127 lines
5.0 KiB
C++
127 lines
5.0 KiB
C++
/*
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* Copyright (c) 2018, 2019, Red Hat, Inc. 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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#include "precompiled.hpp"
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#include "gc/shenandoah/shenandoahHeap.hpp"
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#include "gc/shenandoah/shenandoahUtils.hpp"
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#include "gc/shenandoah/shenandoahEvacOOMHandler.hpp"
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#include "gc/shenandoah/shenandoahThreadLocalData.hpp"
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#include "runtime/atomic.hpp"
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#include "runtime/os.hpp"
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#include "runtime/thread.hpp"
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const jint ShenandoahEvacOOMHandler::OOM_MARKER_MASK = 0x80000000;
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ShenandoahEvacOOMHandler::ShenandoahEvacOOMHandler() :
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_threads_in_evac(0) {
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}
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void ShenandoahEvacOOMHandler::wait_for_no_evac_threads() {
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while ((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) != 0) {
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os::naked_short_sleep(1);
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}
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// At this point we are sure that no threads can evacuate anything. Raise
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// the thread-local oom_during_evac flag to indicate that any attempt
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// to evacuate should simply return the forwarding pointer instead (which is safe now).
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ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), true);
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}
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void ShenandoahEvacOOMHandler::enter_evacuation() {
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jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
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assert(!ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
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assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
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if ((threads_in_evac & OOM_MARKER_MASK) != 0) {
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wait_for_no_evac_threads();
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return;
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}
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while (true) {
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jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, threads_in_evac + 1);
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if (other == threads_in_evac) {
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// Success: caller may safely enter evacuation
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DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), true));
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return;
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} else {
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// Failure:
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// - if offender has OOM_MARKER_MASK, then loop until no more threads in evac
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// - otherwise re-try CAS
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if ((other & OOM_MARKER_MASK) != 0) {
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wait_for_no_evac_threads();
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return;
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}
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threads_in_evac = other;
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}
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}
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}
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void ShenandoahEvacOOMHandler::leave_evacuation() {
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if (!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current())) {
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assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) > 0, "sanity");
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// NOTE: It's ok to simply decrement, even with mask set, because unmasked value is positive.
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Atomic::dec(&_threads_in_evac);
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} else {
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// If we get here, the current thread has already gone through the
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// OOM-during-evac protocol and has thus either never entered or successfully left
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// the evacuation region. Simply flip its TL oom-during-evac flag back off.
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ShenandoahThreadLocalData::set_oom_during_evac(Thread::current(), false);
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}
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DEBUG_ONLY(ShenandoahThreadLocalData::set_evac_allowed(Thread::current(), false));
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assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must be turned off");
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}
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void ShenandoahEvacOOMHandler::handle_out_of_memory_during_evacuation() {
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assert(ShenandoahThreadLocalData::is_evac_allowed(Thread::current()), "sanity");
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assert(!ShenandoahThreadLocalData::is_oom_during_evac(Thread::current()), "TL oom-during-evac must not be set");
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jint threads_in_evac = Atomic::load_acquire(&_threads_in_evac);
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while (true) {
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jint other = Atomic::cmpxchg(&_threads_in_evac, threads_in_evac, (threads_in_evac - 1) | OOM_MARKER_MASK);
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if (other == threads_in_evac) {
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// Success: wait for other threads to get out of the protocol and return.
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wait_for_no_evac_threads();
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return;
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} else {
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// Failure: try again with updated new value.
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threads_in_evac = other;
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}
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}
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}
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void ShenandoahEvacOOMHandler::clear() {
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assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at a safepoint");
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assert((Atomic::load_acquire(&_threads_in_evac) & ~OOM_MARKER_MASK) == 0, "sanity");
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Atomic::release_store_fence(&_threads_in_evac, (jint)0);
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}
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ShenandoahEvacOOMScope::ShenandoahEvacOOMScope() {
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ShenandoahHeap::heap()->enter_evacuation();
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}
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ShenandoahEvacOOMScope::~ShenandoahEvacOOMScope() {
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ShenandoahHeap::heap()->leave_evacuation();
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}
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