135 lines
5.0 KiB
C++
135 lines
5.0 KiB
C++
/*
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* Copyright (c) 2014, 2016, 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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#include "precompiled.hpp"
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#include "gc/g1/suspendibleThreadSet.hpp"
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#include "runtime/mutexLocker.hpp"
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#include "runtime/semaphore.hpp"
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#include "runtime/thread.inline.hpp"
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uint SuspendibleThreadSet::_nthreads = 0;
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uint SuspendibleThreadSet::_nthreads_stopped = 0;
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bool SuspendibleThreadSet::_suspend_all = false;
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double SuspendibleThreadSet::_suspend_all_start = 0.0;
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static Semaphore* _synchronize_wakeup = NULL;
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void SuspendibleThreadSet_init() {
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assert(_synchronize_wakeup == NULL, "STS already initialized");
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_synchronize_wakeup = new Semaphore();
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}
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bool SuspendibleThreadSet::is_synchronized() {
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assert_lock_strong(STS_lock);
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assert(_nthreads_stopped <= _nthreads, "invariant");
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return _nthreads_stopped == _nthreads;
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}
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void SuspendibleThreadSet::join() {
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assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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while (_suspend_all) {
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ml.wait(Mutex::_no_safepoint_check_flag);
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}
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_nthreads++;
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DEBUG_ONLY(Thread::current()->set_suspendible_thread();)
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}
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void SuspendibleThreadSet::leave() {
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assert(Thread::current()->is_suspendible_thread(), "Thread not joined");
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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assert(_nthreads > 0, "Invalid");
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DEBUG_ONLY(Thread::current()->clear_suspendible_thread();)
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_nthreads--;
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if (_suspend_all && is_synchronized()) {
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// This leave completes a request, so inform the requestor.
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_synchronize_wakeup->signal();
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}
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}
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void SuspendibleThreadSet::yield() {
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assert(Thread::current()->is_suspendible_thread(), "Must have joined");
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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if (_suspend_all) {
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_nthreads_stopped++;
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if (is_synchronized()) {
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if (ConcGCYieldTimeout > 0) {
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double now = os::elapsedTime();
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guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay");
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}
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// This yield completes the request, so inform the requestor.
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_synchronize_wakeup->signal();
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}
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while (_suspend_all) {
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ml.wait(Mutex::_no_safepoint_check_flag);
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}
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assert(_nthreads_stopped > 0, "Invalid");
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_nthreads_stopped--;
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}
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}
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void SuspendibleThreadSet::synchronize() {
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assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
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if (ConcGCYieldTimeout > 0) {
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_suspend_all_start = os::elapsedTime();
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}
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{
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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assert(!_suspend_all, "Only one at a time");
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_suspend_all = true;
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if (is_synchronized()) {
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return;
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}
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} // Release lock before semaphore wait.
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// Semaphore initial count is zero. To reach here, there must be at
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// least one not yielded thread in the set, e.g. is_synchronized()
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// was false before the lock was released. A thread in the set will
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// signal the semaphore iff it is the last to yield or leave while
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// there is an active suspend request. So there will be exactly one
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// signal, which will increment the semaphore count to one, which
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// will then be consumed by this wait, returning it to zero. No
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// thread can exit yield or enter the set until desynchronize is
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// called, so there are no further opportunities for the semaphore
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// being signaled until we get back here again for some later
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// synchronize call. Hence, there is no need to re-check for
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// is_synchronized after the wait; it will always be true there.
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_synchronize_wakeup->wait();
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#ifdef ASSERT
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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assert(_suspend_all, "STS not synchronizing");
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assert(is_synchronized(), "STS not synchronized");
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#endif
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}
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void SuspendibleThreadSet::desynchronize() {
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assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
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MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);
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assert(_suspend_all, "STS not synchronizing");
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assert(is_synchronized(), "STS not synchronized");
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_suspend_all = false;
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ml.notify_all();
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}
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