// 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_