jdk-sandbox: comparison hotspot/src/share/vm/runtime/objectMonitor.cpp

equal deleted inserted replaced

-:11c11e616b91
+:dc9b63952682
+/*
+* Copyright (c) 1998, 2009, Oracle and/or its affiliates. All rights reserved.
+* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+*
+* This code is free software; you can redistribute it and/or modify it
+* under the terms of the GNU General Public License version 2 only, as
+* published by the Free Software Foundation.
+*
+* This code is distributed in the hope that it will be useful, but WITHOUT
+* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+* version 2 for more details (a copy is included in the LICENSE file that
+* accompanied this code).
+*
+* You should have received a copy of the GNU General Public License version
+* 2 along with this work; if not, write to the Free Software Foundation,
+* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+*
+* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+* or visit www.oracle.com if you need additional information or have any
+* questions.
+*
+*/
+# include "incls/_precompiled.incl"
+# include "incls/_objectMonitor.cpp.incl"
+#if defined(__GNUC__) && !defined(IA64)
+// Need to inhibit inlining for older versions of GCC to avoid build-time failures
+#define ATTR __attribute__((noinline))
+#else
+#define ATTR
+#endif
+#ifdef DTRACE_ENABLED
+// Only bother with this argument setup if dtrace is available
+// TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
+HS_DTRACE_PROBE_DECL4(hotspot, monitor__notify,
+jlong, uintptr_t, char*, int);
+HS_DTRACE_PROBE_DECL4(hotspot, monitor__notifyAll,
+jlong, uintptr_t, char*, int);
+HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__enter,
+jlong, uintptr_t, char*, int);
+HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__entered,
+jlong, uintptr_t, char*, int);
+HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__exit,
+jlong, uintptr_t, char*, int);
+#define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread)                      \
+char* bytes = NULL;                                                      \
+int len = 0;                                                             \
+jlong jtid = SharedRuntime::get_java_tid(thread);                        \
+symbolOop klassname = ((oop)(klassOop))->klass()->klass_part()->name();  \
+if (klassname != NULL) {                                                 \
+bytes = (char*)klassname->bytes();                                     \
+len = klassname->utf8_length();                                        \
+}
+#define DTRACE_MONITOR_WAIT_PROBE(monitor, klassOop, thread, millis)       \
+{                                                                        \
+if (DTraceMonitorProbes) {                                            \
+DTRACE_MONITOR_PROBE_COMMON(klassOop, thread);                       \
+HS_DTRACE_PROBE5(hotspot, monitor__wait, jtid,                       \
+(monitor), bytes, len, (millis));                   \
+}                                                                      \
+}
+#define DTRACE_MONITOR_PROBE(probe, monitor, klassOop, thread)             \
+{                                                                        \
+if (DTraceMonitorProbes) {                                            \
+DTRACE_MONITOR_PROBE_COMMON(klassOop, thread);                       \
+HS_DTRACE_PROBE4(hotspot, monitor__##probe, jtid,                    \
+(uintptr_t)(monitor), bytes, len);                  \
+}                                                                      \
+}
+#else //  ndef DTRACE_ENABLED
+#define DTRACE_MONITOR_WAIT_PROBE(klassOop, thread, millis, mon)    {;}
+#define DTRACE_MONITOR_PROBE(probe, klassOop, thread, mon)          {;}
+#endif // ndef DTRACE_ENABLED
+// Tunables ...
+// The knob* variables are effectively final.  Once set they should
+// never be modified hence.  Consider using __read_mostly with GCC.
+int ObjectMonitor::Knob_Verbose    = 0 ;
+int ObjectMonitor::Knob_SpinLimit  = 5000 ;    // derived by an external tool -
+static int Knob_LogSpins           = 0 ;       // enable jvmstat tally for spins
+static int Knob_HandOff            = 0 ;
+static int Knob_ReportSettings     = 0 ;
+static int Knob_SpinBase           = 0 ;       // Floor AKA SpinMin
+static int Knob_SpinBackOff        = 0 ;       // spin-loop backoff
+static int Knob_CASPenalty         = -1 ;      // Penalty for failed CAS
+static int Knob_OXPenalty          = -1 ;      // Penalty for observed _owner change
+static int Knob_SpinSetSucc        = 1 ;       // spinners set the _succ field
+static int Knob_SpinEarly          = 1 ;
+static int Knob_SuccEnabled        = 1 ;       // futile wake throttling
+static int Knob_SuccRestrict       = 0 ;       // Limit successors + spinners to at-most-one
+static int Knob_MaxSpinners        = -1 ;      // Should be a function of # CPUs
+static int Knob_Bonus              = 100 ;     // spin success bonus
+static int Knob_BonusB             = 100 ;     // spin success bonus
+static int Knob_Penalty            = 200 ;     // spin failure penalty
+static int Knob_Poverty            = 1000 ;
+static int Knob_SpinAfterFutile    = 1 ;       // Spin after returning from park()
+static int Knob_FixedSpin          = 0 ;
+static int Knob_OState             = 3 ;       // Spinner checks thread state of _owner
+static int Knob_UsePause           = 1 ;
+static int Knob_ExitPolicy         = 0 ;
+static int Knob_PreSpin            = 10 ;      // 20-100 likely better
+static int Knob_ResetEvent         = 0 ;
+static int BackOffMask             = 0 ;
+static int Knob_FastHSSEC          = 0 ;
+static int Knob_MoveNotifyee       = 2 ;       // notify() - disposition of notifyee
+static int Knob_QMode              = 0 ;       // EntryList-cxq policy - queue discipline
+static volatile int InitDone       = 0 ;
+#define TrySpin TrySpin_VaryDuration
+// -----------------------------------------------------------------------------
+// Theory of operations -- Monitors lists, thread residency, etc:
+//
+// * A thread acquires ownership of a monitor by successfully
+//   CAS()ing the _owner field from null to non-null.
+//
+// * Invariant: A thread appears on at most one monitor list --
+//   cxq, EntryList or WaitSet -- at any one time.
+//
+// * Contending threads "push" themselves onto the cxq with CAS
+//   and then spin/park.
+//
+// * After a contending thread eventually acquires the lock it must
+//   dequeue itself from either the EntryList or the cxq.
+//
+// * The exiting thread identifies and unparks an "heir presumptive"
+//   tentative successor thread on the EntryList.  Critically, the
+//   exiting thread doesn't unlink the successor thread from the EntryList.
+//   After having been unparked, the wakee will recontend for ownership of
+//   the monitor.   The successor (wakee) will either acquire the lock or
+//   re-park itself.
+//
+//   Succession is provided for by a policy of competitive handoff.
+//   The exiting thread does _not_ grant or pass ownership to the
+//   successor thread.  (This is also referred to as "handoff" succession").
+//   Instead the exiting thread releases ownership and possibly wakes
+//   a successor, so the successor can (re)compete for ownership of the lock.
+//   If the EntryList is empty but the cxq is populated the exiting
+//   thread will drain the cxq into the EntryList.  It does so by
+//   by detaching the cxq (installing null with CAS) and folding
+//   the threads from the cxq into the EntryList.  The EntryList is
+//   doubly linked, while the cxq is singly linked because of the
+//   CAS-based "push" used to enqueue recently arrived threads (RATs).
+//
+// * Concurrency invariants:
+//
+//   -- only the monitor owner may access or mutate the EntryList.
+//      The mutex property of the monitor itself protects the EntryList
+//      from concurrent interference.
+//   -- Only the monitor owner may detach the cxq.
+//
+// * The monitor entry list operations avoid locks, but strictly speaking
+//   they're not lock-free.  Enter is lock-free, exit is not.
+//   See http://j2se.east/~dice/PERSIST/040825-LockFreeQueues.html
+//
+// * The cxq can have multiple concurrent "pushers" but only one concurrent
+//   detaching thread.  This mechanism is immune from the ABA corruption.
+//   More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
+//
+// * Taken together, the cxq and the EntryList constitute or form a
+//   single logical queue of threads stalled trying to acquire the lock.
+//   We use two distinct lists to improve the odds of a constant-time
+//   dequeue operation after acquisition (in the ::enter() epilog) and
+//   to reduce heat on the list ends.  (c.f. Michael Scott's "2Q" algorithm).
+//   A key desideratum is to minimize queue & monitor metadata manipulation
+//   that occurs while holding the monitor lock -- that is, we want to
+//   minimize monitor lock holds times.  Note that even a small amount of
+//   fixed spinning will greatly reduce the # of enqueue-dequeue operations
+//   on EntryList|cxq.  That is, spinning relieves contention on the "inner"
+//   locks and monitor metadata.
+//
+//   Cxq points to the the set of Recently Arrived Threads attempting entry.
+//   Because we push threads onto _cxq with CAS, the RATs must take the form of
+//   a singly-linked LIFO.  We drain _cxq into EntryList  at unlock-time when
+//   the unlocking thread notices that EntryList is null but _cxq is != null.
+//
+//   The EntryList is ordered by the prevailing queue discipline and
+//   can be organized in any convenient fashion, such as a doubly-linked list or
+//   a circular doubly-linked list.  Critically, we want insert and delete operations
+//   to operate in constant-time.  If we need a priority queue then something akin
+//   to Solaris' sleepq would work nicely.  Viz.,
+//   http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
+//   Queue discipline is enforced at ::exit() time, when the unlocking thread
+//   drains the cxq into the EntryList, and orders or reorders the threads on the
+//   EntryList accordingly.
+//
+//   Barring "lock barging", this mechanism provides fair cyclic ordering,
+//   somewhat similar to an elevator-scan.
+//
+// * The monitor synchronization subsystem avoids the use of native
+//   synchronization primitives except for the narrow platform-specific
+//   park-unpark abstraction.  See the comments in os_solaris.cpp regarding
+//   the semantics of park-unpark.  Put another way, this monitor implementation
+//   depends only on atomic operations and park-unpark.  The monitor subsystem
+//   manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
+//   underlying OS manages the READY<->RUN transitions.
+//
+// * Waiting threads reside on the WaitSet list -- wait() puts
+//   the caller onto the WaitSet.
+//
+// * notify() or notifyAll() simply transfers threads from the WaitSet to
+//   either the EntryList or cxq.  Subsequent exit() operations will
+//   unpark the notifyee.  Unparking a notifee in notify() is inefficient -
+//   it's likely the notifyee would simply impale itself on the lock held
+//   by the notifier.
+//
+// * An interesting alternative is to encode cxq as (List,LockByte) where
+//   the LockByte is 0 iff the monitor is owned.  _owner is simply an auxiliary
+//   variable, like _recursions, in the scheme.  The threads or Events that form
+//   the list would have to be aligned in 256-byte addresses.  A thread would
+//   try to acquire the lock or enqueue itself with CAS, but exiting threads
+//   could use a 1-0 protocol and simply STB to set the LockByte to 0.
+//   Note that is is *not* word-tearing, but it does presume that full-word
+//   CAS operations are coherent with intermix with STB operations.  That's true
+//   on most common processors.
+//
+// * See also http://blogs.sun.com/dave
+// -----------------------------------------------------------------------------
+// Enter support
+bool ObjectMonitor::try_enter(Thread* THREAD) {
+if (THREAD != _owner) {
+if (THREAD->is_lock_owned ((address)_owner)) {
+assert(_recursions == 0, "internal state error");
+_owner = THREAD ;
+_recursions = 1 ;
+OwnerIsThread = 1 ;
+return true;
+}
+if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
+return false;
+}
+return true;
+} else {
+_recursions++;
+return true;
+}
+}
+void ATTR ObjectMonitor::enter(TRAPS) {
+// The following code is ordered to check the most common cases first
+// and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
+Thread * const Self = THREAD ;
+void * cur ;
+cur = Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
+if (cur == NULL) {
+// Either ASSERT _recursions == 0 or explicitly set _recursions = 0.
+assert (_recursions == 0   , "invariant") ;
+assert (_owner      == Self, "invariant") ;
+// CONSIDER: set or assert OwnerIsThread == 1
+return ;
+}
+if (cur == Self) {
+// TODO-FIXME: check for integer overflow!  BUGID 6557169.
+_recursions ++ ;
+return ;
+}
+if (Self->is_lock_owned ((address)cur)) {
+assert (_recursions == 0, "internal state error");
+_recursions = 1 ;
+// Commute owner from a thread-specific on-stack BasicLockObject address to
+// a full-fledged "Thread *".
+_owner = Self ;
+OwnerIsThread = 1 ;
+return ;
+}
+// We've encountered genuine contention.
+assert (Self->_Stalled == 0, "invariant") ;
+Self->_Stalled = intptr_t(this) ;
+// Try one round of spinning *before* enqueueing Self
+// and before going through the awkward and expensive state
+// transitions.  The following spin is strictly optional ...
+// Note that if we acquire the monitor from an initial spin
+// we forgo posting JVMTI events and firing DTRACE probes.
+if (Knob_SpinEarly && TrySpin (Self) > 0) {
+assert (_owner == Self      , "invariant") ;
+assert (_recursions == 0    , "invariant") ;
+assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
+Self->_Stalled = 0 ;
+return ;
+}
+assert (_owner != Self          , "invariant") ;
+assert (_succ  != Self          , "invariant") ;
+assert (Self->is_Java_thread()  , "invariant") ;
+JavaThread * jt = (JavaThread *) Self ;
+assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
+assert (jt->thread_state() != _thread_blocked   , "invariant") ;
+assert (this->object() != NULL  , "invariant") ;
+assert (_count >= 0, "invariant") ;
+// Prevent deflation at STW-time.  See deflate_idle_monitors() and is_busy().
+// Ensure the object-monitor relationship remains stable while there's contention.
+Atomic::inc_ptr(&_count);
+{ // Change java thread status to indicate blocked on monitor enter.
+JavaThreadBlockedOnMonitorEnterState jtbmes(jt, this);
+DTRACE_MONITOR_PROBE(contended__enter, this, object(), jt);
+if (JvmtiExport::should_post_monitor_contended_enter()) {
+JvmtiExport::post_monitor_contended_enter(jt, this);
+}
+OSThreadContendState osts(Self->osthread());
+ThreadBlockInVM tbivm(jt);
+Self->set_current_pending_monitor(this);
+// TODO-FIXME: change the following for(;;) loop to straight-line code.
+for (;;) {
+jt->set_suspend_equivalent();
+// cleared by handle_special_suspend_equivalent_condition()
+// or java_suspend_self()
+EnterI (THREAD) ;
+if (!ExitSuspendEquivalent(jt)) break ;
+//
+// We have acquired the contended monitor, but while we were
+// waiting another thread suspended us. We don't want to enter
+// the monitor while suspended because that would surprise the
+// thread that suspended us.
+//
+_recursions = 0 ;
+_succ = NULL ;
+exit (Self) ;
+jt->java_suspend_self();
+}
+Self->set_current_pending_monitor(NULL);
+}
+Atomic::dec_ptr(&_count);
+assert (_count >= 0, "invariant") ;
+Self->_Stalled = 0 ;
+// Must either set _recursions = 0 or ASSERT _recursions == 0.
+assert (_recursions == 0     , "invariant") ;
+assert (_owner == Self       , "invariant") ;
+assert (_succ  != Self       , "invariant") ;
+assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
+// The thread -- now the owner -- is back in vm mode.
+// Report the glorious news via TI,DTrace and jvmstat.
+// The probe effect is non-trivial.  All the reportage occurs
+// while we hold the monitor, increasing the length of the critical
+// section.  Amdahl's parallel speedup law comes vividly into play.
+//
+// Another option might be to aggregate the events (thread local or
+// per-monitor aggregation) and defer reporting until a more opportune
+// time -- such as next time some thread encounters contention but has
+// yet to acquire the lock.  While spinning that thread could
+// spinning we could increment JVMStat counters, etc.
+DTRACE_MONITOR_PROBE(contended__entered, this, object(), jt);
+if (JvmtiExport::should_post_monitor_contended_entered()) {
+JvmtiExport::post_monitor_contended_entered(jt, this);
+}
+if (ObjectMonitor::_sync_ContendedLockAttempts != NULL) {
+ObjectMonitor::_sync_ContendedLockAttempts->inc() ;
+}
+}
+// Caveat: TryLock() is not necessarily serializing if it returns failure.
+// Callers must compensate as needed.
+int ObjectMonitor::TryLock (Thread * Self) {
+for (;;) {
+void * own = _owner ;
+if (own != NULL) return 0 ;
+if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
+// Either guarantee _recursions == 0 or set _recursions = 0.
+assert (_recursions == 0, "invariant") ;
+assert (_owner == Self, "invariant") ;
+// CONSIDER: set or assert that OwnerIsThread == 1
+return 1 ;
+}
+// The lock had been free momentarily, but we lost the race to the lock.
+// Interference -- the CAS failed.
+// We can either return -1 or retry.
+// Retry doesn't make as much sense because the lock was just acquired.
+if (true) return -1 ;
+}
+}
+void ATTR ObjectMonitor::EnterI (TRAPS) {
+Thread * Self = THREAD ;
+assert (Self->is_Java_thread(), "invariant") ;
+assert (((JavaThread *) Self)->thread_state() == _thread_blocked   , "invariant") ;
+// Try the lock - TATAS
+if (TryLock (Self) > 0) {
+assert (_succ != Self              , "invariant") ;
+assert (_owner == Self             , "invariant") ;
+assert (_Responsible != Self       , "invariant") ;
+return ;
+}
+DeferredInitialize () ;
+// We try one round of spinning *before* enqueueing Self.
+//
+// If the _owner is ready but OFFPROC we could use a YieldTo()
+// operation to donate the remainder of this thread's quantum
+// to the owner.  This has subtle but beneficial affinity
+// effects.
+if (TrySpin (Self) > 0) {
+assert (_owner == Self        , "invariant") ;
+assert (_succ != Self         , "invariant") ;
+assert (_Responsible != Self  , "invariant") ;
+return ;
+}
+// The Spin failed -- Enqueue and park the thread ...
+assert (_succ  != Self            , "invariant") ;
+assert (_owner != Self            , "invariant") ;
+assert (_Responsible != Self      , "invariant") ;
+// Enqueue "Self" on ObjectMonitor's _cxq.
+//
+// Node acts as a proxy for Self.
+// As an aside, if were to ever rewrite the synchronization code mostly
+// in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
+// Java objects.  This would avoid awkward lifecycle and liveness issues,
+// as well as eliminate a subset of ABA issues.
+// TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
+//
+ObjectWaiter node(Self) ;
+Self->_ParkEvent->reset() ;
+node._prev   = (ObjectWaiter *) 0xBAD ;
+node.TState  = ObjectWaiter::TS_CXQ ;
+// Push "Self" onto the front of the _cxq.
+// Once on cxq/EntryList, Self stays on-queue until it acquires the lock.
+// Note that spinning tends to reduce the rate at which threads
+// enqueue and dequeue on EntryList|cxq.
+ObjectWaiter * nxt ;
+for (;;) {
+node._next = nxt = _cxq ;
+if (Atomic::cmpxchg_ptr (&node, &_cxq, nxt) == nxt) break ;
+// Interference - the CAS failed because _cxq changed.  Just retry.
+// As an optional optimization we retry the lock.
+if (TryLock (Self) > 0) {
+assert (_succ != Self         , "invariant") ;
+assert (_owner == Self        , "invariant") ;
+assert (_Responsible != Self  , "invariant") ;
+return ;
+}
+}
+// Check for cxq|EntryList edge transition to non-null.  This indicates
+// the onset of contention.  While contention persists exiting threads
+// will use a ST:MEMBAR:LD 1-1 exit protocol.  When contention abates exit
+// operations revert to the faster 1-0 mode.  This enter operation may interleave
+// (race) a concurrent 1-0 exit operation, resulting in stranding, so we
+// arrange for one of the contending thread to use a timed park() operations
+// to detect and recover from the race.  (Stranding is form of progress failure
+// where the monitor is unlocked but all the contending threads remain parked).
+// That is, at least one of the contended threads will periodically poll _owner.
+// One of the contending threads will become the designated "Responsible" thread.
+// The Responsible thread uses a timed park instead of a normal indefinite park
+// operation -- it periodically wakes and checks for and recovers from potential
+// strandings admitted by 1-0 exit operations.   We need at most one Responsible
+// thread per-monitor at any given moment.  Only threads on cxq|EntryList may
+// be responsible for a monitor.
+//
+// Currently, one of the contended threads takes on the added role of "Responsible".
+// A viable alternative would be to use a dedicated "stranding checker" thread
+// that periodically iterated over all the threads (or active monitors) and unparked
+// successors where there was risk of stranding.  This would help eliminate the
+// timer scalability issues we see on some platforms as we'd only have one thread
+// -- the checker -- parked on a timer.
+if ((SyncFlags & 16) == 0 && nxt == NULL && _EntryList == NULL) {
+// Try to assume the role of responsible thread for the monitor.
+// CONSIDER:  ST vs CAS vs { if (Responsible==null) Responsible=Self }
+Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
+}
+// The lock have been released while this thread was occupied queueing
+// itself onto _cxq.  To close the race and avoid "stranding" and
+// progress-liveness failure we must resample-retry _owner before parking.
+// Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
+// In this case the ST-MEMBAR is accomplished with CAS().
+//
+// TODO: Defer all thread state transitions until park-time.
+// Since state transitions are heavy and inefficient we'd like
+// to defer the state transitions until absolutely necessary,
+// and in doing so avoid some transitions ...
+TEVENT (Inflated enter - Contention) ;
+int nWakeups = 0 ;
+int RecheckInterval = 1 ;
+for (;;) {
+if (TryLock (Self) > 0) break ;
+assert (_owner != Self, "invariant") ;
+if ((SyncFlags & 2) && _Responsible == NULL) {
+Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
+}
+// park self
+if (_Responsible == Self || (SyncFlags & 1)) {
+TEVENT (Inflated enter - park TIMED) ;
+Self->_ParkEvent->park ((jlong) RecheckInterval) ;
+// Increase the RecheckInterval, but clamp the value.
+RecheckInterval *= 8 ;
+if (RecheckInterval > 1000) RecheckInterval = 1000 ;
+} else {
+TEVENT (Inflated enter - park UNTIMED) ;
+Self->_ParkEvent->park() ;
+}
+if (TryLock(Self) > 0) break ;
+// The lock is still contested.
+// Keep a tally of the # of futile wakeups.
+// Note that the counter is not protected by a lock or updated by atomics.
+// That is by design - we trade "lossy" counters which are exposed to
+// races during updates for a lower probe effect.
+TEVENT (Inflated enter - Futile wakeup) ;
+if (ObjectMonitor::_sync_FutileWakeups != NULL) {
+ObjectMonitor::_sync_FutileWakeups->inc() ;
+}
+++ nWakeups ;
+// Assuming this is not a spurious wakeup we'll normally find _succ == Self.
+// We can defer clearing _succ until after the spin completes
+// TrySpin() must tolerate being called with _succ == Self.
+// Try yet another round of adaptive spinning.
+if ((Knob_SpinAfterFutile & 1) && TrySpin (Self) > 0) break ;
+// We can find that we were unpark()ed and redesignated _succ while
+// we were spinning.  That's harmless.  If we iterate and call park(),
+// park() will consume the event and return immediately and we'll
+// just spin again.  This pattern can repeat, leaving _succ to simply
+// spin on a CPU.  Enable Knob_ResetEvent to clear pending unparks().
+// Alternately, we can sample fired() here, and if set, forgo spinning
+// in the next iteration.
+if ((Knob_ResetEvent & 1) && Self->_ParkEvent->fired()) {
+Self->_ParkEvent->reset() ;
+OrderAccess::fence() ;
+}
+if (_succ == Self) _succ = NULL ;
+// Invariant: after clearing _succ a thread *must* retry _owner before parking.
+OrderAccess::fence() ;
+}
+// Egress :
+// Self has acquired the lock -- Unlink Self from the cxq or EntryList.
+// Normally we'll find Self on the EntryList .
+// From the perspective of the lock owner (this thread), the
+// EntryList is stable and cxq is prepend-only.
+// The head of cxq is volatile but the interior is stable.
+// In addition, Self.TState is stable.
+assert (_owner == Self      , "invariant") ;
+assert (object() != NULL    , "invariant") ;
+// I'd like to write:
+//   guarantee (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
+// but as we're at a safepoint that's not safe.
+UnlinkAfterAcquire (Self, &node) ;
+if (_succ == Self) _succ = NULL ;
+assert (_succ != Self, "invariant") ;
+if (_Responsible == Self) {
+_Responsible = NULL ;
+// Dekker pivot-point.
+// Consider OrderAccess::storeload() here
+// We may leave threads on cxq|EntryList without a designated
+// "Responsible" thread.  This is benign.  When this thread subsequently
+// exits the monitor it can "see" such preexisting "old" threads --
+// threads that arrived on the cxq|EntryList before the fence, above --
+// by LDing cxq|EntryList.  Newly arrived threads -- that is, threads
+// that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
+// non-null and elect a new "Responsible" timer thread.
+//
+// This thread executes:
+//    ST Responsible=null; MEMBAR    (in enter epilog - here)
+//    LD cxq|EntryList               (in subsequent exit)
+//
+// Entering threads in the slow/contended path execute:
+//    ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
+//    The (ST cxq; MEMBAR) is accomplished with CAS().
+//
+// The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
+// exit operation from floating above the ST Responsible=null.
+//
+// In *practice* however, EnterI() is always followed by some atomic
+// operation such as the decrement of _count in ::enter().  Those atomics
+// obviate the need for the explicit MEMBAR, above.
+}
+// We've acquired ownership with CAS().
+// CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
+// But since the CAS() this thread may have also stored into _succ,
+// EntryList, cxq or Responsible.  These meta-data updates must be
+// visible __before this thread subsequently drops the lock.
+// Consider what could occur if we didn't enforce this constraint --
+// STs to monitor meta-data and user-data could reorder with (become
+// visible after) the ST in exit that drops ownership of the lock.
+// Some other thread could then acquire the lock, but observe inconsistent
+// or old monitor meta-data and heap data.  That violates the JMM.
+// To that end, the 1-0 exit() operation must have at least STST|LDST
+// "release" barrier semantics.  Specifically, there must be at least a
+// STST|LDST barrier in exit() before the ST of null into _owner that drops
+// the lock.   The barrier ensures that changes to monitor meta-data and data
+// protected by the lock will be visible before we release the lock, and
+// therefore before some other thread (CPU) has a chance to acquire the lock.
+// See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
+//
+// Critically, any prior STs to _succ or EntryList must be visible before
+// the ST of null into _owner in the *subsequent* (following) corresponding
+// monitorexit.  Recall too, that in 1-0 mode monitorexit does not necessarily
+// execute a serializing instruction.
+if (SyncFlags & 8) {
+OrderAccess::fence() ;
+}
+return ;
+}
+// ReenterI() is a specialized inline form of the latter half of the
+// contended slow-path from EnterI().  We use ReenterI() only for
+// monitor reentry in wait().
+//
+// In the future we should reconcile EnterI() and ReenterI(), adding
+// Knob_Reset and Knob_SpinAfterFutile support and restructuring the
+// loop accordingly.
+void ATTR ObjectMonitor::ReenterI (Thread * Self, ObjectWaiter * SelfNode) {
+assert (Self != NULL                , "invariant") ;
+assert (SelfNode != NULL            , "invariant") ;
+assert (SelfNode->_thread == Self   , "invariant") ;
+assert (_waiters > 0                , "invariant") ;
+assert (((oop)(object()))->mark() == markOopDesc::encode(this) , "invariant") ;
+assert (((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
+JavaThread * jt = (JavaThread *) Self ;
+int nWakeups = 0 ;
+for (;;) {
+ObjectWaiter::TStates v = SelfNode->TState ;
+guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
+assert    (_owner != Self, "invariant") ;
+if (TryLock (Self) > 0) break ;
+if (TrySpin (Self) > 0) break ;
+TEVENT (Wait Reentry - parking) ;
+// State transition wrappers around park() ...
+// ReenterI() wisely defers state transitions until
+// it's clear we must park the thread.
+{
+OSThreadContendState osts(Self->osthread());
+ThreadBlockInVM tbivm(jt);
+// cleared by handle_special_suspend_equivalent_condition()
+// or java_suspend_self()
+jt->set_suspend_equivalent();
+if (SyncFlags & 1) {
+Self->_ParkEvent->park ((jlong)1000) ;
+} else {
+Self->_ParkEvent->park () ;
+}
+// were we externally suspended while we were waiting?
+for (;;) {
+if (!ExitSuspendEquivalent (jt)) break ;
+if (_succ == Self) { _succ = NULL; OrderAccess::fence(); }
+jt->java_suspend_self();
+jt->set_suspend_equivalent();
+}
+}
+// Try again, but just so we distinguish between futile wakeups and
+// successful wakeups.  The following test isn't algorithmically
+// necessary, but it helps us maintain sensible statistics.
+if (TryLock(Self) > 0) break ;
+// The lock is still contested.
+// Keep a tally of the # of futile wakeups.
+// Note that the counter is not protected by a lock or updated by atomics.
+// That is by design - we trade "lossy" counters which are exposed to
+// races during updates for a lower probe effect.
+TEVENT (Wait Reentry - futile wakeup) ;
+++ nWakeups ;
+// Assuming this is not a spurious wakeup we'll normally
+// find that _succ == Self.
+if (_succ == Self) _succ = NULL ;
+// Invariant: after clearing _succ a contending thread
+// *must* retry  _owner before parking.
+OrderAccess::fence() ;
+if (ObjectMonitor::_sync_FutileWakeups != NULL) {
+ObjectMonitor::_sync_FutileWakeups->inc() ;
+}
+}
+// Self has acquired the lock -- Unlink Self from the cxq or EntryList .
+// Normally we'll find Self on the EntryList.
+// Unlinking from the EntryList is constant-time and atomic-free.
+// From the perspective of the lock owner (this thread), the
+// EntryList is stable and cxq is prepend-only.
+// The head of cxq is volatile but the interior is stable.
+// In addition, Self.TState is stable.
+assert (_owner == Self, "invariant") ;
+assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
+UnlinkAfterAcquire (Self, SelfNode) ;
+if (_succ == Self) _succ = NULL ;
+assert (_succ != Self, "invariant") ;
+SelfNode->TState = ObjectWaiter::TS_RUN ;
+OrderAccess::fence() ;      // see comments at the end of EnterI()
+}
+// after the thread acquires the lock in ::enter().  Equally, we could defer
+// unlinking the thread until ::exit()-time.
+void ObjectMonitor::UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode)
+{
+assert (_owner == Self, "invariant") ;
+assert (SelfNode->_thread == Self, "invariant") ;
+if (SelfNode->TState == ObjectWaiter::TS_ENTER) {
+// Normal case: remove Self from the DLL EntryList .
+// This is a constant-time operation.
+ObjectWaiter * nxt = SelfNode->_next ;
+ObjectWaiter * prv = SelfNode->_prev ;
+if (nxt != NULL) nxt->_prev = prv ;
+if (prv != NULL) prv->_next = nxt ;
+if (SelfNode == _EntryList ) _EntryList = nxt ;
+assert (nxt == NULL || nxt->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+assert (prv == NULL || prv->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+TEVENT (Unlink from EntryList) ;
+} else {
+guarantee (SelfNode->TState == ObjectWaiter::TS_CXQ, "invariant") ;
+// Inopportune interleaving -- Self is still on the cxq.
+// This usually means the enqueue of self raced an exiting thread.
+// Normally we'll find Self near the front of the cxq, so
+// dequeueing is typically fast.  If needbe we can accelerate
+// this with some MCS/CHL-like bidirectional list hints and advisory
+// back-links so dequeueing from the interior will normally operate
+// in constant-time.
+// Dequeue Self from either the head (with CAS) or from the interior
+// with a linear-time scan and normal non-atomic memory operations.
+// CONSIDER: if Self is on the cxq then simply drain cxq into EntryList
+// and then unlink Self from EntryList.  We have to drain eventually,
+// so it might as well be now.
+ObjectWaiter * v = _cxq ;
+assert (v != NULL, "invariant") ;
+if (v != SelfNode || Atomic::cmpxchg_ptr (SelfNode->_next, &_cxq, v) != v) {
+// The CAS above can fail from interference IFF a "RAT" arrived.
+// In that case Self must be in the interior and can no longer be
+// at the head of cxq.
+if (v == SelfNode) {
+assert (_cxq != v, "invariant") ;
+v = _cxq ;          // CAS above failed - start scan at head of list
+}
+ObjectWaiter * p ;
+ObjectWaiter * q = NULL ;
+for (p = v ; p != NULL && p != SelfNode; p = p->_next) {
+q = p ;
+assert (p->TState == ObjectWaiter::TS_CXQ, "invariant") ;
+}
+assert (v != SelfNode,  "invariant") ;
+assert (p == SelfNode,  "Node not found on cxq") ;
+assert (p != _cxq,      "invariant") ;
+assert (q != NULL,      "invariant") ;
+assert (q->_next == p,  "invariant") ;
+q->_next = p->_next ;
+}
+TEVENT (Unlink from cxq) ;
+}
+// Diagnostic hygiene ...
+SelfNode->_prev  = (ObjectWaiter *) 0xBAD ;
+SelfNode->_next  = (ObjectWaiter *) 0xBAD ;
+SelfNode->TState = ObjectWaiter::TS_RUN ;
+}
+// -----------------------------------------------------------------------------
+// Exit support
+//
+// exit()
+// ~~~~~~
+// Note that the collector can't reclaim the objectMonitor or deflate
+// the object out from underneath the thread calling ::exit() as the
+// thread calling ::exit() never transitions to a stable state.
+// This inhibits GC, which in turn inhibits asynchronous (and
+// inopportune) reclamation of "this".
+//
+// We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
+// There's one exception to the claim above, however.  EnterI() can call
+// exit() to drop a lock if the acquirer has been externally suspended.
+// In that case exit() is called with _thread_state as _thread_blocked,
+// but the monitor's _count field is > 0, which inhibits reclamation.
+//
+// 1-0 exit
+// ~~~~~~~~
+// ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
+// the fast-path operators have been optimized so the common ::exit()
+// operation is 1-0.  See i486.ad fast_unlock(), for instance.
+// The code emitted by fast_unlock() elides the usual MEMBAR.  This
+// greatly improves latency -- MEMBAR and CAS having considerable local
+// latency on modern processors -- but at the cost of "stranding".  Absent the
+// MEMBAR, a thread in fast_unlock() can race a thread in the slow
+// ::enter() path, resulting in the entering thread being stranding
+// and a progress-liveness failure.   Stranding is extremely rare.
+// We use timers (timed park operations) & periodic polling to detect
+// and recover from stranding.  Potentially stranded threads periodically
+// wake up and poll the lock.  See the usage of the _Responsible variable.
+//
+// The CAS() in enter provides for safety and exclusion, while the CAS or
+// MEMBAR in exit provides for progress and avoids stranding.  1-0 locking
+// eliminates the CAS/MEMBAR from the exist path, but it admits stranding.
+// We detect and recover from stranding with timers.
+//
+// If a thread transiently strands it'll park until (a) another
+// thread acquires the lock and then drops the lock, at which time the
+// exiting thread will notice and unpark the stranded thread, or, (b)
+// the timer expires.  If the lock is high traffic then the stranding latency
+// will be low due to (a).  If the lock is low traffic then the odds of
+// stranding are lower, although the worst-case stranding latency
+// is longer.  Critically, we don't want to put excessive load in the
+// platform's timer subsystem.  We want to minimize both the timer injection
+// rate (timers created/sec) as well as the number of timers active at
+// any one time.  (more precisely, we want to minimize timer-seconds, which is
+// the integral of the # of active timers at any instant over time).
+// Both impinge on OS scalability.  Given that, at most one thread parked on
+// a monitor will use a timer.
+void ATTR ObjectMonitor::exit(TRAPS) {
+Thread * Self = THREAD ;
+if (THREAD != _owner) {
+if (THREAD->is_lock_owned((address) _owner)) {
+// Transmute _owner from a BasicLock pointer to a Thread address.
+// We don't need to hold _mutex for this transition.
+// Non-null to Non-null is safe as long as all readers can
+// tolerate either flavor.
+assert (_recursions == 0, "invariant") ;
+_owner = THREAD ;
+_recursions = 0 ;
+OwnerIsThread = 1 ;
+} else {
+// NOTE: we need to handle unbalanced monitor enter/exit
+// in native code by throwing an exception.
+// TODO: Throw an IllegalMonitorStateException ?
+TEVENT (Exit - Throw IMSX) ;
+assert(false, "Non-balanced monitor enter/exit!");
+if (false) {
+THROW(vmSymbols::java_lang_IllegalMonitorStateException());
+}
+return;
+}
+}
+if (_recursions != 0) {
+_recursions--;        // this is simple recursive enter
+TEVENT (Inflated exit - recursive) ;
+return ;
+}
+// Invariant: after setting Responsible=null an thread must execute
+// a MEMBAR or other serializing instruction before fetching EntryList|cxq.
+if ((SyncFlags & 4) == 0) {
+_Responsible = NULL ;
+}
+for (;;) {
+assert (THREAD == _owner, "invariant") ;
+if (Knob_ExitPolicy == 0) {
+// release semantics: prior loads and stores from within the critical section
+// must not float (reorder) past the following store that drops the lock.
+// On SPARC that requires MEMBAR #loadstore|#storestore.
+// But of course in TSO #loadstore|#storestore is not required.
+// I'd like to write one of the following:
+// A.  OrderAccess::release() ; _owner = NULL
+// B.  OrderAccess::loadstore(); OrderAccess::storestore(); _owner = NULL;
+// Unfortunately OrderAccess::release() and OrderAccess::loadstore() both
+// store into a _dummy variable.  That store is not needed, but can result
+// in massive wasteful coherency traffic on classic SMP systems.
+// Instead, I use release_store(), which is implemented as just a simple
+// ST on x64, x86 and SPARC.
+OrderAccess::release_store_ptr (&_owner, NULL) ;   // drop the lock
+OrderAccess::storeload() ;                         // See if we need to wake a successor
+if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
+TEVENT (Inflated exit - simple egress) ;
+return ;
+}
+TEVENT (Inflated exit - complex egress) ;
+// Normally the exiting thread is responsible for ensuring succession,
+// but if other successors are ready or other entering threads are spinning
+// then this thread can simply store NULL into _owner and exit without
+// waking a successor.  The existence of spinners or ready successors
+// guarantees proper succession (liveness).  Responsibility passes to the
+// ready or running successors.  The exiting thread delegates the duty.
+// More precisely, if a successor already exists this thread is absolved
+// of the responsibility of waking (unparking) one.
+//
+// The _succ variable is critical to reducing futile wakeup frequency.
+// _succ identifies the "heir presumptive" thread that has been made
+// ready (unparked) but that has not yet run.  We need only one such
+// successor thread to guarantee progress.
+// See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
+// section 3.3 "Futile Wakeup Throttling" for details.
+//
+// Note that spinners in Enter() also set _succ non-null.
+// In the current implementation spinners opportunistically set
+// _succ so that exiting threads might avoid waking a successor.
+// Another less appealing alternative would be for the exiting thread
+// to drop the lock and then spin briefly to see if a spinner managed
+// to acquire the lock.  If so, the exiting thread could exit
+// immediately without waking a successor, otherwise the exiting
+// thread would need to dequeue and wake a successor.
+// (Note that we'd need to make the post-drop spin short, but no
+// shorter than the worst-case round-trip cache-line migration time.
+// The dropped lock needs to become visible to the spinner, and then
+// the acquisition of the lock by the spinner must become visible to
+// the exiting thread).
+//
+// It appears that an heir-presumptive (successor) must be made ready.
+// Only the current lock owner can manipulate the EntryList or
+// drain _cxq, so we need to reacquire the lock.  If we fail
+// to reacquire the lock the responsibility for ensuring succession
+// falls to the new owner.
+//
+if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
+return ;
+}
+TEVENT (Exit - Reacquired) ;
+} else {
+if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
+OrderAccess::release_store_ptr (&_owner, NULL) ;   // drop the lock
+OrderAccess::storeload() ;
+// Ratify the previously observed values.
+if (_cxq == NULL || _succ != NULL) {
+TEVENT (Inflated exit - simple egress) ;
+return ;
+}
+// inopportune interleaving -- the exiting thread (this thread)
+// in the fast-exit path raced an entering thread in the slow-enter
+// path.
+// We have two choices:
+// A.  Try to reacquire the lock.
+//     If the CAS() fails return immediately, otherwise
+//     we either restart/rerun the exit operation, or simply
+//     fall-through into the code below which wakes a successor.
+// B.  If the elements forming the EntryList|cxq are TSM
+//     we could simply unpark() the lead thread and return
+//     without having set _succ.
+if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
+TEVENT (Inflated exit - reacquired succeeded) ;
+return ;
+}
+TEVENT (Inflated exit - reacquired failed) ;
+} else {
+TEVENT (Inflated exit - complex egress) ;
+}
+}
+guarantee (_owner == THREAD, "invariant") ;
+ObjectWaiter * w = NULL ;
+int QMode = Knob_QMode ;
+if (QMode == 2 && _cxq != NULL) {
+// QMode == 2 : cxq has precedence over EntryList.
+// Try to directly wake a successor from the cxq.
+// If successful, the successor will need to unlink itself from cxq.
+w = _cxq ;
+assert (w != NULL, "invariant") ;
+assert (w->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
+ExitEpilog (Self, w) ;
+return ;
+}
+if (QMode == 3 && _cxq != NULL) {
+// Aggressively drain cxq into EntryList at the first opportunity.
+// This policy ensure that recently-run threads live at the head of EntryList.
+// Drain _cxq into EntryList - bulk transfer.
+// First, detach _cxq.
+// The following loop is tantamount to: w = swap (&cxq, NULL)
+w = _cxq ;
+for (;;) {
+assert (w != NULL, "Invariant") ;
+ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
+if (u == w) break ;
+w = u ;
+}
+assert (w != NULL              , "invariant") ;
+ObjectWaiter * q = NULL ;
+ObjectWaiter * p ;
+for (p = w ; p != NULL ; p = p->_next) {
+guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
+p->TState = ObjectWaiter::TS_ENTER ;
+p->_prev = q ;
+q = p ;
+}
+// Append the RATs to the EntryList
+// TODO: organize EntryList as a CDLL so we can locate the tail in constant-time.
+ObjectWaiter * Tail ;
+for (Tail = _EntryList ; Tail != NULL && Tail->_next != NULL ; Tail = Tail->_next) ;
+if (Tail == NULL) {
+_EntryList = w ;
+} else {
+Tail->_next = w ;
+w->_prev = Tail ;
+}
+// Fall thru into code that tries to wake a successor from EntryList
+}
+if (QMode == 4 && _cxq != NULL) {
+// Aggressively drain cxq into EntryList at the first opportunity.
+// This policy ensure that recently-run threads live at the head of EntryList.
+// Drain _cxq into EntryList - bulk transfer.
+// First, detach _cxq.
+// The following loop is tantamount to: w = swap (&cxq, NULL)
+w = _cxq ;
+for (;;) {
+assert (w != NULL, "Invariant") ;
+ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
+if (u == w) break ;
+w = u ;
+}
+assert (w != NULL              , "invariant") ;
+ObjectWaiter * q = NULL ;
+ObjectWaiter * p ;
+for (p = w ; p != NULL ; p = p->_next) {
+guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
+p->TState = ObjectWaiter::TS_ENTER ;
+p->_prev = q ;
+q = p ;
+}
+// Prepend the RATs to the EntryList
+if (_EntryList != NULL) {
+q->_next = _EntryList ;
+_EntryList->_prev = q ;
+}
+_EntryList = w ;
+// Fall thru into code that tries to wake a successor from EntryList
+}
+w = _EntryList  ;
+if (w != NULL) {
+// I'd like to write: guarantee (w->_thread != Self).
+// But in practice an exiting thread may find itself on the EntryList.
+// Lets say thread T1 calls O.wait().  Wait() enqueues T1 on O's waitset and
+// then calls exit().  Exit release the lock by setting O._owner to NULL.
+// Lets say T1 then stalls.  T2 acquires O and calls O.notify().  The
+// notify() operation moves T1 from O's waitset to O's EntryList. T2 then
+// release the lock "O".  T2 resumes immediately after the ST of null into
+// _owner, above.  T2 notices that the EntryList is populated, so it
+// reacquires the lock and then finds itself on the EntryList.
+// Given all that, we have to tolerate the circumstance where "w" is
+// associated with Self.
+assert (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+ExitEpilog (Self, w) ;
+return ;
+}
+// If we find that both _cxq and EntryList are null then just
+// re-run the exit protocol from the top.
+w = _cxq ;
+if (w == NULL) continue ;
+// Drain _cxq into EntryList - bulk transfer.
+// First, detach _cxq.
+// The following loop is tantamount to: w = swap (&cxq, NULL)
+for (;;) {
+assert (w != NULL, "Invariant") ;
+ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
+if (u == w) break ;
+w = u ;
+}
+TEVENT (Inflated exit - drain cxq into EntryList) ;
+assert (w != NULL              , "invariant") ;
+assert (_EntryList  == NULL    , "invariant") ;
+// Convert the LIFO SLL anchored by _cxq into a DLL.
+// The list reorganization step operates in O(LENGTH(w)) time.
+// It's critical that this step operate quickly as
+// "Self" still holds the outer-lock, restricting parallelism
+// and effectively lengthening the critical section.
+// Invariant: s chases t chases u.
+// TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
+// we have faster access to the tail.
+if (QMode == 1) {
+// QMode == 1 : drain cxq to EntryList, reversing order
+// We also reverse the order of the list.
+ObjectWaiter * s = NULL ;
+ObjectWaiter * t = w ;
+ObjectWaiter * u = NULL ;
+while (t != NULL) {
+guarantee (t->TState == ObjectWaiter::TS_CXQ, "invariant") ;
+t->TState = ObjectWaiter::TS_ENTER ;
+u = t->_next ;
+t->_prev = u ;
+t->_next = s ;
+s = t;
+t = u ;
+}
+_EntryList  = s ;
+assert (s != NULL, "invariant") ;
+} else {
+// QMode == 0 or QMode == 2
+_EntryList = w ;
+ObjectWaiter * q = NULL ;
+ObjectWaiter * p ;
+for (p = w ; p != NULL ; p = p->_next) {
+guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
+p->TState = ObjectWaiter::TS_ENTER ;
+p->_prev = q ;
+q = p ;
+}
+}
+// In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = NULL
+// The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
+// See if we can abdicate to a spinner instead of waking a thread.
+// A primary goal of the implementation is to reduce the
+// context-switch rate.
+if (_succ != NULL) continue;
+w = _EntryList  ;
+if (w != NULL) {
+guarantee (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+ExitEpilog (Self, w) ;
+return ;
+}
+}
+}
+// ExitSuspendEquivalent:
+// A faster alternate to handle_special_suspend_equivalent_condition()
+//
+// handle_special_suspend_equivalent_condition() unconditionally
+// acquires the SR_lock.  On some platforms uncontended MutexLocker()
+// operations have high latency.  Note that in ::enter() we call HSSEC
+// while holding the monitor, so we effectively lengthen the critical sections.
+//
+// There are a number of possible solutions:
+//
+// A.  To ameliorate the problem we might also defer state transitions
+//     to as late as possible -- just prior to parking.
+//     Given that, we'd call HSSEC after having returned from park(),
+//     but before attempting to acquire the monitor.  This is only a
+//     partial solution.  It avoids calling HSSEC while holding the
+//     monitor (good), but it still increases successor reacquisition latency --
+//     the interval between unparking a successor and the time the successor
+//     resumes and retries the lock.  See ReenterI(), which defers state transitions.
+//     If we use this technique we can also avoid EnterI()-exit() loop
+//     in ::enter() where we iteratively drop the lock and then attempt
+//     to reacquire it after suspending.
+//
+// B.  In the future we might fold all the suspend bits into a
+//     composite per-thread suspend flag and then update it with CAS().
+//     Alternately, a Dekker-like mechanism with multiple variables
+//     would suffice:
+//       ST Self->_suspend_equivalent = false
+//       MEMBAR
+//       LD Self_>_suspend_flags
+//
+bool ObjectMonitor::ExitSuspendEquivalent (JavaThread * jSelf) {
+int Mode = Knob_FastHSSEC ;
+if (Mode && !jSelf->is_external_suspend()) {
+assert (jSelf->is_suspend_equivalent(), "invariant") ;
+jSelf->clear_suspend_equivalent() ;
+if (2 == Mode) OrderAccess::storeload() ;
+if (!jSelf->is_external_suspend()) return false ;
+// We raced a suspension -- fall thru into the slow path
+TEVENT (ExitSuspendEquivalent - raced) ;
+jSelf->set_suspend_equivalent() ;
+}
+return jSelf->handle_special_suspend_equivalent_condition() ;
+}
+void ObjectMonitor::ExitEpilog (Thread * Self, ObjectWaiter * Wakee) {
+assert (_owner == Self, "invariant") ;
+// Exit protocol:
+// 1. ST _succ = wakee
+// 2. membar #loadstore|#storestore;
+// 2. ST _owner = NULL
+// 3. unpark(wakee)
+_succ = Knob_SuccEnabled ? Wakee->_thread : NULL ;
+ParkEvent * Trigger = Wakee->_event ;
+// Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
+// The thread associated with Wakee may have grabbed the lock and "Wakee" may be
+// out-of-scope (non-extant).
+Wakee  = NULL ;
+// Drop the lock
+OrderAccess::release_store_ptr (&_owner, NULL) ;
+OrderAccess::fence() ;                               // ST _owner vs LD in unpark()
+if (SafepointSynchronize::do_call_back()) {
+TEVENT (unpark before SAFEPOINT) ;
+}
+DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
+Trigger->unpark() ;
+// Maintain stats and report events to JVMTI
+if (ObjectMonitor::_sync_Parks != NULL) {
+ObjectMonitor::_sync_Parks->inc() ;
+}
+}
+// -----------------------------------------------------------------------------
+// Class Loader deadlock handling.
+//
+// complete_exit exits a lock returning recursion count
+// complete_exit/reenter operate as a wait without waiting
+// complete_exit requires an inflated monitor
+// The _owner field is not always the Thread addr even with an
+// inflated monitor, e.g. the monitor can be inflated by a non-owning
+// thread due to contention.
+intptr_t ObjectMonitor::complete_exit(TRAPS) {
+Thread * const Self = THREAD;
+assert(Self->is_Java_thread(), "Must be Java thread!");
+JavaThread *jt = (JavaThread *)THREAD;
+DeferredInitialize();
+if (THREAD != _owner) {
+if (THREAD->is_lock_owned ((address)_owner)) {
+assert(_recursions == 0, "internal state error");
+_owner = THREAD ;   /* Convert from basiclock addr to Thread addr */
+_recursions = 0 ;
+OwnerIsThread = 1 ;
+}
+}
+guarantee(Self == _owner, "complete_exit not owner");
+intptr_t save = _recursions; // record the old recursion count
+_recursions = 0;        // set the recursion level to be 0
+exit (Self) ;           // exit the monitor
+guarantee (_owner != Self, "invariant");
+return save;
+}
+// reenter() enters a lock and sets recursion count
+// complete_exit/reenter operate as a wait without waiting
+void ObjectMonitor::reenter(intptr_t recursions, TRAPS) {
+Thread * const Self = THREAD;
+assert(Self->is_Java_thread(), "Must be Java thread!");
+JavaThread *jt = (JavaThread *)THREAD;
+guarantee(_owner != Self, "reenter already owner");
+enter (THREAD);       // enter the monitor
+guarantee (_recursions == 0, "reenter recursion");
+_recursions = recursions;
+return;
+}
+// -----------------------------------------------------------------------------
+// A macro is used below because there may already be a pending
+// exception which should not abort the execution of the routines
+// which use this (which is why we don't put this into check_slow and
+// call it with a CHECK argument).
+#define CHECK_OWNER()                                                             \
+do {                                                                            \
+if (THREAD != _owner) {                                                       \
+if (THREAD->is_lock_owned((address) _owner)) {                              \
+_owner = THREAD ;  /* Convert from basiclock addr to Thread addr */       \
+_recursions = 0;                                                          \
+OwnerIsThread = 1 ;                                                       \
+} else {                                                                    \
+TEVENT (Throw IMSX) ;                                                     \
+THROW(vmSymbols::java_lang_IllegalMonitorStateException());               \
+}                                                                           \
+}                                                                             \
+} while (false)
+// check_slow() is a misnomer.  It's called to simply to throw an IMSX exception.
+// TODO-FIXME: remove check_slow() -- it's likely dead.
+void ObjectMonitor::check_slow(TRAPS) {
+TEVENT (check_slow - throw IMSX) ;
+assert(THREAD != _owner && !THREAD->is_lock_owned((address) _owner), "must not be owner");
+THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), "current thread not owner");
+}
+static int Adjust (volatile int * adr, int dx) {
+int v ;
+for (v = *adr ; Atomic::cmpxchg (v + dx, adr, v) != v; v = *adr) ;
+return v ;
+}
+// -----------------------------------------------------------------------------
+// Wait/Notify/NotifyAll
+//
+// Note: a subset of changes to ObjectMonitor::wait()
+// will need to be replicated in complete_exit above
+void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
+Thread * const Self = THREAD ;
+assert(Self->is_Java_thread(), "Must be Java thread!");
+JavaThread *jt = (JavaThread *)THREAD;
+DeferredInitialize () ;
+// Throw IMSX or IEX.
+CHECK_OWNER();
+// check for a pending interrupt
+if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
+// post monitor waited event.  Note that this is past-tense, we are done waiting.
+if (JvmtiExport::should_post_monitor_waited()) {
+// Note: 'false' parameter is passed here because the
+// wait was not timed out due to thread interrupt.
+JvmtiExport::post_monitor_waited(jt, this, false);
+}
+TEVENT (Wait - Throw IEX) ;
+THROW(vmSymbols::java_lang_InterruptedException());
+return ;
+}
+TEVENT (Wait) ;
+assert (Self->_Stalled == 0, "invariant") ;
+Self->_Stalled = intptr_t(this) ;
+jt->set_current_waiting_monitor(this);
+// create a node to be put into the queue
+// Critically, after we reset() the event but prior to park(), we must check
+// for a pending interrupt.
+ObjectWaiter node(Self);
+node.TState = ObjectWaiter::TS_WAIT ;
+Self->_ParkEvent->reset() ;
+OrderAccess::fence();          // ST into Event; membar ; LD interrupted-flag
+// Enter the waiting queue, which is a circular doubly linked list in this case
+// but it could be a priority queue or any data structure.
+// _WaitSetLock protects the wait queue.  Normally the wait queue is accessed only
+// by the the owner of the monitor *except* in the case where park()
+// returns because of a timeout of interrupt.  Contention is exceptionally rare
+// so we use a simple spin-lock instead of a heavier-weight blocking lock.
+Thread::SpinAcquire (&_WaitSetLock, "WaitSet - add") ;
+AddWaiter (&node) ;
+Thread::SpinRelease (&_WaitSetLock) ;
+if ((SyncFlags & 4) == 0) {
+_Responsible = NULL ;
+}
+intptr_t save = _recursions; // record the old recursion count
+_waiters++;                  // increment the number of waiters
+_recursions = 0;             // set the recursion level to be 1
+exit (Self) ;                    // exit the monitor
+guarantee (_owner != Self, "invariant") ;
+// As soon as the ObjectMonitor's ownership is dropped in the exit()
+// call above, another thread can enter() the ObjectMonitor, do the
+// notify(), and exit() the ObjectMonitor. If the other thread's
+// exit() call chooses this thread as the successor and the unpark()
+// call happens to occur while this thread is posting a
+// MONITOR_CONTENDED_EXIT event, then we run the risk of the event
+// handler using RawMonitors and consuming the unpark().
+//
+// To avoid the problem, we re-post the event. This does no harm
+// even if the original unpark() was not consumed because we are the
+// chosen successor for this monitor.
+if (node._notified != 0 && _succ == Self) {
+node._event->unpark();
+}
+// The thread is on the WaitSet list - now park() it.
+// On MP systems it's conceivable that a brief spin before we park
+// could be profitable.
+//
+// TODO-FIXME: change the following logic to a loop of the form
+//   while (!timeout && !interrupted && _notified == 0) park()
+int ret = OS_OK ;
+int WasNotified = 0 ;
+{ // State transition wrappers
+OSThread* osthread = Self->osthread();
+OSThreadWaitState osts(osthread, true);
+{
+ThreadBlockInVM tbivm(jt);
+// Thread is in thread_blocked state and oop access is unsafe.
+jt->set_suspend_equivalent();
+if (interruptible && (Thread::is_interrupted(THREAD, false) || HAS_PENDING_EXCEPTION)) {
+// Intentionally empty
+} else
+if (node._notified == 0) {
+if (millis <= 0) {
+Self->_ParkEvent->park () ;
+} else {
+ret = Self->_ParkEvent->park (millis) ;
+}
+}
+// were we externally suspended while we were waiting?
+if (ExitSuspendEquivalent (jt)) {
+// TODO-FIXME: add -- if succ == Self then succ = null.
+jt->java_suspend_self();
+}
+} // Exit thread safepoint: transition _thread_blocked -> _thread_in_vm
+// Node may be on the WaitSet, the EntryList (or cxq), or in transition
+// from the WaitSet to the EntryList.
+// See if we need to remove Node from the WaitSet.
+// We use double-checked locking to avoid grabbing _WaitSetLock
+// if the thread is not on the wait queue.
+//
+// Note that we don't need a fence before the fetch of TState.
+// In the worst case we'll fetch a old-stale value of TS_WAIT previously
+// written by the is thread. (perhaps the fetch might even be satisfied
+// by a look-aside into the processor's own store buffer, although given
+// the length of the code path between the prior ST and this load that's
+// highly unlikely).  If the following LD fetches a stale TS_WAIT value
+// then we'll acquire the lock and then re-fetch a fresh TState value.
+// That is, we fail toward safety.
+if (node.TState == ObjectWaiter::TS_WAIT) {
+Thread::SpinAcquire (&_WaitSetLock, "WaitSet - unlink") ;
+if (node.TState == ObjectWaiter::TS_WAIT) {
+DequeueSpecificWaiter (&node) ;       // unlink from WaitSet
+assert(node._notified == 0, "invariant");
+node.TState = ObjectWaiter::TS_RUN ;
+}
+Thread::SpinRelease (&_WaitSetLock) ;
+}
+// The thread is now either on off-list (TS_RUN),
+// on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
+// The Node's TState variable is stable from the perspective of this thread.
+// No other threads will asynchronously modify TState.
+guarantee (node.TState != ObjectWaiter::TS_WAIT, "invariant") ;
+OrderAccess::loadload() ;
+if (_succ == Self) _succ = NULL ;
+WasNotified = node._notified ;
+// Reentry phase -- reacquire the monitor.
+// re-enter contended monitor after object.wait().
+// retain OBJECT_WAIT state until re-enter successfully completes
+// Thread state is thread_in_vm and oop access is again safe,
+// although the raw address of the object may have changed.
+// (Don't cache naked oops over safepoints, of course).
+// post monitor waited event. Note that this is past-tense, we are done waiting.
+if (JvmtiExport::should_post_monitor_waited()) {
+JvmtiExport::post_monitor_waited(jt, this, ret == OS_TIMEOUT);
+}
+OrderAccess::fence() ;
+assert (Self->_Stalled != 0, "invariant") ;
+Self->_Stalled = 0 ;
+assert (_owner != Self, "invariant") ;
+ObjectWaiter::TStates v = node.TState ;
+if (v == ObjectWaiter::TS_RUN) {
+enter (Self) ;
+} else {
+guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
+ReenterI (Self, &node) ;
+node.wait_reenter_end(this);
+}
+// Self has reacquired the lock.
+// Lifecycle - the node representing Self must not appear on any queues.
+// Node is about to go out-of-scope, but even if it were immortal we wouldn't
+// want residual elements associated with this thread left on any lists.
+guarantee (node.TState == ObjectWaiter::TS_RUN, "invariant") ;
+assert    (_owner == Self, "invariant") ;
+assert    (_succ != Self , "invariant") ;
+} // OSThreadWaitState()
+jt->set_current_waiting_monitor(NULL);
+guarantee (_recursions == 0, "invariant") ;
+_recursions = save;     // restore the old recursion count
+_waiters--;             // decrement the number of waiters
+// Verify a few postconditions
+assert (_owner == Self       , "invariant") ;
+assert (_succ  != Self       , "invariant") ;
+assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
+if (SyncFlags & 32) {
+OrderAccess::fence() ;
+}
+// check if the notification happened
+if (!WasNotified) {
+// no, it could be timeout or Thread.interrupt() or both
+// check for interrupt event, otherwise it is timeout
+if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
+TEVENT (Wait - throw IEX from epilog) ;
+THROW(vmSymbols::java_lang_InterruptedException());
+}
+}
+// NOTE: Spurious wake up will be consider as timeout.
+// Monitor notify has precedence over thread interrupt.
+}
+// Consider:
+// If the lock is cool (cxq == null && succ == null) and we're on an MP system
+// then instead of transferring a thread from the WaitSet to the EntryList
+// we might just dequeue a thread from the WaitSet and directly unpark() it.
+void ObjectMonitor::notify(TRAPS) {
+CHECK_OWNER();
+if (_WaitSet == NULL) {
+TEVENT (Empty-Notify) ;
+return ;
+}
+DTRACE_MONITOR_PROBE(notify, this, object(), THREAD);
+int Policy = Knob_MoveNotifyee ;
+Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notify") ;
+ObjectWaiter * iterator = DequeueWaiter() ;
+if (iterator != NULL) {
+TEVENT (Notify1 - Transfer) ;
+guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
+guarantee (iterator->_notified == 0, "invariant") ;
+if (Policy != 4) {
+iterator->TState = ObjectWaiter::TS_ENTER ;
+}
+iterator->_notified = 1 ;
+ObjectWaiter * List = _EntryList ;
+if (List != NULL) {
+assert (List->_prev == NULL, "invariant") ;
+assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+assert (List != iterator, "invariant") ;
+}
+if (Policy == 0) {       // prepend to EntryList
+if (List == NULL) {
+iterator->_next = iterator->_prev = NULL ;
+_EntryList = iterator ;
+} else {
+List->_prev = iterator ;
+iterator->_next = List ;
+iterator->_prev = NULL ;
+_EntryList = iterator ;
+}
+} else
+if (Policy == 1) {      // append to EntryList
+if (List == NULL) {
+iterator->_next = iterator->_prev = NULL ;
+_EntryList = iterator ;
+} else {
+// CONSIDER:  finding the tail currently requires a linear-time walk of
+// the EntryList.  We can make tail access constant-time by converting to
+// a CDLL instead of using our current DLL.
+ObjectWaiter * Tail ;
+for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
+assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
+Tail->_next = iterator ;
+iterator->_prev = Tail ;
+iterator->_next = NULL ;
+}
+} else
+if (Policy == 2) {      // prepend to cxq
+// prepend to cxq
+if (List == NULL) {
+iterator->_next = iterator->_prev = NULL ;
+_EntryList = iterator ;
+} else {
+iterator->TState = ObjectWaiter::TS_CXQ ;
+for (;;) {
+ObjectWaiter * Front = _cxq ;
+iterator->_next = Front ;
+if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
+break ;
+}
+}
+}
+} else
+if (Policy == 3) {      // append to cxq
+iterator->TState = ObjectWaiter::TS_CXQ ;
+for (;;) {
+ObjectWaiter * Tail ;
+Tail = _cxq ;
+if (Tail == NULL) {
+iterator->_next = NULL ;
+if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
+break ;
+}
+} else {
+while (Tail->_next != NULL) Tail = Tail->_next ;
+Tail->_next = iterator ;
+iterator->_prev = Tail ;
+iterator->_next = NULL ;
+break ;
+}
+}
+} else {
+ParkEvent * ev = iterator->_event ;
+iterator->TState = ObjectWaiter::TS_RUN ;
+OrderAccess::fence() ;
+ev->unpark() ;
+}
+if (Policy < 4) {
+iterator->wait_reenter_begin(this);
+}
+// _WaitSetLock protects the wait queue, not the EntryList.  We could
+// move the add-to-EntryList operation, above, outside the critical section
+// protected by _WaitSetLock.  In practice that's not useful.  With the
+// exception of  wait() timeouts and interrupts the monitor owner
+// is the only thread that grabs _WaitSetLock.  There's almost no contention
+// on _WaitSetLock so it's not profitable to reduce the length of the
+// critical section.
+}
+Thread::SpinRelease (&_WaitSetLock) ;
+if (iterator != NULL && ObjectMonitor::_sync_Notifications != NULL) {
+ObjectMonitor::_sync_Notifications->inc() ;
+}
+}
+void ObjectMonitor::notifyAll(TRAPS) {
+CHECK_OWNER();
+ObjectWaiter* iterator;
+if (_WaitSet == NULL) {
+TEVENT (Empty-NotifyAll) ;
+return ;
+}
+DTRACE_MONITOR_PROBE(notifyAll, this, object(), THREAD);
+int Policy = Knob_MoveNotifyee ;
+int Tally = 0 ;
+Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notifyall") ;
+for (;;) {
+iterator = DequeueWaiter () ;
+if (iterator == NULL) break ;
+TEVENT (NotifyAll - Transfer1) ;
+++Tally ;
+// Disposition - what might we do with iterator ?
+// a.  add it directly to the EntryList - either tail or head.
+// b.  push it onto the front of the _cxq.
+// For now we use (a).
+guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
+guarantee (iterator->_notified == 0, "invariant") ;
+iterator->_notified = 1 ;
+if (Policy != 4) {
+iterator->TState = ObjectWaiter::TS_ENTER ;
+}
+ObjectWaiter * List = _EntryList ;
+if (List != NULL) {
+assert (List->_prev == NULL, "invariant") ;
+assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
+assert (List != iterator, "invariant") ;
+}
+if (Policy == 0) {       // prepend to EntryList
+if (List == NULL) {
+iterator->_next = iterator->_prev = NULL ;
+_EntryList = iterator ;
+} else {
+List->_prev = iterator ;
+iterator->_next = List ;
+iterator->_prev = NULL ;
+_EntryList = iterator ;
+}
+} else
+if (Policy == 1) {      // append to EntryList
+if (List == NULL) {
+iterator->_next = iterator->_prev = NULL ;
+_EntryList = iterator ;
+} else {
+// CONSIDER:  finding the tail currently requires a linear-time walk of
+// the EntryList.  We can make tail access constant-time by converting to
+// a CDLL instead of using our current DLL.
+ObjectWaiter * Tail ;
+for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
+assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
+Tail->_next = iterator ;
+iterator->_prev = Tail ;
+iterator->_next = NULL ;
+}
+} else
+if (Policy == 2) {      // prepend to cxq
+// prepend to cxq
+iterator->TState = ObjectWaiter::TS_CXQ ;
+for (;;) {
+ObjectWaiter * Front = _cxq ;
+iterator->_next = Front ;
+if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
+break ;
+}
+}
+} else
+if (Policy == 3) {      // append to cxq
+iterator->TState = ObjectWaiter::TS_CXQ ;
+for (;;) {
+ObjectWaiter * Tail ;
+Tail = _cxq ;
+if (Tail == NULL) {
+iterator->_next = NULL ;
+if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
+break ;
+}
+} else {
+while (Tail->_next != NULL) Tail = Tail->_next ;
+Tail->_next = iterator ;
+iterator->_prev = Tail ;
+iterator->_next = NULL ;
+break ;
+}
+}
+} else {
+ParkEvent * ev = iterator->_event ;
+iterator->TState = ObjectWaiter::TS_RUN ;
+OrderAccess::fence() ;
+ev->unpark() ;
+}
+if (Policy < 4) {
+iterator->wait_reenter_begin(this);
+}
+// _WaitSetLock protects the wait queue, not the EntryList.  We could
+// move the add-to-EntryList operation, above, outside the critical section
+// protected by _WaitSetLock.  In practice that's not useful.  With the
+// exception of  wait() timeouts and interrupts the monitor owner
+// is the only thread that grabs _WaitSetLock.  There's almost no contention
+// on _WaitSetLock so it's not profitable to reduce the length of the
+// critical section.
+}
+Thread::SpinRelease (&_WaitSetLock) ;
+if (Tally != 0 && ObjectMonitor::_sync_Notifications != NULL) {
+ObjectMonitor::_sync_Notifications->inc(Tally) ;
+}
+}
+// -----------------------------------------------------------------------------
+// Adaptive Spinning Support
+//
+// Adaptive spin-then-block - rational spinning
+//
+// Note that we spin "globally" on _owner with a classic SMP-polite TATAS
+// algorithm.  On high order SMP systems it would be better to start with
+// a brief global spin and then revert to spinning locally.  In the spirit of MCS/CLH,
+// a contending thread could enqueue itself on the cxq and then spin locally
+// on a thread-specific variable such as its ParkEvent._Event flag.
+// That's left as an exercise for the reader.  Note that global spinning is
+// not problematic on Niagara, as the L2$ serves the interconnect and has both
+// low latency and massive bandwidth.
+//
+// Broadly, we can fix the spin frequency -- that is, the % of contended lock
+// acquisition attempts where we opt to spin --  at 100% and vary the spin count
+// (duration) or we can fix the count at approximately the duration of
+// a context switch and vary the frequency.   Of course we could also
+// vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
+// See http://j2se.east/~dice/PERSIST/040824-AdaptiveSpinning.html.
+//
+// This implementation varies the duration "D", where D varies with
+// the success rate of recent spin attempts. (D is capped at approximately
+// length of a round-trip context switch).  The success rate for recent
+// spin attempts is a good predictor of the success rate of future spin
+// attempts.  The mechanism adapts automatically to varying critical
+// section length (lock modality), system load and degree of parallelism.
+// D is maintained per-monitor in _SpinDuration and is initialized
+// optimistically.  Spin frequency is fixed at 100%.
+//
+// Note that _SpinDuration is volatile, but we update it without locks
+// or atomics.  The code is designed so that _SpinDuration stays within
+// a reasonable range even in the presence of races.  The arithmetic
+// operations on _SpinDuration are closed over the domain of legal values,
+// so at worst a race will install and older but still legal value.
+// At the very worst this introduces some apparent non-determinism.
+// We might spin when we shouldn't or vice-versa, but since the spin
+// count are relatively short, even in the worst case, the effect is harmless.
+//
+// Care must be taken that a low "D" value does not become an
+// an absorbing state.  Transient spinning failures -- when spinning
+// is overall profitable -- should not cause the system to converge
+// on low "D" values.  We want spinning to be stable and predictable
+// and fairly responsive to change and at the same time we don't want
+// it to oscillate, become metastable, be "too" non-deterministic,
+// or converge on or enter undesirable stable absorbing states.
+//
+// We implement a feedback-based control system -- using past behavior
+// to predict future behavior.  We face two issues: (a) if the
+// input signal is random then the spin predictor won't provide optimal
+// results, and (b) if the signal frequency is too high then the control
+// system, which has some natural response lag, will "chase" the signal.
+// (b) can arise from multimodal lock hold times.  Transient preemption
+// can also result in apparent bimodal lock hold times.
+// Although sub-optimal, neither condition is particularly harmful, as
+// in the worst-case we'll spin when we shouldn't or vice-versa.
+// The maximum spin duration is rather short so the failure modes aren't bad.
+// To be conservative, I've tuned the gain in system to bias toward
+// _not spinning.  Relatedly, the system can sometimes enter a mode where it
+// "rings" or oscillates between spinning and not spinning.  This happens
+// when spinning is just on the cusp of profitability, however, so the
+// situation is not dire.  The state is benign -- there's no need to add
+// hysteresis control to damp the transition rate between spinning and
+// not spinning.
+//
+intptr_t ObjectMonitor::SpinCallbackArgument = 0 ;
+int (*ObjectMonitor::SpinCallbackFunction)(intptr_t, int) = NULL ;
+// Spinning: Fixed frequency (100%), vary duration
+int ObjectMonitor::TrySpin_VaryDuration (Thread * Self) {
+// Dumb, brutal spin.  Good for comparative measurements against adaptive spinning.
+int ctr = Knob_FixedSpin ;
+if (ctr != 0) {
+while (--ctr >= 0) {
+if (TryLock (Self) > 0) return 1 ;
+SpinPause () ;
+}
+return 0 ;
+}
+for (ctr = Knob_PreSpin + 1; --ctr >= 0 ; ) {
+if (TryLock(Self) > 0) {
+// Increase _SpinDuration ...
+// Note that we don't clamp SpinDuration precisely at SpinLimit.
+// Raising _SpurDuration to the poverty line is key.
+int x = _SpinDuration ;
+if (x < Knob_SpinLimit) {
+if (x < Knob_Poverty) x = Knob_Poverty ;
+_SpinDuration = x + Knob_BonusB ;
+}
+return 1 ;
+}
+SpinPause () ;
+}
+// Admission control - verify preconditions for spinning
+//
+// We always spin a little bit, just to prevent _SpinDuration == 0 from
+// becoming an absorbing state.  Put another way, we spin briefly to
+// sample, just in case the system load, parallelism, contention, or lock
+// modality changed.
+//
+// Consider the following alternative:
+// Periodically set _SpinDuration = _SpinLimit and try a long/full
+// spin attempt.  "Periodically" might mean after a tally of
+// the # of failed spin attempts (or iterations) reaches some threshold.
+// This takes us into the realm of 1-out-of-N spinning, where we
+// hold the duration constant but vary the frequency.
+ctr = _SpinDuration  ;
+if (ctr < Knob_SpinBase) ctr = Knob_SpinBase ;
+if (ctr <= 0) return 0 ;
+if (Knob_SuccRestrict && _succ != NULL) return 0 ;
+if (Knob_OState && NotRunnable (Self, (Thread *) _owner)) {
+TEVENT (Spin abort - notrunnable [TOP]);
+return 0 ;
+}
+int MaxSpin = Knob_MaxSpinners ;
+if (MaxSpin >= 0) {
+if (_Spinner > MaxSpin) {
+TEVENT (Spin abort -- too many spinners) ;
+return 0 ;
+}
+// Slighty racy, but benign ...
+Adjust (&_Spinner, 1) ;
+}
+// We're good to spin ... spin ingress.
+// CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
+// when preparing to LD...CAS _owner, etc and the CAS is likely
+// to succeed.
+int hits    = 0 ;
+int msk     = 0 ;
+int caspty  = Knob_CASPenalty ;
+int oxpty   = Knob_OXPenalty ;
+int sss     = Knob_SpinSetSucc ;
+if (sss && _succ == NULL ) _succ = Self ;
+Thread * prv = NULL ;
+// There are three ways to exit the following loop:
+// 1.  A successful spin where this thread has acquired the lock.
+// 2.  Spin failure with prejudice
+// 3.  Spin failure without prejudice
+while (--ctr >= 0) {
+// Periodic polling -- Check for pending GC
+// Threads may spin while they're unsafe.
+// We don't want spinning threads to delay the JVM from reaching
+// a stop-the-world safepoint or to steal cycles from GC.
+// If we detect a pending safepoint we abort in order that
+// (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
+// this thread, if safe, doesn't steal cycles from GC.
+// This is in keeping with the "no loitering in runtime" rule.
+// We periodically check to see if there's a safepoint pending.
+if ((ctr & 0xFF) == 0) {
+if (SafepointSynchronize::do_call_back()) {
+TEVENT (Spin: safepoint) ;
+goto Abort ;           // abrupt spin egress
+}
+if (Knob_UsePause & 1) SpinPause () ;
+int (*scb)(intptr_t,int) = SpinCallbackFunction ;
+if (hits > 50 && scb != NULL) {
+int abend = (*scb)(SpinCallbackArgument, 0) ;
+}
+}
+if (Knob_UsePause & 2) SpinPause() ;
+// Exponential back-off ...  Stay off the bus to reduce coherency traffic.
+// This is useful on classic SMP systems, but is of less utility on
+// N1-style CMT platforms.
+//
+// Trade-off: lock acquisition latency vs coherency bandwidth.
+// Lock hold times are typically short.  A histogram
+// of successful spin attempts shows that we usually acquire
+// the lock early in the spin.  That suggests we want to
+// sample _owner frequently in the early phase of the spin,
+// but then back-off and sample less frequently as the spin
+// progresses.  The back-off makes a good citizen on SMP big
+// SMP systems.  Oversampling _owner can consume excessive
+// coherency bandwidth.  Relatedly, if we _oversample _owner we
+// can inadvertently interfere with the the ST m->owner=null.
+// executed by the lock owner.
+if (ctr & msk) continue ;
+++hits ;
+if ((hits & 0xF) == 0) {
+// The 0xF, above, corresponds to the exponent.
+// Consider: (msk+1)|msk
+msk = ((msk << 2)|3) & BackOffMask ;
+}
+// Probe _owner with TATAS
+// If this thread observes the monitor transition or flicker
+// from locked to unlocked to locked, then the odds that this
+// thread will acquire the lock in this spin attempt go down
+// considerably.  The same argument applies if the CAS fails
+// or if we observe _owner change from one non-null value to
+// another non-null value.   In such cases we might abort
+// the spin without prejudice or apply a "penalty" to the
+// spin count-down variable "ctr", reducing it by 100, say.
+Thread * ox = (Thread *) _owner ;
+if (ox == NULL) {
+ox = (Thread *) Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
+if (ox == NULL) {
+// The CAS succeeded -- this thread acquired ownership
+// Take care of some bookkeeping to exit spin state.
+if (sss && _succ == Self) {
+_succ = NULL ;
+}
+if (MaxSpin > 0) Adjust (&_Spinner, -1) ;
+// Increase _SpinDuration :
+// The spin was successful (profitable) so we tend toward
+// longer spin attempts in the future.
+// CONSIDER: factor "ctr" into the _SpinDuration adjustment.
+// If we acquired the lock early in the spin cycle it
+// makes sense to increase _SpinDuration proportionally.
+// Note that we don't clamp SpinDuration precisely at SpinLimit.
+int x = _SpinDuration ;
+if (x < Knob_SpinLimit) {
+if (x < Knob_Poverty) x = Knob_Poverty ;
+_SpinDuration = x + Knob_Bonus ;
+}
+return 1 ;
+}
+// The CAS failed ... we can take any of the following actions:
+// * penalize: ctr -= Knob_CASPenalty
+// * exit spin with prejudice -- goto Abort;
+// * exit spin without prejudice.
+// * Since CAS is high-latency, retry again immediately.
+prv = ox ;
+TEVENT (Spin: cas failed) ;
+if (caspty == -2) break ;
+if (caspty == -1) goto Abort ;
+ctr -= caspty ;
+continue ;
+}
+// Did lock ownership change hands ?
+if (ox != prv && prv != NULL ) {
+TEVENT (spin: Owner changed)
+if (oxpty == -2) break ;
+if (oxpty == -1) goto Abort ;
+ctr -= oxpty ;
+}
+prv = ox ;
+// Abort the spin if the owner is not executing.
+// The owner must be executing in order to drop the lock.
+// Spinning while the owner is OFFPROC is idiocy.
+// Consider: ctr -= RunnablePenalty ;
+if (Knob_OState && NotRunnable (Self, ox)) {
+TEVENT (Spin abort - notrunnable);
+goto Abort ;
+}
+if (sss && _succ == NULL ) _succ = Self ;
+}
+// Spin failed with prejudice -- reduce _SpinDuration.
+// TODO: Use an AIMD-like policy to adjust _SpinDuration.
+// AIMD is globally stable.
+TEVENT (Spin failure) ;
+{
+int x = _SpinDuration ;
+if (x > 0) {
+// Consider an AIMD scheme like: x -= (x >> 3) + 100
+// This is globally sample and tends to damp the response.
+x -= Knob_Penalty ;
+if (x < 0) x = 0 ;
+_SpinDuration = x ;
+}
+}
+Abort:
+if (MaxSpin >= 0) Adjust (&_Spinner, -1) ;
+if (sss && _succ == Self) {
+_succ = NULL ;
+// Invariant: after setting succ=null a contending thread
+// must recheck-retry _owner before parking.  This usually happens
+// in the normal usage of TrySpin(), but it's safest
+// to make TrySpin() as foolproof as possible.
+OrderAccess::fence() ;
+if (TryLock(Self) > 0) return 1 ;
+}
+return 0 ;
+}
+// NotRunnable() -- informed spinning
+//
+// Don't bother spinning if the owner is not eligible to drop the lock.
+// Peek at the owner's schedctl.sc_state and Thread._thread_values and
+// spin only if the owner thread is _thread_in_Java or _thread_in_vm.
+// The thread must be runnable in order to drop the lock in timely fashion.
+// If the _owner is not runnable then spinning will not likely be
+// successful (profitable).
+//
+// Beware -- the thread referenced by _owner could have died
+// so a simply fetch from _owner->_thread_state might trap.
+// Instead, we use SafeFetchXX() to safely LD _owner->_thread_state.
+// Because of the lifecycle issues the schedctl and _thread_state values
+// observed by NotRunnable() might be garbage.  NotRunnable must
+// tolerate this and consider the observed _thread_state value
+// as advisory.
+//
+// Beware too, that _owner is sometimes a BasicLock address and sometimes
+// a thread pointer.  We differentiate the two cases with OwnerIsThread.
+// Alternately, we might tag the type (thread pointer vs basiclock pointer)
+// with the LSB of _owner.  Another option would be to probablistically probe
+// the putative _owner->TypeTag value.
+//
+// Checking _thread_state isn't perfect.  Even if the thread is
+// in_java it might be blocked on a page-fault or have been preempted
+// and sitting on a ready/dispatch queue.  _thread state in conjunction
+// with schedctl.sc_state gives us a good picture of what the
+// thread is doing, however.
+//
+// TODO: check schedctl.sc_state.
+// We'll need to use SafeFetch32() to read from the schedctl block.
+// See RFE #5004247 and http://sac.sfbay.sun.com/Archives/CaseLog/arc/PSARC/2005/351/
+//
+// The return value from NotRunnable() is *advisory* -- the
+// result is based on sampling and is not necessarily coherent.
+// The caller must tolerate false-negative and false-positive errors.
+// Spinning, in general, is probabilistic anyway.
+int ObjectMonitor::NotRunnable (Thread * Self, Thread * ox) {
+// Check either OwnerIsThread or ox->TypeTag == 2BAD.
+if (!OwnerIsThread) return 0 ;
+if (ox == NULL) return 0 ;
+// Avoid transitive spinning ...
+// Say T1 spins or blocks trying to acquire L.  T1._Stalled is set to L.
+// Immediately after T1 acquires L it's possible that T2, also
+// spinning on L, will see L.Owner=T1 and T1._Stalled=L.
+// This occurs transiently after T1 acquired L but before
+// T1 managed to clear T1.Stalled.  T2 does not need to abort
+// its spin in this circumstance.
+intptr_t BlockedOn = SafeFetchN ((intptr_t *) &ox->_Stalled, intptr_t(1)) ;
+if (BlockedOn == 1) return 1 ;
+if (BlockedOn != 0) {
+return BlockedOn != intptr_t(this) && _owner == ox ;
+}
+assert (sizeof(((JavaThread *)ox)->_thread_state == sizeof(int)), "invariant") ;
+int jst = SafeFetch32 ((int *) &((JavaThread *) ox)->_thread_state, -1) ; ;
+// consider also: jst != _thread_in_Java -- but that's overspecific.
+return jst == _thread_blocked || jst == _thread_in_native ;
+}
+// -----------------------------------------------------------------------------
+// WaitSet management ...
+ObjectWaiter::ObjectWaiter(Thread* thread) {
+_next     = NULL;
+_prev     = NULL;
+_notified = 0;
+TState    = TS_RUN ;
+_thread   = thread;
+_event    = thread->_ParkEvent ;
+_active   = false;
+assert (_event != NULL, "invariant") ;
+}
+void ObjectWaiter::wait_reenter_begin(ObjectMonitor *mon) {
+JavaThread *jt = (JavaThread *)this->_thread;
+_active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(jt, mon);
+}
+void ObjectWaiter::wait_reenter_end(ObjectMonitor *mon) {
+JavaThread *jt = (JavaThread *)this->_thread;
+JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(jt, _active);
+}
+inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
+assert(node != NULL, "should not dequeue NULL node");
+assert(node->_prev == NULL, "node already in list");
+assert(node->_next == NULL, "node already in list");
+// put node at end of queue (circular doubly linked list)
+if (_WaitSet == NULL) {
+_WaitSet = node;
+node->_prev = node;
+node->_next = node;
+} else {
+ObjectWaiter* head = _WaitSet ;
+ObjectWaiter* tail = head->_prev;
+assert(tail->_next == head, "invariant check");
+tail->_next = node;
+head->_prev = node;
+node->_next = head;
+node->_prev = tail;
+}
+}
+inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
+// dequeue the very first waiter
+ObjectWaiter* waiter = _WaitSet;
+if (waiter) {
+DequeueSpecificWaiter(waiter);
+}
+return waiter;
+}
+inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
+assert(node != NULL, "should not dequeue NULL node");
+assert(node->_prev != NULL, "node already removed from list");
+assert(node->_next != NULL, "node already removed from list");
+// when the waiter has woken up because of interrupt,
+// timeout or other spurious wake-up, dequeue the
+// waiter from waiting list
+ObjectWaiter* next = node->_next;
+if (next == node) {
+assert(node->_prev == node, "invariant check");
+_WaitSet = NULL;
+} else {
+ObjectWaiter* prev = node->_prev;
+assert(prev->_next == node, "invariant check");
+assert(next->_prev == node, "invariant check");
+next->_prev = prev;
+prev->_next = next;
+if (_WaitSet == node) {
+_WaitSet = next;
+}
+}
+node->_next = NULL;
+node->_prev = NULL;
+}
+// -----------------------------------------------------------------------------
+// PerfData support
+PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts       = NULL ;
+PerfCounter * ObjectMonitor::_sync_FutileWakeups               = NULL ;
+PerfCounter * ObjectMonitor::_sync_Parks                       = NULL ;
+PerfCounter * ObjectMonitor::_sync_EmptyNotifications          = NULL ;
+PerfCounter * ObjectMonitor::_sync_Notifications               = NULL ;
+PerfCounter * ObjectMonitor::_sync_PrivateA                    = NULL ;
+PerfCounter * ObjectMonitor::_sync_PrivateB                    = NULL ;
+PerfCounter * ObjectMonitor::_sync_SlowExit                    = NULL ;
+PerfCounter * ObjectMonitor::_sync_SlowEnter                   = NULL ;
+PerfCounter * ObjectMonitor::_sync_SlowNotify                  = NULL ;
+PerfCounter * ObjectMonitor::_sync_SlowNotifyAll               = NULL ;
+PerfCounter * ObjectMonitor::_sync_FailedSpins                 = NULL ;
+PerfCounter * ObjectMonitor::_sync_SuccessfulSpins             = NULL ;
+PerfCounter * ObjectMonitor::_sync_MonInCirculation            = NULL ;
+PerfCounter * ObjectMonitor::_sync_MonScavenged                = NULL ;
+PerfCounter * ObjectMonitor::_sync_Inflations                  = NULL ;
+PerfCounter * ObjectMonitor::_sync_Deflations                  = NULL ;
+PerfLongVariable * ObjectMonitor::_sync_MonExtant              = NULL ;
+// One-shot global initialization for the sync subsystem.
+// We could also defer initialization and initialize on-demand
+// the first time we call inflate().  Initialization would
+// be protected - like so many things - by the MonitorCache_lock.
+void ObjectMonitor::Initialize () {
+static int InitializationCompleted = 0 ;
+assert (InitializationCompleted == 0, "invariant") ;
+InitializationCompleted = 1 ;
+if (UsePerfData) {
+EXCEPTION_MARK ;
+#define NEWPERFCOUNTER(n)   {n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,CHECK); }
+#define NEWPERFVARIABLE(n)  {n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,CHECK); }
+NEWPERFCOUNTER(_sync_Inflations) ;
+NEWPERFCOUNTER(_sync_Deflations) ;
+NEWPERFCOUNTER(_sync_ContendedLockAttempts) ;
+NEWPERFCOUNTER(_sync_FutileWakeups) ;
+NEWPERFCOUNTER(_sync_Parks) ;
+NEWPERFCOUNTER(_sync_EmptyNotifications) ;
+NEWPERFCOUNTER(_sync_Notifications) ;
+NEWPERFCOUNTER(_sync_SlowEnter) ;
+NEWPERFCOUNTER(_sync_SlowExit) ;
+NEWPERFCOUNTER(_sync_SlowNotify) ;
+NEWPERFCOUNTER(_sync_SlowNotifyAll) ;
+NEWPERFCOUNTER(_sync_FailedSpins) ;
+NEWPERFCOUNTER(_sync_SuccessfulSpins) ;
+NEWPERFCOUNTER(_sync_PrivateA) ;
+NEWPERFCOUNTER(_sync_PrivateB) ;
+NEWPERFCOUNTER(_sync_MonInCirculation) ;
+NEWPERFCOUNTER(_sync_MonScavenged) ;
+NEWPERFVARIABLE(_sync_MonExtant) ;
+#undef NEWPERFCOUNTER
+}
+}
+// Compile-time asserts
+// When possible, it's better to catch errors deterministically at
+// compile-time than at runtime.  The down-side to using compile-time
+// asserts is that error message -- often something about negative array
+// indices -- is opaque.
+#define CTASSERT(x) { int tag[1-(2*!(x))]; printf ("Tag @" INTPTR_FORMAT "\n", (intptr_t)tag); }
+void ObjectMonitor::ctAsserts() {
+CTASSERT(offset_of (ObjectMonitor, _header) == 0);
+}
+static char * kvGet (char * kvList, const char * Key) {
+if (kvList == NULL) return NULL ;
+size_t n = strlen (Key) ;
+char * Search ;
+for (Search = kvList ; *Search ; Search += strlen(Search) + 1) {
+if (strncmp (Search, Key, n) == 0) {
+if (Search[n] == '=') return Search + n + 1 ;
+if (Search[n] == 0)   return (char *) "1" ;
+}
+}
+return NULL ;
+}
+static int kvGetInt (char * kvList, const char * Key, int Default) {
+char * v = kvGet (kvList, Key) ;
+int rslt = v ? ::strtol (v, NULL, 0) : Default ;
+if (Knob_ReportSettings && v != NULL) {
+::printf ("  SyncKnob: %s %d(%d)\n", Key, rslt, Default) ;
+::fflush (stdout) ;
+}
+return rslt ;
+}
+void ObjectMonitor::DeferredInitialize () {
+if (InitDone > 0) return ;
+if (Atomic::cmpxchg (-1, &InitDone, 0) != 0) {
+while (InitDone != 1) ;
+return ;
+}
+// One-shot global initialization ...
+// The initialization is idempotent, so we don't need locks.
+// In the future consider doing this via os::init_2().
+// SyncKnobs consist of <Key>=<Value> pairs in the style
+// of environment variables.  Start by converting ':' to NUL.
+if (SyncKnobs == NULL) SyncKnobs = "" ;
+size_t sz = strlen (SyncKnobs) ;
+char * knobs = (char *) malloc (sz + 2) ;
+if (knobs == NULL) {
+vm_exit_out_of_memory (sz + 2, "Parse SyncKnobs") ;
+guarantee (0, "invariant") ;
+}
+strcpy (knobs, SyncKnobs) ;
+knobs[sz+1] = 0 ;
+for (char * p = knobs ; *p ; p++) {
+if (*p == ':') *p = 0 ;
+}
+#define SETKNOB(x) { Knob_##x = kvGetInt (knobs, #x, Knob_##x); }
+SETKNOB(ReportSettings) ;
+SETKNOB(Verbose) ;
+SETKNOB(FixedSpin) ;
+SETKNOB(SpinLimit) ;
+SETKNOB(SpinBase) ;
+SETKNOB(SpinBackOff);
+SETKNOB(CASPenalty) ;
+SETKNOB(OXPenalty) ;
+SETKNOB(LogSpins) ;
+SETKNOB(SpinSetSucc) ;
+SETKNOB(SuccEnabled) ;
+SETKNOB(SuccRestrict) ;
+SETKNOB(Penalty) ;
+SETKNOB(Bonus) ;
+SETKNOB(BonusB) ;
+SETKNOB(Poverty) ;
+SETKNOB(SpinAfterFutile) ;
+SETKNOB(UsePause) ;
+SETKNOB(SpinEarly) ;
+SETKNOB(OState) ;
+SETKNOB(MaxSpinners) ;
+SETKNOB(PreSpin) ;
+SETKNOB(ExitPolicy) ;
+SETKNOB(QMode);
+SETKNOB(ResetEvent) ;
+SETKNOB(MoveNotifyee) ;
+SETKNOB(FastHSSEC) ;
+#undef SETKNOB
+if (os::is_MP()) {
+BackOffMask = (1 << Knob_SpinBackOff) - 1 ;
+if (Knob_ReportSettings) ::printf ("BackOffMask=%X\n", BackOffMask) ;
+// CONSIDER: BackOffMask = ROUNDUP_NEXT_POWER2 (ncpus-1)
+} else {
+Knob_SpinLimit = 0 ;
+Knob_SpinBase  = 0 ;
+Knob_PreSpin   = 0 ;
+Knob_FixedSpin = -1 ;
+}
+if (Knob_LogSpins == 0) {
+ObjectMonitor::_sync_FailedSpins = NULL ;
+}
+free (knobs) ;
+OrderAccess::fence() ;
+InitDone = 1 ;
+}
+#ifndef PRODUCT
+void ObjectMonitor::verify() {
+}
+void ObjectMonitor::print() {
+}
+#endif

changeset 6975	dc9b63952682
child 7397	5b173b4ca846