| // This file is part of Eigen, a lightweight C++ template library | |
| // for linear algebra. | |
| // | |
| // Copyright (C) 2018 Rasmus Munk Larsen <rmlarsen@google.com> | |
| // | |
| // This Source Code Form is subject to the terms of the Mozilla | |
| // Public License v. 2.0. If a copy of the MPL was not distributed | |
| // with this file, You can obtain one at http://mozilla.org/MPL/2.0/. | |
| // Barrier is an object that allows one or more threads to wait until | |
| // Notify has been called a specified number of times. | |
| namespace Eigen { | |
| class Barrier { | |
| public: | |
| Barrier(unsigned int count) : state_(count << 1), notified_(false) { | |
| eigen_plain_assert(((count << 1) >> 1) == count); | |
| } | |
| ~Barrier() { eigen_plain_assert((state_ >> 1) == 0); } | |
| void Notify() { | |
| unsigned int v = state_.fetch_sub(2, std::memory_order_acq_rel) - 2; | |
| if (v != 1) { | |
| // Clear the lowest bit (waiter flag) and check that the original state | |
| // value was not zero. If it was zero, it means that notify was called | |
| // more times than the original count. | |
| eigen_plain_assert(((v + 2) & ~1) != 0); | |
| return; // either count has not dropped to 0, or waiter is not waiting | |
| } | |
| std::unique_lock<std::mutex> l(mu_); | |
| eigen_plain_assert(!notified_); | |
| notified_ = true; | |
| cv_.notify_all(); | |
| } | |
| void Wait() { | |
| unsigned int v = state_.fetch_or(1, std::memory_order_acq_rel); | |
| if ((v >> 1) == 0) return; | |
| std::unique_lock<std::mutex> l(mu_); | |
| while (!notified_) { | |
| cv_.wait(l); | |
| } | |
| } | |
| private: | |
| std::mutex mu_; | |
| std::condition_variable cv_; | |
| std::atomic<unsigned int> state_; // low bit is waiter flag | |
| bool notified_; | |
| }; | |
| // Notification is an object that allows a user to to wait for another | |
| // thread to signal a notification that an event has occurred. | |
| // | |
| // Multiple threads can wait on the same Notification object, | |
| // but only one caller must call Notify() on the object. | |
| struct Notification : Barrier { | |
| Notification() : Barrier(1){}; | |
| }; | |
| } // namespace Eigen | |