| // Copyright 2016 Google Inc. 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. |
| |
| // Module Overview: Starboard Queue module |
| // |
| // Defines a C++-only synchronized queue implementation, built entirely on top |
| // of Starboard synchronization primitives. It can be safely used by both |
| // clients and implementations. |
| |
| #ifndef STARBOARD_QUEUE_H_ |
| #define STARBOARD_QUEUE_H_ |
| |
| #include <deque> |
| |
| #include "starboard/condition_variable.h" |
| #include "starboard/export.h" |
| #include "starboard/mutex.h" |
| #include "starboard/time.h" |
| #include "starboard/types.h" |
| |
| #ifndef __cplusplus |
| #error "Only C++ files can include this header." |
| #endif |
| |
| namespace starboard { |
| |
| // Synchronized, blocking queue, based on starboard::ConditionVariable. This |
| // class is designed for T to be a pointer type, or something otherwise |
| // inherently Nullable, as there is no way to distinguish T() from "no result." |
| template <typename T> |
| class Queue { |
| public: |
| Queue() : condition_(mutex_), wake_(false) {} |
| ~Queue() {} |
| |
| // Polls for an item, returning the default value of T if nothing is present. |
| T Poll() { |
| ScopedLock lock(mutex_); |
| if (!queue_.empty()) { |
| T entry = queue_.front(); |
| queue_.pop_front(); |
| return entry; |
| } |
| |
| return T(); |
| } |
| |
| // Gets the item at the front of the queue, blocking until there is such an |
| // item, or the queue is woken up. If there are multiple waiters, this Queue |
| // guarantees that only one waiter will receive any given queue item. |
| T Get() { |
| ScopedLock lock(mutex_); |
| while (queue_.empty()) { |
| if (wake_) { |
| wake_ = false; |
| return T(); |
| } |
| |
| condition_.Wait(); |
| } |
| |
| T entry = queue_.front(); |
| queue_.pop_front(); |
| return entry; |
| } |
| |
| // Gets the item at the front of the queue, blocking until there is such an |
| // item, or the given timeout duration expires, or the queue is woken up. If |
| // there are multiple waiters, this Queue guarantees that only one waiter will |
| // receive any given queue item. |
| T GetTimed(SbTime duration) { |
| ScopedLock lock(mutex_); |
| SbTimeMonotonic start = SbTimeGetMonotonicNow(); |
| while (queue_.empty()) { |
| if (wake_) { |
| wake_ = false; |
| return T(); |
| } |
| |
| SbTimeMonotonic elapsed = SbTimeGetMonotonicNow() - start; |
| if (elapsed >= duration) { |
| return T(); |
| } |
| condition_.WaitTimed(duration - elapsed); |
| } |
| |
| T entry = queue_.front(); |
| queue_.pop_front(); |
| return entry; |
| } |
| |
| // Pushes |value| onto the back of the queue, waking up a single waiter, if |
| // any exist. |
| void Put(T value) { |
| ScopedLock lock(mutex_); |
| queue_.push_back(value); |
| condition_.Signal(); |
| } |
| |
| // Forces one waiter to wake up empty-handed. |
| void Wake() { |
| ScopedLock lock(mutex_); |
| wake_ = true; |
| condition_.Signal(); |
| } |
| |
| private: |
| Mutex mutex_; |
| ConditionVariable condition_; |
| std::deque<T> queue_; |
| bool wake_; |
| }; |
| |
| } // namespace starboard |
| |
| #endif // STARBOARD_QUEUE_H_ |