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