author | kvn |
Mon, 09 Aug 2010 15:17:05 -0700 (2010-08-09) | |
changeset 6183 | 4c74cfe14f20 |
parent 5547 | f4b087cbb361 |
child 7397 | 5b173b4ca846 |
permissions | -rw-r--r-- |
1 | 1 |
/* |
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* Copyright (c) 1997, 2009, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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||
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// The direct lock/unlock calls do not force a collection if an unlock |
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// decrements the count to zero. Avoid calling these if at all possible. |
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class GC_locker: public AllStatic { |
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private: |
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static volatile jint _jni_lock_count; // number of jni active instances |
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static volatile jint _lock_count; // number of other active instances |
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static volatile bool _needs_gc; // heap is filling, we need a GC |
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// note: bool is typedef'd as jint |
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static volatile bool _doing_gc; // unlock_critical() is doing a GC |
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// Accessors |
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static bool is_jni_active() { |
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return _jni_lock_count > 0; |
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} |
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static void set_needs_gc() { |
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assert(SafepointSynchronize::is_at_safepoint(), |
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"needs_gc is only set at a safepoint"); |
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_needs_gc = true; |
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} |
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static void clear_needs_gc() { |
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assert_lock_strong(JNICritical_lock); |
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_needs_gc = false; |
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} |
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static void jni_lock() { |
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Atomic::inc(&_jni_lock_count); |
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CHECK_UNHANDLED_OOPS_ONLY( |
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if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; }) |
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assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(), |
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"locking failed"); |
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} |
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static void jni_unlock() { |
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Atomic::dec(&_jni_lock_count); |
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CHECK_UNHANDLED_OOPS_ONLY( |
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if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; }) |
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} |
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static void jni_lock_slow(); |
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static void jni_unlock_slow(); |
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public: |
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// Accessors |
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static bool is_active(); |
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static bool needs_gc() { return _needs_gc; } |
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// Shorthand |
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static bool is_active_and_needs_gc() { return is_active() && needs_gc();} |
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// Calls set_needs_gc() if is_active() is true. Returns is_active(). |
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static bool check_active_before_gc(); |
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// Stalls the caller (who should not be in a jni critical section) |
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// until needs_gc() clears. Note however that needs_gc() may be |
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// set at a subsequent safepoint and/or cleared under the |
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// JNICritical_lock, so the caller may not safely assert upon |
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// return from this method that "!needs_gc()" since that is |
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// not a stable predicate. |
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static void stall_until_clear(); |
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// Non-structured GC locking: currently needed for JNI. Use with care! |
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static void lock(); |
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static void unlock(); |
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// The following two methods are used for JNI critical regions. |
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// If we find that we failed to perform a GC because the GC_locker |
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// was active, arrange for one as soon as possible by allowing |
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// all threads in critical regions to complete, but not allowing |
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// other critical regions to be entered. The reasons for that are: |
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// 1) a GC request won't be starved by overlapping JNI critical |
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// region activities, which can cause unnecessary OutOfMemory errors. |
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// 2) even if allocation requests can still be satisfied before GC locker |
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// becomes inactive, for example, in tenured generation possibly with |
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// heap expansion, those allocations can trigger lots of safepointing |
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// attempts (ineffective GC attempts) and require Heap_lock which |
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// slow down allocations tremendously. |
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// |
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// Note that critical regions can be nested in a single thread, so |
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// we must allow threads already in critical regions to continue. |
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// |
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// JNI critical regions are the only participants in this scheme |
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// because they are, by spec, well bounded while in a critical region. |
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// |
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// Each of the following two method is split into a fast path and a slow |
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// path. JNICritical_lock is only grabbed in the slow path. |
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// _needs_gc is initially false and every java thread will go |
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// through the fast path (which does the same thing as the slow path |
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// when _needs_gc is false). When GC happens at a safepoint, |
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// GC_locker::is_active() is checked. Since there is no safepoint in the |
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// fast path of lock_critical() and unlock_critical(), there is no race |
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// condition between the fast path and GC. After _needs_gc is set at a |
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// safepoint, every thread will go through the slow path after the safepoint. |
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// Since after a safepoint, each of the following two methods is either |
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// entered from the method entry and falls into the slow path, or is |
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// resumed from the safepoints in the method, which only exist in the slow |
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// path. So when _needs_gc is set, the slow path is always taken, till |
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// _needs_gc is cleared. |
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static void lock_critical(JavaThread* thread); |
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static void unlock_critical(JavaThread* thread); |
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}; |
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// A No_GC_Verifier object can be placed in methods where one assumes that |
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// no garbage collection will occur. The destructor will verify this property |
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// unless the constructor is called with argument false (not verifygc). |
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// |
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// The check will only be done in debug mode and if verifygc true. |
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class No_GC_Verifier: public StackObj { |
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friend class Pause_No_GC_Verifier; |
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protected: |
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bool _verifygc; |
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unsigned int _old_invocations; |
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public: |
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#ifdef ASSERT |
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No_GC_Verifier(bool verifygc = true); |
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~No_GC_Verifier(); |
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#else |
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No_GC_Verifier(bool verifygc = true) {} |
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~No_GC_Verifier() {} |
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#endif |
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}; |
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// A Pause_No_GC_Verifier is used to temporarily pause the behavior |
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// of a No_GC_Verifier object. If we are not in debug mode or if the |
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// No_GC_Verifier object has a _verifygc value of false, then there |
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// is nothing to do. |
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class Pause_No_GC_Verifier: public StackObj { |
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private: |
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No_GC_Verifier * _ngcv; |
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public: |
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#ifdef ASSERT |
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Pause_No_GC_Verifier(No_GC_Verifier * ngcv); |
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~Pause_No_GC_Verifier(); |
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#else |
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Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {} |
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~Pause_No_GC_Verifier() {} |
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#endif |
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}; |
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// A No_Safepoint_Verifier object will throw an assertion failure if |
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// the current thread passes a possible safepoint while this object is |
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// instantiated. A safepoint, will either be: an oop allocation, blocking |
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// on a Mutex or JavaLock, or executing a VM operation. |
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// |
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// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier |
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// |
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class No_Safepoint_Verifier : public No_GC_Verifier { |
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friend class Pause_No_Safepoint_Verifier; |
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private: |
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bool _activated; |
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Thread *_thread; |
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public: |
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#ifdef ASSERT |
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No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) : |
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No_GC_Verifier(verifygc), |
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_activated(activated) { |
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_thread = Thread::current(); |
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if (_activated) { |
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_thread->_allow_allocation_count++; |
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_thread->_allow_safepoint_count++; |
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} |
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} |
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~No_Safepoint_Verifier() { |
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if (_activated) { |
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_thread->_allow_allocation_count--; |
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_thread->_allow_safepoint_count--; |
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} |
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} |
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#else |
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No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){} |
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~No_Safepoint_Verifier() {} |
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#endif |
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}; |
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// A Pause_No_Safepoint_Verifier is used to temporarily pause the |
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// behavior of a No_Safepoint_Verifier object. If we are not in debug |
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// mode then there is nothing to do. If the No_Safepoint_Verifier |
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// object has an _activated value of false, then there is nothing to |
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// do for safepoint and allocation checking, but there may still be |
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// something to do for the underlying No_GC_Verifier object. |
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class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier { |
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private: |
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No_Safepoint_Verifier * _nsv; |
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public: |
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#ifdef ASSERT |
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Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv) |
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: Pause_No_GC_Verifier(nsv) { |
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_nsv = nsv; |
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if (_nsv->_activated) { |
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_nsv->_thread->_allow_allocation_count--; |
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_nsv->_thread->_allow_safepoint_count--; |
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} |
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} |
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~Pause_No_Safepoint_Verifier() { |
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if (_nsv->_activated) { |
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_nsv->_thread->_allow_allocation_count++; |
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_nsv->_thread->_allow_safepoint_count++; |
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} |
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} |
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#else |
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Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv) |
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: Pause_No_GC_Verifier(nsv) {} |
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~Pause_No_Safepoint_Verifier() {} |
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#endif |
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}; |
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// A SkipGCALot object is used to elide the usual effect of gc-a-lot |
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// over a section of execution by a thread. Currently, it's used only to |
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// prevent re-entrant calls to GC. |
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class SkipGCALot : public StackObj { |
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private: |
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bool _saved; |
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Thread* _t; |
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public: |
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#ifdef ASSERT |
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SkipGCALot(Thread* t) : _t(t) { |
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_saved = _t->skip_gcalot(); |
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_t->set_skip_gcalot(true); |
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} |
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~SkipGCALot() { |
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assert(_t->skip_gcalot(), "Save-restore protocol invariant"); |
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_t->set_skip_gcalot(_saved); |
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} |
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#else |
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SkipGCALot(Thread* t) { } |
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~SkipGCALot() { } |
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#endif |
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}; |
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// JRT_LEAF currently can be called from either _thread_in_Java or |
271 |
// _thread_in_native mode. In _thread_in_native, it is ok |
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272 |
// for another thread to trigger GC. The rest of the JRT_LEAF |
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// rules apply. |
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274 |
class JRT_Leaf_Verifier : public No_Safepoint_Verifier { |
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275 |
static bool should_verify_GC(); |
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public: |
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#ifdef ASSERT |
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278 |
JRT_Leaf_Verifier(); |
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279 |
~JRT_Leaf_Verifier(); |
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280 |
#else |
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281 |
JRT_Leaf_Verifier() {} |
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282 |
~JRT_Leaf_Verifier() {} |
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283 |
#endif |
|
284 |
}; |
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286 |
// A No_Alloc_Verifier object can be placed in methods where one assumes that |
|
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// no allocation will occur. The destructor will verify this property |
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// unless the constructor is called with argument false (not activated). |
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// |
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290 |
// The check will only be done in debug mode and if activated. |
|
291 |
// Note: this only makes sense at safepoints (otherwise, other threads may |
|
292 |
// allocate concurrently.) |
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293 |
||
294 |
class No_Alloc_Verifier : public StackObj { |
|
295 |
private: |
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296 |
bool _activated; |
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297 |
||
298 |
public: |
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299 |
#ifdef ASSERT |
|
300 |
No_Alloc_Verifier(bool activated = true) { |
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301 |
_activated = activated; |
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302 |
if (_activated) Thread::current()->_allow_allocation_count++; |
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303 |
} |
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304 |
||
305 |
~No_Alloc_Verifier() { |
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306 |
if (_activated) Thread::current()->_allow_allocation_count--; |
|
307 |
} |
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308 |
#else |
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309 |
No_Alloc_Verifier(bool activated = true) {} |
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310 |
~No_Alloc_Verifier() {} |
|
311 |
#endif |
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312 |
}; |