ProducerConsumerQueue.h

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/*
 * Copyright (C) 2008-2016 TrinityCore <http://www.trinitycore.org/>
 *
 * 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 _PCQ_H
#define _PCQ_H

#include <condition_variable>
#include <mutex>
#include <queue>
#include <atomic>
#include <type_traits>

template <typename T>
class ProducerConsumerQueue
{
private:
 std::mutex _queueLock;
 std::queue<T> _queue;
 std::condition_variable _condition;
 std::atomic<bool> _shutdown;

public:

 ProducerConsumerQueue<T>() : _shutdown(false) { }

 void Push(const T& value)
 {
 std::lock_guard<std::mutex> lock(_queueLock);
 _queue.push(std::move(value));

 _condition.notify_one();
 }

 bool Empty()
 {
 std::lock_guard<std::mutex> lock(_queueLock);

 return _queue.empty();
 }

 bool Pop(T& value)
 {
 std::lock_guard<std::mutex> lock(_queueLock);

 if (_queue.empty() || _shutdown)
 return false;

 value = _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();

 DeleteQueuedObject(value);

 _queue.pop();
 }

 _shutdown = true;

 _condition.notify_all();
 }

private:
 template<typename E = T>
 typename std::enable_if<std::is_pointer<E>::value>::type DeleteQueuedObject(E& obj) { delete obj; }

 template<typename E = T>
 typename std::enable_if<!std::is_pointer<E>::value>::type DeleteQueuedObject(E const& /*packet*/) { }
};

#endif