DoubleBufferQueue.h

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/*
 Copyright (2016) Michael Baer, Daniel Bonrath, 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.
 */

#ifndef __M2ETIS_UTIL_DOUBLEBUFFERQUEUE_H__
#define __M2ETIS_UTIL_DOUBLEBUFFERQUEUE_H__

#include <queue>

#include "m2etis/util/Exceptions.h"

#include "boost/thread/recursive_mutex.hpp"

namespace m2etis {
namespace util {

        template<typename T, bool producer = true, bool consumer = true>
        class DoubleBufferQueue {
        public:
                DoubleBufferQueue() : _queueA(), _queueB(), _queueRead(&_queueA), _queueWrite(&_queueB), _lock() {
                }

                void push(const T & value) {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        _queueWrite->push(value);
                        assert(!empty());
                }

                void pop() {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                M2ETIS_THROW_API("DoubleBufferQueue", "nothing to pop");
                        }

                        _queueRead->pop();
                }

                T front() {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                M2ETIS_THROW_API("DoubleBufferQueue", "nothing to get");
                        }

                        return _queueRead->front();
                }

                T poll() {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        if (_queueRead->empty()) {
                                swap();
                        }

                        if (_queueRead->empty()) {
                                M2ETIS_THROW_API("DoubleBufferQueue", "nothing to get");
                        }

                        T ret = _queueRead->front();
                        _queueRead->pop();
                        return ret;
                }

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

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

                void clear() {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        while(!_queueRead->empty()) {
                                _queueRead->pop();
                        }
                        while(!_queueWrite->empty()) {
                                _queueWrite->pop();
                        }
                }

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

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

                boost::recursive_mutex _lock;

                DoubleBufferQueue(const DoubleBufferQueue &);

                void swap() {
                        boost::recursive_mutex::scoped_lock scopeLock(_lock);
                        if (_queueRead == &_queueA) {
                                _queueWrite = &_queueA;
                                _queueRead = &_queueB;
                        } else {
                                _queueWrite = &_queueB;
                                _queueRead = &_queueA;
                        }
                }
        };

} /* namespace util */
} /* namespace m2etis */

#endif /* __M2ETIS_UTIL_DOUBLEBUFFERQUEUE_H__ */