Program Listing for File DBQueue.h
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// Copyright 2016 Proyectos y Sistemas de Mantenimiento SL (eProsima).
//
// 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 DBQUEUE_H
#define DBQUEUE_H
#include <queue>
#include <mutex>
#include <memory>
#include <condition_variable>
namespace eprosima {
namespace fastrtps {
template<class T>
class DBQueue
{
public:
DBQueue()
: mForegroundQueue(&mQueueAlpha)
, mBackgroundQueue(&mQueueBeta)
{
}
void Swap()
{
std::unique_lock<std::mutex> fgGuard(mForegroundMutex);
std::unique_lock<std::mutex> bgGuard(mBackgroundMutex);
// Clear the foreground queue.
std::queue<T>().swap(*mForegroundQueue);
auto* swap = mBackgroundQueue;
mBackgroundQueue = mForegroundQueue;
mForegroundQueue = swap;
}
void Push(
const T& item)
{
std::unique_lock<std::mutex> guard(mBackgroundMutex);
mBackgroundQueue->push(item);
}
void Push(
T&& item)
{
std::unique_lock<std::mutex> guard(mBackgroundMutex);
mBackgroundQueue->push(std::move(item));
}
T& Front()
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
return mForegroundQueue->front();
}
const T& Front() const
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
return mForegroundQueue->front();
}
void Pop()
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
mForegroundQueue->pop();
}
T FrontAndPop()
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
// Get value by moving the internal queue reference to a new value
T value = std::move(mForegroundQueue->front());
// At this point mForegroundQueue contains a non valid element, but mutex is taken and next instruction erase it
// Pop value from queue
mForegroundQueue->pop();
// Return value (as it has been created in this scope, it will not be copied but moved or directly forwarded)
return value;
}
bool Empty() const
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
return mForegroundQueue->empty();
}
bool BothEmpty() const
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
std::unique_lock<std::mutex> bgGuard(mBackgroundMutex);
return mForegroundQueue->empty() && mBackgroundQueue->empty();
}
size_t Size() const
{
std::unique_lock<std::mutex> guard(mForegroundMutex);
return mForegroundQueue->size();
}
void Clear()
{
std::unique_lock<std::mutex> fgGuard(mForegroundMutex);
std::unique_lock<std::mutex> bgGuard(mBackgroundMutex);
std::queue<T>().swap(*mForegroundQueue);
std::queue<T>().swap(*mBackgroundQueue);
}
private:
// Underlying queues
std::queue<T> mQueueAlpha;
std::queue<T> mQueueBeta;
// Front and background queue references (double buffering)
std::queue<T>* mForegroundQueue;
std::queue<T>* mBackgroundQueue;
mutable std::mutex mForegroundMutex;
mutable std::mutex mBackgroundMutex;
};
} // namespace fastrtps
} // namespace eprosima
#endif // ifndef DBQUEUE_H