| /* |
| * Copyright (c) 1997, 2015, 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. |
| * |
| */ |
| |
| #ifndef SHARE_VM_GC_SHARED_GCLOCKER_HPP |
| #define SHARE_VM_GC_SHARED_GCLOCKER_HPP |
| |
| #include "gc/shared/collectedHeap.hpp" |
| #include "gc/shared/genCollectedHeap.hpp" |
| #include "memory/universe.hpp" |
| #include "oops/oop.hpp" |
| |
| // The direct lock/unlock calls do not force a collection if an unlock |
| // decrements the count to zero. Avoid calling these if at all possible. |
| |
| class GCLocker: public AllStatic { |
| private: |
| // The _jni_lock_count keeps track of the number of threads that are |
| // currently in a critical region. It's only kept up to date when |
| // _needs_gc is true. The current value is computed during |
| // safepointing and decremented during the slow path of GCLocker |
| // unlocking. |
| static volatile jint _jni_lock_count; // number of jni active instances. |
| static volatile bool _needs_gc; // heap is filling, we need a GC |
| // note: bool is typedef'd as jint |
| static volatile bool _doing_gc; // unlock_critical() is doing a GC |
| |
| #ifdef ASSERT |
| // This lock count is updated for all operations and is used to |
| // validate the jni_lock_count that is computed during safepoints. |
| static volatile jint _debug_jni_lock_count; |
| #endif |
| |
| // At a safepoint, visit all threads and count the number of active |
| // critical sections. This is used to ensure that all active |
| // critical sections are exited before a new one is started. |
| static void verify_critical_count() NOT_DEBUG_RETURN; |
| |
| static void jni_lock(JavaThread* thread); |
| static void jni_unlock(JavaThread* thread); |
| |
| static bool is_active_internal() { |
| verify_critical_count(); |
| return _jni_lock_count > 0; |
| } |
| |
| static void log_debug_jni(const char* msg); |
| public: |
| // Accessors |
| static bool is_active() { |
| assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint"); |
| return is_active_internal(); |
| } |
| static bool needs_gc() { return _needs_gc; } |
| |
| // Shorthand |
| static bool is_active_and_needs_gc() { |
| // Use is_active_internal since _needs_gc can change from true to |
| // false outside of a safepoint, triggering the assert in |
| // is_active. |
| return needs_gc() && is_active_internal(); |
| } |
| |
| // In debug mode track the locking state at all times |
| static void increment_debug_jni_lock_count() NOT_DEBUG_RETURN; |
| static void decrement_debug_jni_lock_count() NOT_DEBUG_RETURN; |
| |
| // Set the current lock count |
| static void set_jni_lock_count(int count) { |
| _jni_lock_count = count; |
| verify_critical_count(); |
| } |
| |
| // Sets _needs_gc if is_active() is true. Returns is_active(). |
| static bool check_active_before_gc(); |
| |
| // Stalls the caller (who should not be in a jni critical section) |
| // until needs_gc() clears. Note however that needs_gc() may be |
| // set at a subsequent safepoint and/or cleared under the |
| // JNICritical_lock, so the caller may not safely assert upon |
| // return from this method that "!needs_gc()" since that is |
| // not a stable predicate. |
| static void stall_until_clear(); |
| |
| // The following two methods are used for JNI critical regions. |
| // If we find that we failed to perform a GC because the GCLocker |
| // was active, arrange for one as soon as possible by allowing |
| // all threads in critical regions to complete, but not allowing |
| // other critical regions to be entered. The reasons for that are: |
| // 1) a GC request won't be starved by overlapping JNI critical |
| // region activities, which can cause unnecessary OutOfMemory errors. |
| // 2) even if allocation requests can still be satisfied before GC locker |
| // becomes inactive, for example, in tenured generation possibly with |
| // heap expansion, those allocations can trigger lots of safepointing |
| // attempts (ineffective GC attempts) and require Heap_lock which |
| // slow down allocations tremendously. |
| // |
| // Note that critical regions can be nested in a single thread, so |
| // we must allow threads already in critical regions to continue. |
| // |
| // JNI critical regions are the only participants in this scheme |
| // because they are, by spec, well bounded while in a critical region. |
| // |
| // Each of the following two method is split into a fast path and a |
| // slow path. JNICritical_lock is only grabbed in the slow path. |
| // _needs_gc is initially false and every java thread will go |
| // through the fast path, which simply increments or decrements the |
| // current thread's critical count. When GC happens at a safepoint, |
| // GCLocker::is_active() is checked. Since there is no safepoint in |
| // the fast path of lock_critical() and unlock_critical(), there is |
| // no race condition between the fast path and GC. After _needs_gc |
| // is set at a safepoint, every thread will go through the slow path |
| // after the safepoint. Since after a safepoint, each of the |
| // following two methods is either entered from the method entry and |
| // falls into the slow path, or is resumed from the safepoints in |
| // the method, which only exist in the slow path. So when _needs_gc |
| // is set, the slow path is always taken, till _needs_gc is cleared. |
| static void lock_critical(JavaThread* thread); |
| static void unlock_critical(JavaThread* thread); |
| |
| static address needs_gc_address() { return (address) &_needs_gc; } |
| }; |
| |
| |
| // A NoGCVerifier object can be placed in methods where one assumes that |
| // no garbage collection will occur. The destructor will verify this property |
| // unless the constructor is called with argument false (not verifygc). |
| // |
| // The check will only be done in debug mode and if verifygc true. |
| |
| class NoGCVerifier: public StackObj { |
| friend class PauseNoGCVerifier; |
| |
| protected: |
| bool _verifygc; |
| unsigned int _old_invocations; |
| |
| public: |
| #ifdef ASSERT |
| NoGCVerifier(bool verifygc = true); |
| ~NoGCVerifier(); |
| #else |
| NoGCVerifier(bool verifygc = true) {} |
| ~NoGCVerifier() {} |
| #endif |
| }; |
| |
| // A PauseNoGCVerifier is used to temporarily pause the behavior |
| // of a NoGCVerifier object. If we are not in debug mode or if the |
| // NoGCVerifier object has a _verifygc value of false, then there |
| // is nothing to do. |
| |
| class PauseNoGCVerifier: public StackObj { |
| private: |
| NoGCVerifier * _ngcv; |
| |
| public: |
| #ifdef ASSERT |
| PauseNoGCVerifier(NoGCVerifier * ngcv); |
| ~PauseNoGCVerifier(); |
| #else |
| PauseNoGCVerifier(NoGCVerifier * ngcv) {} |
| ~PauseNoGCVerifier() {} |
| #endif |
| }; |
| |
| |
| // A NoSafepointVerifier object will throw an assertion failure if |
| // the current thread passes a possible safepoint while this object is |
| // instantiated. A safepoint, will either be: an oop allocation, blocking |
| // on a Mutex or JavaLock, or executing a VM operation. |
| // |
| // If StrictSafepointChecks is turned off, it degrades into a NoGCVerifier |
| // |
| class NoSafepointVerifier : public NoGCVerifier { |
| friend class PauseNoSafepointVerifier; |
| |
| private: |
| bool _activated; |
| Thread *_thread; |
| public: |
| #ifdef ASSERT |
| NoSafepointVerifier(bool activated = true, bool verifygc = true ) : |
| NoGCVerifier(verifygc), |
| _activated(activated) { |
| _thread = Thread::current(); |
| if (_activated) { |
| _thread->_allow_allocation_count++; |
| _thread->_allow_safepoint_count++; |
| } |
| } |
| |
| ~NoSafepointVerifier() { |
| if (_activated) { |
| _thread->_allow_allocation_count--; |
| _thread->_allow_safepoint_count--; |
| } |
| } |
| #else |
| NoSafepointVerifier(bool activated = true, bool verifygc = true) : NoGCVerifier(verifygc){} |
| ~NoSafepointVerifier() {} |
| #endif |
| }; |
| |
| // A PauseNoSafepointVerifier is used to temporarily pause the |
| // behavior of a NoSafepointVerifier object. If we are not in debug |
| // mode then there is nothing to do. If the NoSafepointVerifier |
| // object has an _activated value of false, then there is nothing to |
| // do for safepoint and allocation checking, but there may still be |
| // something to do for the underlying NoGCVerifier object. |
| |
| class PauseNoSafepointVerifier : public PauseNoGCVerifier { |
| private: |
| NoSafepointVerifier * _nsv; |
| |
| public: |
| #ifdef ASSERT |
| PauseNoSafepointVerifier(NoSafepointVerifier * nsv) |
| : PauseNoGCVerifier(nsv) { |
| |
| _nsv = nsv; |
| if (_nsv->_activated) { |
| _nsv->_thread->_allow_allocation_count--; |
| _nsv->_thread->_allow_safepoint_count--; |
| } |
| } |
| |
| ~PauseNoSafepointVerifier() { |
| if (_nsv->_activated) { |
| _nsv->_thread->_allow_allocation_count++; |
| _nsv->_thread->_allow_safepoint_count++; |
| } |
| } |
| #else |
| PauseNoSafepointVerifier(NoSafepointVerifier * nsv) |
| : PauseNoGCVerifier(nsv) {} |
| ~PauseNoSafepointVerifier() {} |
| #endif |
| }; |
| |
| // A SkipGCALot object is used to elide the usual effect of gc-a-lot |
| // over a section of execution by a thread. Currently, it's used only to |
| // prevent re-entrant calls to GC. |
| class SkipGCALot : public StackObj { |
| private: |
| bool _saved; |
| Thread* _t; |
| |
| public: |
| #ifdef ASSERT |
| SkipGCALot(Thread* t) : _t(t) { |
| _saved = _t->skip_gcalot(); |
| _t->set_skip_gcalot(true); |
| } |
| |
| ~SkipGCALot() { |
| assert(_t->skip_gcalot(), "Save-restore protocol invariant"); |
| _t->set_skip_gcalot(_saved); |
| } |
| #else |
| SkipGCALot(Thread* t) { } |
| ~SkipGCALot() { } |
| #endif |
| }; |
| |
| // JRT_LEAF currently can be called from either _thread_in_Java or |
| // _thread_in_native mode. In _thread_in_native, it is ok |
| // for another thread to trigger GC. The rest of the JRT_LEAF |
| // rules apply. |
| class JRTLeafVerifier : public NoSafepointVerifier { |
| static bool should_verify_GC(); |
| public: |
| #ifdef ASSERT |
| JRTLeafVerifier(); |
| ~JRTLeafVerifier(); |
| #else |
| JRTLeafVerifier() {} |
| ~JRTLeafVerifier() {} |
| #endif |
| }; |
| |
| // A NoAllocVerifier object can be placed in methods where one assumes that |
| // no allocation will occur. The destructor will verify this property |
| // unless the constructor is called with argument false (not activated). |
| // |
| // The check will only be done in debug mode and if activated. |
| // Note: this only makes sense at safepoints (otherwise, other threads may |
| // allocate concurrently.) |
| |
| class NoAllocVerifier : public StackObj { |
| private: |
| bool _activated; |
| |
| public: |
| #ifdef ASSERT |
| NoAllocVerifier(bool activated = true) { |
| _activated = activated; |
| if (_activated) Thread::current()->_allow_allocation_count++; |
| } |
| |
| ~NoAllocVerifier() { |
| if (_activated) Thread::current()->_allow_allocation_count--; |
| } |
| #else |
| NoAllocVerifier(bool activated = true) {} |
| ~NoAllocVerifier() {} |
| #endif |
| }; |
| |
| #endif // SHARE_VM_GC_SHARED_GCLOCKER_HPP |