| // Copyright 2019 The SwiftShader Authors. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // This file contains a number of synchronization primitives for concurrency. |
| // |
| // You may be tempted to change this code to unlock the mutex before calling |
| // std::condition_variable::notify_[one,all]. Please read |
| // https://issuetracker.google.com/issues/133135427 before making this sort of |
| // change. |
| |
| #ifndef sw_Synchronization_hpp |
| #define sw_Synchronization_hpp |
| |
| #include <assert.h> |
| #include <chrono> |
| #include <condition_variable> |
| #include <mutex> |
| #include <queue> |
| |
| namespace sw { |
| |
| // TaskEvents is an interface for notifying when tasks begin and end. |
| // Tasks can be nested and/or overlapping. |
| // TaskEvents is used for task queue synchronization. |
| class TaskEvents |
| { |
| public: |
| // start() is called before a task begins. |
| virtual void start() = 0; |
| // finish() is called after a task ends. finish() must only be called after |
| // a corresponding call to start(). |
| virtual void finish() = 0; |
| // complete() is a helper for calling start() followed by finish(). |
| inline void complete() |
| { |
| start(); |
| finish(); |
| } |
| |
| protected: |
| virtual ~TaskEvents() = default; |
| }; |
| |
| // WaitGroup is a synchronization primitive that allows you to wait for |
| // collection of asynchronous tasks to finish executing. |
| // Call add() before each task begins, and then call done() when after each task |
| // is finished. |
| // At the same time, wait() can be used to block until all tasks have finished. |
| // WaitGroup takes its name after Golang's sync.WaitGroup. |
| class WaitGroup : public TaskEvents |
| { |
| public: |
| // add() begins a new task. |
| void add() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| ++count_; |
| } |
| |
| // done() is called when a task of the WaitGroup has been completed. |
| // Returns true if there are no more tasks currently running in the |
| // WaitGroup. |
| bool done() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| assert(count_ > 0); |
| --count_; |
| if(count_ == 0) |
| { |
| condition.notify_all(); |
| } |
| return count_ == 0; |
| } |
| |
| // wait() blocks until all the tasks have been finished. |
| void wait() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| condition.wait(lock, [this] { return count_ == 0; }); |
| } |
| |
| // wait() blocks until all the tasks have been finished or the timeout |
| // has been reached, returning true if all tasks have been completed, or |
| // false if the timeout has been reached. |
| template<class CLOCK, class DURATION> |
| bool wait(const std::chrono::time_point<CLOCK, DURATION> &timeout) |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| return condition.wait_until(lock, timeout, [this] { return count_ == 0; }); |
| } |
| |
| // count() returns the number of times add() has been called without a call |
| // to done(). |
| // Note: No lock is held after count() returns, so the count may immediately |
| // change after returning. |
| int32_t count() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| return count_; |
| } |
| |
| // TaskEvents compliance |
| void start() override { add(); } |
| void finish() override { done(); } |
| |
| private: |
| int32_t count_ = 0; // guarded by mutex |
| std::mutex mutex; |
| std::condition_variable condition; |
| }; |
| |
| // Chan is a thread-safe FIFO queue of type T. |
| // Chan takes its name after Golang's chan. |
| template<typename T> |
| class Chan |
| { |
| public: |
| Chan(); |
| |
| // take returns the next item in the chan, blocking until an item is |
| // available. |
| T take(); |
| |
| // tryTake returns a <T, bool> pair. |
| // If the chan is not empty, then the next item and true are returned. |
| // If the chan is empty, then a default-initialized T and false are returned. |
| std::pair<T, bool> tryTake(); |
| |
| // put places an item into the chan, blocking if the chan is bounded and |
| // full. |
| void put(const T &v); |
| |
| // Returns the number of items in the chan. |
| // Note: that this may change as soon as the function returns, so should |
| // only be used for debugging. |
| size_t count(); |
| |
| private: |
| std::queue<T> queue; |
| std::mutex mutex; |
| std::condition_variable added; |
| }; |
| |
| template<typename T> |
| Chan<T>::Chan() |
| {} |
| |
| template<typename T> |
| T Chan<T>::take() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| // Wait for item to be added. |
| added.wait(lock, [this] { return queue.size() > 0; }); |
| T out = queue.front(); |
| queue.pop(); |
| return out; |
| } |
| |
| template<typename T> |
| std::pair<T, bool> Chan<T>::tryTake() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| if(queue.size() == 0) |
| { |
| return std::make_pair(T{}, false); |
| } |
| T out = queue.front(); |
| queue.pop(); |
| return std::make_pair(out, true); |
| } |
| |
| template<typename T> |
| void Chan<T>::put(const T &item) |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| queue.push(item); |
| added.notify_one(); |
| } |
| |
| template<typename T> |
| size_t Chan<T>::count() |
| { |
| std::unique_lock<std::mutex> lock(mutex); |
| return queue.size(); |
| } |
| |
| } // namespace sw |
| |
| #endif // sw_Synchronization_hpp |