// Copyright 2017 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_HEAP_BARRIER_H_
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#define V8_HEAP_BARRIER_H_
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#include "src/base/platform/condition-variable.h"
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#include "src/base/platform/mutex.h"
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namespace v8 {
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namespace internal {
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// Barrier that can be used once to synchronize a dynamic number of tasks
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// working concurrently.
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//
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// Usage:
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// void RunConcurrently(OneShotBarrier* shared_barrier) {
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// shared_barrier->Start();
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// do {
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// {
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// /* process work and create new work */
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// barrier->NotifyAll();
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// /* process work and create new work */
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// }
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// } while(!shared_barrier->Wait());
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// }
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//
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// Note: If Start() is not called in time, e.g., because the first concurrent
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// task is already done processing all work, then Done() will return true
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// immediately.
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class OneshotBarrier {
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public:
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OneshotBarrier() : tasks_(0), waiting_(0), done_(false) {}
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void Start() {
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base::LockGuard<base::Mutex> guard(&mutex_);
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tasks_++;
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}
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void NotifyAll() {
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base::LockGuard<base::Mutex> guard(&mutex_);
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if (waiting_ > 0) condition_.NotifyAll();
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}
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bool Wait() {
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base::LockGuard<base::Mutex> guard(&mutex_);
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if (done_) return true;
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DCHECK_LE(waiting_, tasks_);
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waiting_++;
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if (waiting_ == tasks_) {
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done_ = true;
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condition_.NotifyAll();
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} else {
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// Spurious wakeup is ok here.
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condition_.Wait(&mutex_);
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}
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waiting_--;
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return done_;
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}
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// Only valid to be called in a sequential setting.
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bool DoneForTesting() const { return done_; }
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private:
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base::ConditionVariable condition_;
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base::Mutex mutex_;
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int tasks_;
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int waiting_;
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bool done_;
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};
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} // namespace internal
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} // namespace v8
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#endif // V8_HEAP_BARRIER_H_
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