ProducerConsumerQueue.h

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/*
 * This file is part of the TrinityCore Project. See AUTHORS file for Copyright information
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef TRINITY_PRODUCER_CONSUMER_QUEUE_H
#define TRINITY_PRODUCER_CONSUMER_QUEUE_H
 
#include <condition_variable>
#include <mutex>
#include <queue>
#include <atomic>
#include <type_traits>
 
template <typename T>
class ProducerConsumerQueue
{
private:
 mutable std::mutex _queueLock;
 std::queue<T> _queue;
 std::condition_variable _condition;
 std::atomic<bool> _shutdown;
 
public:
 
 ProducerConsumerQueue() : _shutdown(false) { }
 
 void Push(T const& value)
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 _queue.push(value);
 
 _condition.notify_one();
 }
 
 void Push(T&& value)
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 _queue.push(std::move(value));
 
 _condition.notify_one();
 }
 
 bool Empty() const
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 
 return _queue.empty();
 }
 
 size_t Size() const
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 
 return _queue.size();
 }
 
 bool Pop(T& value)
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 
 if (_queue.empty() || _shutdown)
 return false;
 
 value = std::move(_queue.front());
 
 _queue.pop();
 
 return true;
 }
 
 void WaitAndPop(T& value)
 {
 std::unique_lock<std::mutex> lock(_queueLock);
 
 // we could be using .wait(lock, predicate) overload here but it is broken
 // https://connect.microsoft.com/VisualStudio/feedback/details/1098841
 while (_queue.empty() && !_shutdown)
 _condition.wait(lock);
 
 if (_queue.empty() || _shutdown)
 return;
 
 value = _queue.front();
 
 _queue.pop();
 }
 
 void Cancel()
 {
 std::unique_lock<std::mutex> lock(_queueLock);
 
 while (!_queue.empty())
 {
 T& value = _queue.front();
 
 if constexpr (std::is_pointer_v<T>)
 delete value;
 
 _queue.pop();
 }
 
 _shutdown = true;
 
 _condition.notify_all();
 }
};
 
#endif // TRINITY_PRODUCER_CONSUMER_QUEUE_H