post_monitor_waited()) { |
|
4134 |
// Note: 'false' parameter is passed here because the |
|
4135 |
// wait was not timed out due to thread interrupt. |
|
4136 |
JvmtiExport::post_monitor_waited(jt, this, false); |
|
4137 |
} |
|
4138 |
TEVENT (Wait - Throw IEX) ; |
|
4139 |
THROW(vmSymbols::java_lang_InterruptedException()); |
|
4140 |
return ; |
|
4141 |
} |
|
4142 |
TEVENT (Wait) ; |
|
4143 |
||
4144 |
assert (Self->_Stalled == 0, "invariant") ; |
|
4145 |
Self->_Stalled = intptr_t(this) ; |
|
4146 |
jt->set_current_waiting_monitor(this); |
|
4147 |
||
4148 |
// create a node to be put into the queue |
|
4149 |
// Critically, after we reset() the event but prior to park(), we must check |
|
4150 |
// for a pending interrupt. |
|
4151 |
ObjectWaiter node(Self); |
|
4152 |
node.TState = ObjectWaiter::TS_WAIT ; |
|
4153 |
Self->_ParkEvent->reset() ; |
|
4154 |
OrderAccess::fence(); // ST into Event; membar ; LD interrupted-flag |
|
4155 |
||
4156 |
// Enter the waiting queue, which is a circular doubly linked list in this case |
|
4157 |
// but it could be a priority queue or any data structure. |
|
4158 |
// _WaitSetLock protects the wait queue. Normally the wait queue is accessed only |
|
4159 |
// by the the owner of the monitor *except* in the case where park() |
|
4160 |
// returns because of a timeout of interrupt. Contention is exceptionally rare |
|
4161 |
// so we use a simple spin-lock instead of a heavier-weight blocking lock. |
|
4162 |
||
4163 |
Thread::SpinAcquire (&_WaitSetLock, "WaitSet - add") ; |
|
4164 |
AddWaiter (&node) ; |
|
4165 |
Thread::SpinRelease (&_WaitSetLock) ; |
|
4166 |
||
4167 |
if ((SyncFlags & 4) == 0) { |
|
4168 |
_Responsible = NULL ; |
|
4169 |
} |
|
4170 |
intptr_t save = _recursions; // record the old recursion count |
|
4171 |
_waiters++; // increment the number of waiters |
|
4172 |
_recursions = 0; // set the recursion level to be 1 |
|
4173 |
exit (Self) ; // exit the monitor |
|
4174 |
guarantee (_owner != Self, "invariant") ; |
|
4175 |
||
4176 |
// As soon as the ObjectMonitor's ownership is dropped in the exit() |
|
4177 |
// call above, another thread can enter() the ObjectMonitor, do the |
|
4178 |
// notify(), and exit() the ObjectMonitor. If the other thread's |
|
4179 |
// exit() call chooses this thread as the successor and the unpark() |
|
4180 |
// call happens to occur while this thread is posting a |
|
4181 |
// MONITOR_CONTENDED_EXIT event, then we run the risk of the event |
|
4182 |
// handler using RawMonitors and consuming the unpark(). |
|
4183 |
// |
|
4184 |
// To avoid the problem, we re-post the event. This does no harm |
|
4185 |
// even if the original unpark() was not consumed because we are the |
|
4186 |
// chosen successor for this monitor. |
|
4187 |
if (node._notified != 0 && _succ == Self) { |
|
4188 |
node._event->unpark(); |
|
4189 |
} |
|
4190 |
||
4191 |
// The thread is on the WaitSet list - now park() it. |
|
4192 |
// On MP systems it's conceivable that a brief spin before we park |
|
4193 |
// could be profitable. |
|
4194 |
// |
|
4195 |
// TODO-FIXME: change the following logic to a loop of the form |
|
4196 |
// while (!timeout && !interrupted && _notified == 0) park() |
|
4197 |
||
4198 |
int ret = OS_OK ; |
|
4199 |
int WasNotified = 0 ; |
|
4200 |
{ // State transition wrappers |
|
4201 |
OSThread* osthread = Self->osthread(); |
|
4202 |
OSThreadWaitState osts(osthread, true); |
|
4203 |
{ |
|
4204 |
ThreadBlockInVM tbivm(jt); |
|
4205 |
// Thread is in thread_blocked state and oop access is unsafe. |
|
4206 |
jt->set_suspend_equivalent(); |
|
4207 |
||
4208 |
if (interruptible && (Thread::is_interrupted(THREAD, false) || HAS_PENDING_EXCEPTION)) { |
|
4209 |
// Intentionally empty |
|
4210 |
} else |
|
4211 |
if (node._notified == 0) { |
|
4212 |
if (millis <= 0) { |
|
4213 |
Self->_ParkEvent->park () ; |
|
4214 |
} else { |
|
4215 |
ret = Self->_ParkEvent->park (millis) ; |
|
4216 |
} |
|
4217 |
} |
|
4218 |
||
4219 |
// were we externally suspended while we were waiting? |
|
4220 |
if (ExitSuspendEquivalent (jt)) { |
|
4221 |
// TODO-FIXME: add -- if succ == Self then succ = null. |
|
4222 |
jt->java_suspend_self(); |
|
4223 |
} |
|
4224 |
||
4225 |
} // Exit thread safepoint: transition _thread_blocked -> _thread_in_vm |
|
4226 |
||
4227 |
||
4228 |
// Node may be on the WaitSet, the EntryList (or cxq), or in transition |
|
4229 |
// from the WaitSet to the EntryList. |
|
4230 |
// See if we need to remove Node from the WaitSet. |
|
4231 |
// We use double-checked locking to avoid grabbing _WaitSetLock |
|
4232 |
// if the thread is not on the wait queue. |
|
4233 |
// |
|
4234 |
// Note that we don't need a fence before the fetch of TState. |
|
4235 |
// In the worst case we'll fetch a old-stale value of TS_WAIT previously |
|
4236 |
// written by the is thread. (perhaps the fetch might even be satisfied |
|
4237 |
// by a look-aside into the processor's own store buffer, although given |
|
4238 |
// the length of the code path between the prior ST and this load that's |
|
4239 |
// highly unlikely). If the following LD fetches a stale TS_WAIT value |
|
4240 |
// then we'll acquire the lock and then re-fetch a fresh TState value. |
|
4241 |
// That is, we fail toward safety. |
|
4242 |
||
4243 |
if (node.TState == ObjectWaiter::TS_WAIT) { |
|
4244 |
Thread::SpinAcquire (&_WaitSetLock, "WaitSet - unlink") ; |
|
4245 |
if (node.TState == ObjectWaiter::TS_WAIT) { |
|
4246 |
DequeueSpecificWaiter (&node) ; // unlink from WaitSet |
|
4247 |
assert(node._notified == 0, "invariant"); |
|
4248 |
node.TState = ObjectWaiter::TS_RUN ; |
|
4249 |
} |
|
4250 |
Thread::SpinRelease (&_WaitSetLock) ; |
|
4251 |
} |
|
4252 |
||
4253 |
// The thread is now either on off-list (TS_RUN), |
|
4254 |
// on the EntryList (TS_ENTER), or on the cxq (TS_CXQ). |
|
4255 |
// The Node's TState variable is stable from the perspective of this thread. |
|
4256 |
// No other threads will asynchronously modify TState. |
|
4257 |
guarantee (node.TState != ObjectWaiter::TS_WAIT, "invariant") ; |
|
4258 |
OrderAccess::loadload() ; |
|
4259 |
if (_succ == Self) _succ = NULL ; |
|
4260 |
WasNotified = node._notified ; |
|
4261 |
||
4262 |
// Reentry phase -- reacquire the monitor. |
|
4263 |
// re-enter contended monitor after object.wait(). |
|
4264 |
// retain OBJECT_WAIT state until re-enter successfully completes |
|
4265 |
// Thread state is thread_in_vm and oop access is again safe, |
|
4266 |
// although the raw address of the object may have changed. |
|
4267 |
// (Don't cache naked oops over safepoints, of course). |
|
4268 |
||
4269 |
// post monitor waited event. Note that this is past-tense, we are done waiting. |
|
4270 |
if (JvmtiExport::should_post_monitor_waited()) { |
|
4271 |
JvmtiExport::post_monitor_waited(jt, this, ret == OS_TIMEOUT); |
|
4272 |
} |
|
4273 |
OrderAccess::fence() ; |
|
4274 |
||
4275 |
assert (Self->_Stalled != 0, "invariant") ; |
|
4276 |
Self->_Stalled = 0 ; |
|
4277 |
||
4278 |
assert (_owner != Self, "invariant") ; |
|
4279 |
ObjectWaiter::TStates v = node.TState ; |
|
4280 |
if (v == ObjectWaiter::TS_RUN) { |
|
4281 |
enter (Self) ; |
|
4282 |
} else { |
|
4283 |
guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ; |
|
4284 |
ReenterI (Self, &node) ; |
|
4285 |
node.wait_reenter_end(this); |
|
4286 |
} |
|
4287 |
||
4288 |
// Self has reacquired the lock. |
|
4289 |
// Lifecycle - the node representing Self must not appear on any queues. |
|
4290 |
// Node is about to go out-of-scope, but even if it were immortal we wouldn't |
|
4291 |
// want residual elements associated with this thread left on any lists. |
|
4292 |
guarantee (node.TState == ObjectWaiter::TS_RUN, "invariant") ; |
|
4293 |
assert (_owner == Self, "invariant") ; |
|
4294 |
assert (_succ != Self , "invariant") ; |
|
4295 |
} // OSThreadWaitState() |
|
4296 |
||
4297 |
jt->set_current_waiting_monitor(NULL); |
|
4298 |
||
4299 |
guarantee (_recursions == 0, "invariant") ; |
|
4300 |
_recursions = save; // restore the old recursion count |
|
4301 |
_waiters--; // decrement the number of waiters |
|
4302 |
||
4303 |
// Verify a few postconditions |
|
4304 |
assert (_owner == Self , "invariant") ; |
|
4305 |
assert (_succ != Self , "invariant") ; |
|
4306 |
assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ; |
|
4307 |
||
4308 |
if (SyncFlags & 32) { |
|
4309 |
OrderAccess::fence() ; |
|
4310 |
} |
|
4311 |
||
4312 |
// check if the notification happened |
|
4313 |
if (!WasNotified) { |
|
4314 |
// no, it could be timeout or Thread.interrupt() or both |
|
4315 |
// check for interrupt event, otherwise it is timeout |
|
4316 |
if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) { |
|
4317 |
TEVENT (Wait - throw IEX from epilog) ; |
|
4318 |
THROW(vmSymbols::java_lang_InterruptedException()); |
|
4319 |
} |
|
4320 |
} |
|
4321 |
||
4322 |
// NOTE: Spurious wake up will be consider as timeout. |
|
4323 |
// Monitor notify has precedence over thread interrupt. |
|
4324 |
} |
|
4325 |
||
4326 |
||
4327 |
// Consider: |
|
4328 |
// If the lock is cool (cxq == null && succ == null) and we're on an MP system |
|
4329 |
// then instead of transferring a thread from the WaitSet to the EntryList |
|
4330 |
// we might just dequeue a thread from the WaitSet and directly unpark() it. |
|
4331 |
||
4332 |
void ObjectMonitor::notify(TRAPS) { |
|
4333 |
CHECK_OWNER(); |
|
4334 |
if (_WaitSet == NULL) { |
|
4335 |
TEVENT (Empty-Notify) ; |
|
4336 |
return ; |
|
4337 |
} |
|
4338 |
DTRACE_MONITOR_PROBE(notify, this, object(), THREAD); |
|
4339 |
||
4340 |
int Policy = Knob_MoveNotifyee ; |
|
4341 |
||
4342 |
Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notify") ; |
|
4343 |
ObjectWaiter * iterator = DequeueWaiter() ; |
|
4344 |
if (iterator != NULL) { |
|
4345 |
TEVENT (Notify1 - Transfer) ; |
|
4346 |
guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ; |
|
4347 |
guarantee (iterator->_notified == 0, "invariant") ; |
|
4348 |
// Disposition - what might we do with iterator ? |
|
4349 |
// a. add it directly to the EntryList - either tail or head. |
|
4350 |
// b. push it onto the front of the _cxq. |
|
4351 |
// For now we use (a). |
|
4352 |
if (Policy != 4) { |
|
4353 |
iterator->TState = ObjectWaiter::TS_ENTER ; |
|
4354 |
} |
|
4355 |
iterator->_notified = 1 ; |
|
4356 |
||
4357 |
ObjectWaiter * List = _EntryList ; |
|
4358 |
if (List != NULL) { |
|
4359 |
assert (List->_prev == NULL, "invariant") ; |
|
4360 |
assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
4361 |
assert (List != iterator, "invariant") ; |
|
4362 |
} |
|
4363 |
||
4364 |
if (Policy == 0) { // prepend to EntryList |
|
4365 |
if (List == NULL) { |
|
4366 |
iterator->_next = iterator->_prev = NULL ; |
|
4367 |
_EntryList = iterator ; |
|
4368 |
} else { |
|
4369 |
List->_prev = iterator ; |
|
4370 |
iterator->_next = List ; |
|
4371 |
iterator->_prev = NULL ; |
|
4372 |
_EntryList = iterator ; |
|
4373 |
} |
|
4374 |
} else |
|
4375 |
if (Policy == 1) { // append to EntryList |
|
4376 |
if (List == NULL) { |
|
4377 |
iterator->_next = iterator->_prev = NULL ; |
|
4378 |
_EntryList = iterator ; |
|
4379 |
} else { |
|
4380 |
// CONSIDER: finding the tail currently requires a linear-time walk of |
|
4381 |
// the EntryList. We can make tail access constant-time by converting to |
|
4382 |
// a CDLL instead of using our current DLL. |
|
4383 |
ObjectWaiter * Tail ; |
|
4384 |
for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ; |
|
4385 |
assert (Tail != NULL && Tail->_next == NULL, "invariant") ; |
|
4386 |
Tail->_next = iterator ; |
|
4387 |
iterator->_prev = Tail ; |
|
4388 |
iterator->_next = NULL ; |
|
4389 |
} |
|
4390 |
} else |
|
4391 |
if (Policy == 2) { // prepend to cxq |
|
4392 |
// prepend to cxq |
|
4393 |
if (List == NULL) { |
|
4394 |
iterator->_next = iterator->_prev = NULL ; |
|
4395 |
_EntryList = iterator ; |
|
4396 |
} else { |
|
4397 |
iterator->TState = ObjectWaiter::TS_CXQ ; |
|
4398 |
for (;;) { |
|
4399 |
ObjectWaiter * Front = _cxq ; |
|
4400 |
iterator->_next = Front ; |
|
4401 |
if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) { |
|
4402 |
break ; |
|
4403 |
} |
|
4404 |
} |
|
4405 |
} |
|
4406 |
} else |
|
4407 |
if (Policy == 3) { // append to cxq |
|
4408 |
iterator->TState = ObjectWaiter::TS_CXQ ; |
|
4409 |
for (;;) { |
|
4410 |
ObjectWaiter * Tail ; |
|
4411 |
Tail = _cxq ; |
|
4412 |
if (Tail == NULL) { |
|
4413 |
iterator->_next = NULL ; |
|
4414 |
if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) { |
|
4415 |
break ; |
|
4416 |
} |
|
4417 |
} else { |
|
4418 |
while (Tail->_next != NULL) Tail = Tail->_next ; |
|
4419 |
Tail->_next = iterator ; |
|
4420 |
iterator->_prev = Tail ; |
|
4421 |
iterator->_next = NULL ; |
|
4422 |
break ; |
|
4423 |
} |
|
4424 |
} |
|
4425 |
} else { |
|
4426 |
ParkEvent * ev = iterator->_event ; |
|
4427 |
iterator->TState = ObjectWaiter::TS_RUN ; |
|
4428 |
OrderAccess::fence() ; |
|
4429 |
ev->unpark() ; |
|
4430 |
} |
|
4431 |
||
4432 |
if (Policy < 4) { |
|
4433 |
iterator->wait_reenter_begin(this); |
|
4434 |
} |
|
4435 |
||
4436 |
// _WaitSetLock protects the wait queue, not the EntryList. We could |
|
4437 |
// move the add-to-EntryList operation, above, outside the critical section |
|
4438 |
// protected by _WaitSetLock. In practice that's not useful. With the |
|
4439 |
// exception of wait() timeouts and interrupts the monitor owner |
|
4440 |
// is the only thread that grabs _WaitSetLock. There's almost no contention |
|
4441 |
// on _WaitSetLock so it's not profitable to reduce the length of the |
|
4442 |
// critical section. |
|
4443 |
} |
|
4444 |
||
4445 |
Thread::SpinRelease (&_WaitSetLock) ; |
|
4446 |
||
4447 |
if (iterator != NULL && ObjectSynchronizer::_sync_Notifications != NULL) { |
|
4448 |
ObjectSynchronizer::_sync_Notifications->inc() ; |
|
4449 |
} |
|
4450 |
} |
|
4451 |
||
4452 |
||
4453 |
void ObjectMonitor::notifyAll(TRAPS) { |
|
4454 |
CHECK_OWNER(); |
|
4455 |
ObjectWaiter* iterator; |
|
4456 |
if (_WaitSet == NULL) { |
|
4457 |
TEVENT (Empty-NotifyAll) ; |
|
4458 |
return ; |
|
4459 |
} |
|
4460 |
DTRACE_MONITOR_PROBE(notifyAll, this, object(), THREAD); |
|
4461 |
||
4462 |
int Policy = Knob_MoveNotifyee ; |
|
4463 |
int Tally = 0 ; |
|
4464 |
Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notifyall") ; |
|
4465 |
||
4466 |
for (;;) { |
|
4467 |
iterator = DequeueWaiter () ; |
|
4468 |
if (iterator == NULL) break ; |
|
4469 |
TEVENT (NotifyAll - Transfer1) ; |
|
4470 |
++Tally ; |
|
4471 |
||
4472 |
// Disposition - what might we do with iterator ? |
|
4473 |
// a. add it directly to the EntryList - either tail or head. |
|
4474 |
// b. push it onto the front of the _cxq. |
|
4475 |
// For now we use (a). |
|
4476 |
// |
|
4477 |
// TODO-FIXME: currently notifyAll() transfers the waiters one-at-a-time from the waitset |
|
4478 |
// to the EntryList. This could be done more efficiently with a single bulk transfer, |
|
4479 |
// but in practice it's not time-critical. Beware too, that in prepend-mode we invert the |
|
4480 |
// order of the waiters. Lets say that the waitset is "ABCD" and the EntryList is "XYZ". |
|
4481 |
// After a notifyAll() in prepend mode the waitset will be empty and the EntryList will |
|
4482 |
// be "DCBAXYZ". |
|
4483 |
||
4484 |
guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ; |
|
4485 |
guarantee (iterator->_notified == 0, "invariant") ; |
|
4486 |
iterator->_notified = 1 ; |
|
4487 |
if (Policy != 4) { |
|
4488 |
iterator->TState = ObjectWaiter::TS_ENTER ; |
|
4489 |
} |
|
4490 |
||
4491 |
ObjectWaiter * List = _EntryList ; |
|
4492 |
if (List != NULL) { |
|
4493 |
assert (List->_prev == NULL, "invariant") ; |
|
4494 |
assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
4495 |
assert (List != iterator, "invariant") ; |
|
4496 |
} |
|
4497 |
||
4498 |
if (Policy == 0) { // prepend to EntryList |
|
4499 |
if (List == NULL) { |
|
4500 |
iterator->_next = iterator->_prev = NULL ; |
|
4501 |
_EntryList = iterator ; |
|
4502 |
} else { |
|
4503 |
List->_prev = iterator ; |
|
4504 |
iterator->_next = List ; |
|
4505 |
iterator->_prev = NULL ; |
|
4506 |
_EntryList = iterator ; |
|
4507 |
} |
|
4508 |
} else |
|
4509 |
if (Policy == 1) { // append to EntryList |
|
4510 |
if (List == NULL) { |
|
4511 |
iterator->_next = iterator->_prev = NULL ; |
|
4512 |
_EntryList = iterator ; |
|
4513 |
} else { |
|
4514 |
// CONSIDER: finding the tail currently requires a linear-time walk of |
|
4515 |
// the EntryList. We can make tail access constant-time by converting to |
|
4516 |
// a CDLL instead of using our current DLL. |
|
4517 |
ObjectWaiter * Tail ; |
|
4518 |
for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ; |
|
4519 |
assert (Tail != NULL && Tail->_next == NULL, "invariant") ; |
|
4520 |
Tail->_next = iterator ; |
|
4521 |
iterator->_prev = Tail ; |
|
4522 |
iterator->_next = NULL ; |
|
4523 |
} |
|
4524 |
} else |
|
4525 |
if (Policy == 2) { // prepend to cxq |
|
4526 |
// prepend to cxq |
|
4527 |
iterator->TState = ObjectWaiter::TS_CXQ ; |
|
4528 |
for (;;) { |
|
4529 |
ObjectWaiter * Front = _cxq ; |
|
4530 |
iterator->_next = Front ; |
|
4531 |
if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) { |
|
4532 |
break ; |
|
4533 |
} |
|
4534 |
} |
|
4535 |
} else |
|
4536 |
if (Policy == 3) { // append to cxq |
|
4537 |
iterator->TState = ObjectWaiter::TS_CXQ ; |
|
4538 |
for (;;) { |
|
4539 |
ObjectWaiter * Tail ; |
|
4540 |
Tail = _cxq ; |
|
4541 |
if (Tail == NULL) { |
|
4542 |
iterator->_next = NULL ; |
|
4543 |
if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) { |
|
4544 |
break ; |
|
4545 |
} |
|
4546 |
} else { |
|
4547 |
while (Tail->_next != NULL) Tail = Tail->_next ; |
|
4548 |
Tail->_next = iterator ; |
|
4549 |
iterator->_prev = Tail ; |
|
4550 |
iterator->_next = NULL ; |
|
4551 |
break ; |
|
4552 |
} |
|
4553 |
} |
|
4554 |
} else { |
|
4555 |
ParkEvent * ev = iterator->_event ; |
|
4556 |
iterator->TState = ObjectWaiter::TS_RUN ; |
|
4557 |
OrderAccess::fence() ; |
|
4558 |
ev->unpark() ; |
|
4559 |
} |
|
4560 |
||
4561 |
if (Policy < 4) { |
|
4562 |
iterator->wait_reenter_begin(this); |
|
4563 |
} |
|
4564 |
||
4565 |
// _WaitSetLock protects the wait queue, not the EntryList. We could |
|
4566 |
// move the add-to-EntryList operation, above, outside the critical section |
|
4567 |
// protected by _WaitSetLock. In practice that's not useful. With the |
|
4568 |
// exception of wait() timeouts and interrupts the monitor owner |
|
4569 |
// is the only thread that grabs _WaitSetLock. There's almost no contention |
|
4570 |
// on _WaitSetLock so it's not profitable to reduce the length of the |
|
4571 |
// critical section. |
|
4572 |
} |
|
4573 |
||
4574 |
Thread::SpinRelease (&_WaitSetLock) ; |
|
4575 |
||
4576 |
if (Tally != 0 && ObjectSynchronizer::_sync_Notifications != NULL) { |
|
4577 |
ObjectSynchronizer::_sync_Notifications->inc(Tally) ; |
|
4578 |
} |
|
4579 |
} |
|
4580 |
||
4581 |
// check_slow() is a misnomer. It's called to simply to throw an IMSX exception. |
|
4582 |
// TODO-FIXME: remove check_slow() -- it's likely dead. |
|
4583 |
||
4584 |
void ObjectMonitor::check_slow(TRAPS) { |
|
4585 |
TEVENT (check_slow - throw IMSX) ; |
|
4586 |
assert(THREAD != _owner && !THREAD->is_lock_owned((address) _owner), "must not be owner"); |
|
4587 |
THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), "current thread not owner"); |
|
4588 |
} |
|
4589 |
||
4590 |
||
4591 |
// ------------------------------------------------------------------------- |
|
4592 |
// The raw monitor subsystem is entirely distinct from normal |
|
4593 |
// java-synchronization or jni-synchronization. raw monitors are not |
|
4594 |
// associated with objects. They can be implemented in any manner |
|
4595 |
// that makes sense. The original implementors decided to piggy-back |
|
4596 |
// the raw-monitor implementation on the existing Java objectMonitor mechanism. |
|
4597 |
// This flaw needs to fixed. We should reimplement raw monitors as sui-generis. |
|
4598 |
// Specifically, we should not implement raw monitors via java monitors. |
|
4599 |
// Time permitting, we should disentangle and deconvolve the two implementations |
|
4600 |
// and move the resulting raw monitor implementation over to the JVMTI directories. |
|
4601 |
// Ideally, the raw monitor implementation would be built on top of |
|
4602 |
// park-unpark and nothing else. |
|
4603 |
// |
|
4604 |
// raw monitors are used mainly by JVMTI |
|
4605 |
// The raw monitor implementation borrows the ObjectMonitor structure, |
|
4606 |
// but the operators are degenerate and extremely simple. |
|
4607 |
// |
|
4608 |
// Mixed use of a single objectMonitor instance -- as both a raw monitor |
|
4609 |
// and a normal java monitor -- is not permissible. |
|
4610 |
// |
|
4611 |
// Note that we use the single RawMonitor_lock to protect queue operations for |
|
4612 |
// _all_ raw monitors. This is a scalability impediment, but since raw monitor usage |
|
4613 |
// is deprecated and rare, this is not of concern. The RawMonitor_lock can not |
|
4614 |
// be held indefinitely. The critical sections must be short and bounded. |
|
4615 |
// |
|
4616 |
// ------------------------------------------------------------------------- |
|
4617 |
||
4618 |
int ObjectMonitor::SimpleEnter (Thread * Self) { |
|
4619 |
for (;;) { |
|
4620 |
if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) { |
|
4621 |
return OS_OK ; |
|
4622 |
} |
|
4623 |
||
4624 |
ObjectWaiter Node (Self) ; |
|
4625 |
Self->_ParkEvent->reset() ; // strictly optional |
|
4626 |
Node.TState = ObjectWaiter::TS_ENTER ; |
|
4627 |
||
4628 |
RawMonitor_lock->lock_without_safepoint_check() ; |
|
4629 |
Node._next = _EntryList ; |
|
4630 |
_EntryList = &Node ; |
|
4631 |
OrderAccess::fence() ; |
|
4632 |
if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) { |
|
4633 |
_EntryList = Node._next ; |
|
4634 |
RawMonitor_lock->unlock() ; |
|
4635 |
return OS_OK ; |
|
4636 |
} |
|
4637 |
RawMonitor_lock->unlock() ; |
|
4638 |
while (Node.TState == ObjectWaiter::TS_ENTER) { |
|
4639 |
Self->_ParkEvent->park() ; |
|
4640 |
} |
|
4641 |
} |
|
4642 |
} |
|
4643 |
||
4644 |
int ObjectMonitor::SimpleExit (Thread * Self) { |
|
4645 |
guarantee (_owner == Self, "invariant") ; |
|
4646 |
OrderAccess::release_store_ptr (&_owner, NULL) ; |
|
4647 |
OrderAccess::fence() ; |
|
4648 |
if (_EntryList == NULL) return OS_OK ; |
|
4649 |
ObjectWaiter * w ; |
|
4650 |
||
4651 |
RawMonitor_lock->lock_without_safepoint_check() ; |
|
4652 |
w = _EntryList ; |
|
4653 |
if (w != NULL) { |
|
4654 |
_EntryList = w->_next ; |
|
4655 |
} |
|
4656 |
RawMonitor_lock->unlock() ; |
|
4657 |
if (w != NULL) { |
|
4658 |
guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ; |
|
4659 |
ParkEvent * ev = w->_event ; |
|
4660 |
w->TState = ObjectWaiter::TS_RUN ; |
|
4661 |
OrderAccess::fence() ; |
|
4662 |
ev->unpark() ; |
|
4663 |
} |
|
4664 |
return OS_OK ; |
|
4665 |
} |
|
4666 |
||
4667 |
int ObjectMonitor::SimpleWait (Thread * Self, jlong millis) { |
|
4668 |
guarantee (_owner == Self , "invariant") ; |
|
4669 |
guarantee (_recursions == 0, "invariant") ; |
|
4670 |
||
4671 |
ObjectWaiter Node (Self) ; |
|
4672 |
Node._notified = 0 ; |
|
4673 |
Node.TState = ObjectWaiter::TS_WAIT ; |
|
4674 |
||
4675 |
RawMonitor_lock->lock_without_safepoint_check() ; |
|
4676 |
Node._next = _WaitSet ; |
|
4677 |
_WaitSet = &Node ; |
|
4678 |
RawMonitor_lock->unlock() ; |
|
4679 |
||
4680 |
SimpleExit (Self) ; |
|
4681 |
guarantee (_owner != Self, "invariant") ; |
|
4682 |
||
4683 |
int ret = OS_OK ; |
|
4684 |
if (millis <= 0) { |
|
4685 |
Self->_ParkEvent->park(); |
|
4686 |
} else { |
|
4687 |
ret = Self->_ParkEvent->park(millis); |
|
4688 |
} |
|
4689 |
||
4690 |
// If thread still resides on the waitset then unlink it. |
|
4691 |
// Double-checked locking -- the usage is safe in this context |
|
4692 |
// as we TState is volatile and the lock-unlock operators are |
|
4693 |
// serializing (barrier-equivalent). |
|
4694 |
||
4695 |
if (Node.TState == ObjectWaiter::TS_WAIT) { |
|
4696 |
RawMonitor_lock->lock_without_safepoint_check() ; |
|
4697 |
if (Node.TState == ObjectWaiter::TS_WAIT) { |
|
4698 |
// Simple O(n) unlink, but performance isn't critical here. |
|
4699 |
ObjectWaiter * p ; |
|
4700 |
ObjectWaiter * q = NULL ; |
|
4701 |
for (p = _WaitSet ; p != &Node; p = p->_next) { |
|
4702 |
q = p ; |
|
4703 |
} |
|
4704 |
guarantee (p == &Node, "invariant") ; |
|
4705 |
if (q == NULL) { |
|
4706 |
guarantee (p == _WaitSet, "invariant") ; |
|
4707 |
_WaitSet = p->_next ; |
|
4708 |
} else { |
|
4709 |
guarantee (p == q->_next, "invariant") ; |
|
4710 |
q->_next = p->_next ; |
|
4711 |
} |
|
4712 |
Node.TState = ObjectWaiter::TS_RUN ; |
|
4713 |
} |
|
4714 |
RawMonitor_lock->unlock() ; |
|
4715 |
} |
|
4716 |
||
4717 |
guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ; |
|
4718 |
SimpleEnter (Self) ; |
|
4719 |
||
4720 |
guarantee (_owner == Self, "invariant") ; |
|
4721 |
guarantee (_recursions == 0, "invariant") ; |
|
4722 |
return ret ; |
|
4723 |
} |
|
4724 |
||
4725 |
int ObjectMonitor::SimpleNotify (Thread * Self, bool All) { |
|
4726 |
guarantee (_owner == Self, "invariant") ; |
|
4727 |
if (_WaitSet == NULL) return OS_OK ; |
|
4728 |
||
4729 |
// We have two options: |
|
4730 |
// A. Transfer the threads from the WaitSet to the EntryList |
|
4731 |
// B. Remove the thread from the WaitSet and unpark() it. |
|
4732 |
// |
|
4733 |
// We use (B), which is crude and results in lots of futile |
|
4734 |
// context switching. In particular (B) induces lots of contention. |
|
4735 |
||
4736 |
ParkEvent * ev = NULL ; // consider using a small auto array ... |
|
4737 |
RawMonitor_lock->lock_without_safepoint_check() ; |
|
4738 |
for (;;) { |
|
4739 |
ObjectWaiter * w = _WaitSet ; |
|
4740 |
if (w == NULL) break ; |
|
4741 |
_WaitSet = w->_next ; |
|
4742 |
if (ev != NULL) { ev->unpark(); ev = NULL; } |
|
4743 |
ev = w->_event ; |
|
4744 |
OrderAccess::loadstore() ; |
|
4745 |
w->TState = ObjectWaiter::TS_RUN ; |
|
4746 |
OrderAccess::storeload(); |
|
4747 |
if (!All) break ; |
|
4748 |
} |
|
4749 |
RawMonitor_lock->unlock() ; |
|
4750 |
if (ev != NULL) ev->unpark(); |
|
4751 |
return OS_OK ; |
|
4752 |
} |
|
4753 |
||
4754 |
// Any JavaThread will enter here with state _thread_blocked |
|
4755 |
int ObjectMonitor::raw_enter(TRAPS) { |
|
4756 |
TEVENT (raw_enter) ; |
|
4757 |
void * Contended ; |
|
4758 |
||
4759 |
// don't enter raw monitor if thread is being externally suspended, it will |
|
4760 |
// surprise the suspender if a "suspended" thread can still enter monitor |
|
4761 |
JavaThread * jt = (JavaThread *)THREAD; |
|
4762 |
if (THREAD->is_Java_thread()) { |
|
4763 |
jt->SR_lock()->lock_without_safepoint_check(); |
|
4764 |
while (jt->is_external_suspend()) { |
|
4765 |
jt->SR_lock()->unlock(); |
|
4766 |
jt->java_suspend_self(); |
|
4767 |
jt->SR_lock()->lock_without_safepoint_check(); |
|
4768 |
} |
|
4769 |
// guarded by SR_lock to avoid racing with new external suspend requests. |
|
4770 |
Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ; |
|
4771 |
jt->SR_lock()->unlock(); |
|
4772 |
} else { |
|
4773 |
Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ; |
|
4774 |
} |
|
4775 |
||
4776 |
if (Contended == THREAD) { |
|
4777 |
_recursions ++ ; |
|
4778 |
return OM_OK ; |
|
4779 |
} |
|
4780 |
||
4781 |
if (Contended == NULL) { |
|
4782 |
guarantee (_owner == THREAD, "invariant") ; |
|
4783 |
guarantee (_recursions == 0, "invariant") ; |
|
4784 |
return OM_OK ; |
|
4785 |
} |
|
4786 |
||
4787 |
THREAD->set_current_pending_monitor(this); |
|
4788 |
||
4789 |
if (!THREAD->is_Java_thread()) { |
|
4790 |
// No other non-Java threads besides VM thread would acquire |
|
4791 |
// a raw monitor. |
|
4792 |
assert(THREAD->is_VM_thread(), "must be VM thread"); |
|
4793 |
SimpleEnter (THREAD) ; |
|
4794 |
} else { |
|
4795 |
guarantee (jt->thread_state() == _thread_blocked, "invariant") ; |
|
4796 |
for (;;) { |
|
4797 |
jt->set_suspend_equivalent(); |
|
4798 |
// cleared by handle_special_suspend_equivalent_condition() or |
|
4799 |
// java_suspend_self() |
|
4800 |
SimpleEnter (THREAD) ; |
|
4801 |
||
4802 |
// were we externally suspended while we were waiting? |
|
4803 |
if (!jt->handle_special_suspend_equivalent_condition()) break ; |
|
4804 |
||
4805 |
// This thread was externally suspended |
|
4806 |
// |
|
4807 |
// This logic isn't needed for JVMTI raw monitors, |
|
4808 |
// but doesn't hurt just in case the suspend rules change. This |
|
4809 |
// logic is needed for the ObjectMonitor.wait() reentry phase. |
|
4810 |
// We have reentered the contended monitor, but while we were |
|
4811 |
// waiting another thread suspended us. We don't want to reenter |
|
4812 |
// the monitor while suspended because that would surprise the |
|
4813 |
// thread that suspended us. |
|
4814 |
// |
|
4815 |
// Drop the lock - |
|
4816 |
SimpleExit (THREAD) ; |
|
4817 |
||
4818 |
jt->java_suspend_self(); |
|
4819 |
} |
|
4820 |
||
4821 |
assert(_owner == THREAD, "Fatal error with monitor owner!"); |
|
4822 |
assert(_recursions == 0, "Fatal error with monitor recursions!"); |
|
4823 |
} |
|
4824 |
||
4825 |
THREAD->set_current_pending_monitor(NULL); |
|
4826 |
guarantee (_recursions == 0, "invariant") ; |
|
4827 |
return OM_OK; |
|
4828 |
} |
|
4829 |
||
4830 |
// Used mainly for JVMTI raw monitor implementation |
|
4831 |
// Also used for ObjectMonitor::wait(). |
|
4832 |
int ObjectMonitor::raw_exit(TRAPS) { |
|
4833 |
TEVENT (raw_exit) ; |
|
4834 |
if (THREAD != _owner) { |
|
4835 |
return OM_ILLEGAL_MONITOR_STATE; |
|
4836 |
} |
|
4837 |
if (_recursions > 0) { |
|
4838 |
--_recursions ; |
|
4839 |
return OM_OK ; |
|
4840 |
} |
|
4841 |
||
4842 |
void * List = _EntryList ; |
|
4843 |
SimpleExit (THREAD) ; |
|
4844 |
||
4845 |
return OM_OK; |
|
4846 |
} |
|
4847 |
||
4848 |
// Used for JVMTI raw monitor implementation. |
|
4849 |
// All JavaThreads will enter here with state _thread_blocked |
|
4850 |
||
4851 |
int ObjectMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) { |
|
4852 |
TEVENT (raw_wait) ; |
|
4853 |
if (THREAD != _owner) { |
|
4854 |
return OM_ILLEGAL_MONITOR_STATE; |
|
4855 |
} |
|
4856 |
||
4857 |
// To avoid spurious wakeups we reset the parkevent -- This is strictly optional. |
|
4858 |
// The caller must be able to tolerate spurious returns from raw_wait(). |
|
4859 |
THREAD->_ParkEvent->reset() ; |
|
4860 |
OrderAccess::fence() ; |
|
4861 |
||
4862 |
// check interrupt event |
|
4863 |
if (interruptible && Thread::is_interrupted(THREAD, true)) { |
|
4864 |
return OM_INTERRUPTED; |
|
4865 |
} |
|
4866 |
||
4867 |
intptr_t save = _recursions ; |
|
4868 |
_recursions = 0 ; |
|
4869 |
_waiters ++ ; |
|
4870 |
if (THREAD->is_Java_thread()) { |
|
4871 |
guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ; |
|
4872 |
((JavaThread *)THREAD)->set_suspend_equivalent(); |
|
4873 |
} |
|
4874 |
int rv = SimpleWait (THREAD, millis) ; |
|
4875 |
_recursions = save ; |
|
4876 |
_waiters -- ; |
|
4877 |
||
4878 |
guarantee (THREAD == _owner, "invariant") ; |
|
4879 |
if (THREAD->is_Java_thread()) { |
|
4880 |
JavaThread * jSelf = (JavaThread *) THREAD ; |
|
4881 |
for (;;) { |
|
4882 |
if (!jSelf->handle_special_suspend_equivalent_condition()) break ; |
|
4883 |
SimpleExit (THREAD) ; |
|
4884 |
jSelf->java_suspend_self(); |
|
4885 |
SimpleEnter (THREAD) ; |
|
4886 |
jSelf->set_suspend_equivalent() ; |
|
4887 |
} |
|
4888 |
} |
|
4889 |
guarantee (THREAD == _owner, "invariant") ; |
|
4890 |
||
4891 |
if (interruptible && Thread::is_interrupted(THREAD, true)) { |
|
4892 |
return OM_INTERRUPTED; |
|
4893 |
} |
|
4894 |
return OM_OK ; |
|
4895 |
} |
|
4896 |
||
4897 |
int ObjectMonitor::raw_notify(TRAPS) { |
|
4898 |
TEVENT (raw_notify) ; |
|
4899 |
if (THREAD != _owner) { |
|
4900 |
return OM_ILLEGAL_MONITOR_STATE; |
|
4901 |
} |
|
4902 |
SimpleNotify (THREAD, false) ; |
|
4903 |
return OM_OK; |
|
4904 |
} |
|
4905 |
||
4906 |
int ObjectMonitor::raw_notifyAll(TRAPS) { |
|
4907 |
TEVENT (raw_notifyAll) ; |
|
4908 |
if (THREAD != _owner) { |
|
4909 |
return OM_ILLEGAL_MONITOR_STATE; |
|
4910 |
} |
|
4911 |
SimpleNotify (THREAD, true) ; |
|
4912 |
return OM_OK; |
|
4913 |
} |
|
4914 |
||
4915 |
#ifndef PRODUCT |
|
4916 |
void ObjectMonitor::verify() { |
|
4917 |
} |
|
4918 |
||
4919 |
void ObjectMonitor::print() { |
|
4920 |
} |
|
4921 |
#endif |
|
4922 |
||
4923 |
//------------------------------------------------------------------------------ |
|
4924 |
// Non-product code |
|
4925 |
||
4926 |
#ifndef PRODUCT |
|
4927 |
||
4928 |
void ObjectSynchronizer::trace_locking(Handle locking_obj, bool is_compiled, |
|
4929 |
bool is_method, bool is_locking) { |
|
4930 |
// Don't know what to do here |
|
4931 |
} |
|
4932 |
||
4933 |
// Verify all monitors in the monitor cache, the verification is weak. |
|
4934 |
void ObjectSynchronizer::verify() { |
|
4935 |
ObjectMonitor* block = gBlockList; |
|
4936 |
ObjectMonitor* mid; |
|
4937 |
while (block) { |
|
4938 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
4939 |
for (int i = 1; i < _BLOCKSIZE; i++) { |
|
4940 |
mid = block + i; |
|
4941 |
oop object = (oop) mid->object(); |
|
4942 |
if (object != NULL) { |
|
4943 |
mid->verify(); |
|
4944 |
} |
|
4945 |
} |
|
4946 |
block = (ObjectMonitor*) block->FreeNext; |
|
4947 |
} |
|
4948 |
} |
|
4949 |
||
4950 |
// Check if monitor belongs to the monitor cache |
|
4951 |
// The list is grow-only so it's *relatively* safe to traverse |
|
4952 |
// the list of extant blocks without taking a lock. |
|
4953 |
||
4954 |
int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) { |
|
4955 |
ObjectMonitor* block = gBlockList; |
|
4956 |
||
4957 |
while (block) { |
|
4958 |
assert(block->object() == CHAINMARKER, "must be a block header"); |
|
4959 |
if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) { |
|
4960 |
address mon = (address) monitor; |
|
4961 |
address blk = (address) block; |
|
4962 |
size_t diff = mon - blk; |
|
4963 |
assert((diff % sizeof(ObjectMonitor)) == 0, "check"); |
|
4964 |
return 1; |
|
4965 |
} |
|
4966 |
block = (ObjectMonitor*) block->FreeNext; |
|
4967 |
} |
|
4968 |
return 0; |
|
4969 |
} |
|
4970 |
||
4971 |
#endif |