154a1a02bf
Use script and some manual fixup to fix directores names in include guards. Reviewed-by: lfoltan, eosterlund, kbarrett
149 lines
6.2 KiB
C++
149 lines
6.2 KiB
C++
/*
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* Copyright (c) 1997, 2019, 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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#ifndef SHARE_GC_SHARED_GCLOCKER_HPP
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#define SHARE_GC_SHARED_GCLOCKER_HPP
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#include "memory/allocation.hpp"
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#include "utilities/globalDefinitions.hpp"
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#include "utilities/macros.hpp"
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class JavaThread;
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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 GCLocker: public AllStatic {
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private:
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// The _jni_lock_count keeps track of the number of threads that are
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// currently in a critical region. It's only kept up to date when
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// _needs_gc is true. The current value is computed during
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// safepointing and decremented during the slow path of GCLocker
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// unlocking.
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static volatile jint _jni_lock_count; // number of jni 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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#ifdef ASSERT
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// This lock count is updated for all operations and is used to
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// validate the jni_lock_count that is computed during safepoints.
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static volatile jint _debug_jni_lock_count;
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#endif
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// At a safepoint, visit all threads and count the number of active
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// critical sections. This is used to ensure that all active
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// critical sections are exited before a new one is started.
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static void verify_critical_count() NOT_DEBUG_RETURN;
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static void jni_lock(JavaThread* thread);
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static void jni_unlock(JavaThread* thread);
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static bool is_active_internal() {
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verify_critical_count();
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return _jni_lock_count > 0;
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}
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static void log_debug_jni(const char* msg);
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static bool is_at_safepoint();
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public:
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// Accessors
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static bool is_active() {
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assert(GCLocker::is_at_safepoint(), "only read at safepoint");
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return is_active_internal();
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}
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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() {
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// Use is_active_internal since _needs_gc can change from true to
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// false outside of a safepoint, triggering the assert in
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// is_active.
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return needs_gc() && is_active_internal();
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}
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// In debug mode track the locking state at all times
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static void increment_debug_jni_lock_count() NOT_DEBUG_RETURN;
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static void decrement_debug_jni_lock_count() NOT_DEBUG_RETURN;
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// Set the current lock count
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static void set_jni_lock_count(int count) {
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_jni_lock_count = count;
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verify_critical_count();
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}
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// Sets _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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// 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 GCLocker
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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
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// slow 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 simply increments or decrements the
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// current thread's critical count. When GC happens at a safepoint,
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// GCLocker::is_active() is checked. Since there is no safepoint in
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// the fast path of lock_critical() and unlock_critical(), there is
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// no race condition between the fast path and GC. After _needs_gc
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// is set at a safepoint, every thread will go through the slow path
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// after the safepoint. Since after a safepoint, each of the
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// following two methods is either entered from the method entry and
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// falls into the slow path, or is resumed from the safepoints in
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// the method, which only exist in the slow path. So when _needs_gc
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// is set, the slow path is always taken, till _needs_gc is cleared.
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inline static void lock_critical(JavaThread* thread);
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inline static void unlock_critical(JavaThread* thread);
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static address needs_gc_address() { return (address) &_needs_gc; }
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};
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#endif // SHARE_GC_SHARED_GCLOCKER_HPP
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