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/*
Copyright (C) 2007, 2008, 2009, 2010, 2011 Her Majesty the Queen in
Right of Canada (Communications Research Center Canada)
Copyright (C) 2018
Matthias P. Braendli, matthias.braendli@mpb.li
An implementation for a threadsafe queue, depends on C++11
When creating a ThreadsafeQueue, one can specify the minimal number
of elements it must contain before it is possible to take one
element out.
*/
/*
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 3 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 <https://www.gnu.org/licenses/>.
*/
#pragma once
#include <mutex>
#include <condition_variable>
#include <queue>
#include <utility>
/* This queue is meant to be used by two threads. One producer
* that pushes elements into the queue, and one consumer that
* retrieves the elements.
*
* The queue can make the consumer block until an element
* is available, or a wakeup requested.
*/
/* Class thrown by blocking pop to tell the consumer
* that there's a wakeup requested. */
class ThreadsafeQueueWakeup {};
template<typename T>
class ThreadsafeQueue
{
public:
/* Push one element into the queue, and notify another thread that
* might be waiting.
*
* if max_size > 0 and the queue already contains at least max_size elements,
* the element gets discarded.
*
* returns the new queue size.
*/
size_t push(T const& val, size_t max_size = 0)
{
std::unique_lock<std::mutex> lock(the_mutex);
size_t queue_size_before = the_queue.size();
if (max_size == 0) {
the_queue.push(val);
}
else if (queue_size_before < max_size) {
the_queue.push(val);
}
size_t queue_size = the_queue.size();
lock.unlock();
the_rx_notification.notify_one();
return queue_size;
}
size_t push(T&& val, size_t max_size = 0)
{
std::unique_lock<std::mutex> lock(the_mutex);
size_t queue_size_before = the_queue.size();
if (max_size == 0) {
the_queue.emplace(std::move(val));
}
else if (queue_size_before < max_size) {
the_queue.emplace(std::move(val));
}
size_t queue_size = the_queue.size();
lock.unlock();
the_rx_notification.notify_one();
return queue_size;
}
/* Push one element into the queue, but wait until the
* queue size goes below the threshold.
*
* Notify waiting thread.
*
* returns the new queue size.
*/
size_t push_wait_if_full(T const& val, size_t threshold)
{
std::unique_lock<std::mutex> lock(the_mutex);
while (the_queue.size() >= threshold) {
the_tx_notification.wait(lock);
}
the_queue.push(val);
size_t queue_size = the_queue.size();
lock.unlock();
the_rx_notification.notify_one();
return queue_size;
}
/* Trigger a wakeup event on a blocking consumer, which
* will receive a ThreadsafeQueueWakeup exception.
*/
void trigger_wakeup(void)
{
std::unique_lock<std::mutex> lock(the_mutex);
wakeup_requested = true;
lock.unlock();
the_rx_notification.notify_one();
}
/* Send a notification for the receiver thread */
void notify(void)
{
the_rx_notification.notify_one();
}
bool empty() const
{
std::unique_lock<std::mutex> lock(the_mutex);
return the_queue.empty();
}
size_t size() const
{
std::unique_lock<std::mutex> lock(the_mutex);
return the_queue.size();
}
bool try_pop(T& popped_value)
{
std::unique_lock<std::mutex> lock(the_mutex);
if (the_queue.empty()) {
return false;
}
popped_value = the_queue.front();
the_queue.pop();
lock.unlock();
the_tx_notification.notify_one();
return true;
}
void wait_and_pop(T& popped_value, size_t prebuffering = 1)
{
std::unique_lock<std::mutex> lock(the_mutex);
while (the_queue.size() < prebuffering and
not wakeup_requested) {
the_rx_notification.wait(lock);
}
if (wakeup_requested) {
wakeup_requested = false;
throw ThreadsafeQueueWakeup();
}
else {
std::swap(popped_value, the_queue.front());
the_queue.pop();
lock.unlock();
the_tx_notification.notify_one();
}
}
private:
std::queue<T> the_queue;
mutable std::mutex the_mutex;
std::condition_variable the_rx_notification;
std::condition_variable the_tx_notification;
bool wakeup_requested = false;
};
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