DoubleBufferQueue.h

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/*
 * clockUtils
 * Copyright (2015) Michael Baer, Daniel Bonrath, All rights reserved.
 *
 * This file is part of clockUtils; clockUtils is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef __CLOCKUTILS_CONTAINER_DOUBLEBUFFERQUEUE_H__
#define __CLOCKUTILS_CONTAINER_DOUBLEBUFFERQUEUE_H__

#include <mutex>
#include <queue>

#include "clockUtils/errors.h"

#include "clockUtils/container/containerParameters.h"

namespace clockUtils {
namespace container {

        template<typename T, bool producer = true, bool consumer = true>
        class DoubleBufferQueue {
        private:
                template<bool v>
                struct Bool2Type {
                        enum {
                                value = v
                        };
                };

        public:
                DoubleBufferQueue() : _queueA(), _queueB(), _queueRead(&_queueA), _queueWrite(&_queueB), _readLock(), _writeLock() {
                }

                void push(const T & value) {
                        std::lock_guard<std::mutex> lg(_writeLock);
                        _queueWrite->push(value);
                }

                ClockError pop() {
                        return pop(Bool2Type<consumer>());
                }

                ClockError front(T & value) {
                        return front(Bool2Type<consumer>(), value);
                }

                ClockError poll(T & value) {
                        return poll(Bool2Type<consumer>(), value);
                }

                inline bool empty() const {
                        return _queueRead->empty() && _queueWrite->empty();
                }

                inline size_t size() const {
                        return _queueRead->size() + _queueWrite->size();
                }

                void clear() {
                        _readLock.lock();
                        while (!_queueRead->empty()) {
                                _queueRead->pop();
                        }
                        _readLock.unlock();
                        _writeLock.lock();
                        while (!_queueWrite->empty()) {
                                _queueWrite->pop();
                        }
                        _writeLock.unlock();
                }

        private:
                std::queue<T> _queueA;
                std::queue<T> _queueB;

                std::queue<T> * _queueRead;
                std::queue<T> * _queueWrite;

                std::mutex _readLock;
                std::mutex _writeLock;

                ClockError pop(Bool2Type<true>) {
                        static_assert(consumer, "Consumer must be true here");
                        std::lock_guard<std::mutex> lg(_readLock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                _queueRead->pop();
                                return ClockError::SUCCESS;
                        }
                }

                ClockError pop(Bool2Type<false>) {
                        static_assert(!consumer, "Consumer must be false here");
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                _queueRead->pop();
                                return ClockError::SUCCESS;
                        }
                }

                ClockError front(Bool2Type<true>, T & value) {
                        static_assert(consumer, "Consumer must be true here");
                        std::lock_guard<std::mutex> lg(_readLock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                value = _queueRead->front();
                                return ClockError::SUCCESS;
                        }
                }

                ClockError front(Bool2Type<false>, T & value) {
                        static_assert(!consumer, "Consumer must be false here");
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                value = _queueRead->front();
                                return ClockError::SUCCESS;
                        }
                }

                ClockError poll(Bool2Type<true>, T & value) {
                        static_assert(consumer, "Consumer must be true here");
                        std::lock_guard<std::mutex> lg(_readLock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                value = _queueRead->front();
                                _queueRead->pop();
                                return ClockError::SUCCESS;
                        }
                }

                ClockError poll(Bool2Type<false>, T & value) {
                        static_assert(!consumer, "Consumer must be false here");
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                return ClockError::NO_ELEMENT;
                        } else {
                                value = _queueRead->front();
                                _queueRead->pop();
                                return ClockError::SUCCESS;
                        }
                }

                void swap() {
                        std::lock_guard<std::mutex> lg(_writeLock);
                        if (_queueRead == &_queueA) {
                                _queueWrite = &_queueA;
                                _queueRead = &_queueB;
                        } else {
                                _queueWrite = &_queueB;
                                _queueRead = &_queueA;
                        }
                }

                DoubleBufferQueue(const DoubleBufferQueue &) = delete;
        };

} /* namespace container */
} /* namespace clockUtils */

#endif /* __CLOCKUTILS_CONTAINER_DOUBLEBUFFERQUEUE_H__ */