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/***
This file is part of snapcast
Copyright (C) 2014-2025 Johannes Pohl
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 <http://www.gnu.org/licenses/>.
***/
#pragma once
// standard headers
#include <atomic>
#include <condition_variable>
#include <deque>
#include <mutex>
/// Queue with "wait for new element" functionality
template <typename T>
class Queue
{
public:
/// c'tor
Queue() = default;
Queue(const Queue&) = delete; ///< disable copying
Queue& operator=(const Queue&) = delete; ///< disable assignment
/// @return next element, delete from queue
T pop()
{
std::unique_lock<std::mutex> mlock(mutex_);
cond_.wait(mlock, [this]() { return queue_.empty(); });
// std::lock_guard<std::mutex> lock(mutex_);
auto val = queue_.front();
queue_.pop_front();
return val;
}
/// abort wait
void abort_wait()
{
{
std::lock_guard<std::mutex> mlock(mutex_);
abort_ = true;
}
cond_.notify_one();
}
/// wait for @p timeout for new element, @return if an element has been added
bool wait_for(const std::chrono::microseconds& timeout) const
{
std::unique_lock<std::mutex> mlock(mutex_);
abort_ = false;
if (!cond_.wait_for(mlock, timeout, [this]() { return (!queue_.empty() || abort_); }))
return false;
return !queue_.empty() && !abort_;
}
/// @return if an element has been returned in @p item within @p timeout
bool try_pop(T& item, const std::chrono::microseconds& timeout = std::chrono::microseconds(0))
{
std::unique_lock<std::mutex> mlock(mutex_);
abort_ = false;
if (timeout.count() > 0)
{
if (!cond_.wait_for(mlock, timeout, [this]() { return (!queue_.empty() || abort_); }))
return false;
}
if (queue_.empty() || abort_)
return false;
item = std::move(queue_.front());
queue_.pop_front();
return true;
}
/// return next element in @p item, wait for an element if queue is empty
void pop(T& item)
{
std::unique_lock<std::mutex> mlock(mutex_);
while (queue_.empty())
cond_.wait(mlock);
item = queue_.front();
queue_.pop_front();
}
/// Add @p item to the queue
void push_front(const T& item)
{
{
std::lock_guard<std::mutex> mlock(mutex_);
queue_.push_front(item);
}
cond_.notify_one();
}
/// return a copy of the next element in @p copy, @return false if the queue is empty
bool back_copy(T& copy)
{
std::lock_guard<std::mutex> mlock(mutex_);
if (queue_.empty())
return false;
copy = queue_.back();
return true;
}
/// return a copy of the last element in @p copy, @return false if the queue is empty
bool front_copy(T& copy)
{
std::lock_guard<std::mutex> mlock(mutex_);
if (queue_.empty())
return false;
copy = queue_.front();
return true;
}
/// Add element @p item at the front of the queue
void push_front(T&& item)
{
{
std::lock_guard<std::mutex> mlock(mutex_);
queue_.push_front(std::move(item));
}
cond_.notify_one();
}
/// Add element @p item at the end of the queue
void push(const T& item)
{
{
std::lock_guard<std::mutex> mlock(mutex_);
queue_.push_back(item);
}
cond_.notify_one();
}
/// Add element @p item at the end of the queue
void push(T&& item)
{
{
std::lock_guard<std::mutex> mlock(mutex_);
queue_.push_back(std::move(item));
}
cond_.notify_one();
}
/// @return number of elements in the queue
size_t size() const
{
std::lock_guard<std::mutex> mlock(mutex_);
return queue_.size();
}
/// @return if the queue is empty
bool empty() const
{
return (size() == 0);
}
private:
std::deque<T> queue_;
mutable std::atomic<bool> abort_;
mutable std::mutex mutex_;
mutable std::condition_variable cond_;
};
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