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/**************************************************************************
*
* Copyright (C) 2017 Intel Corporation.
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*
**************************************************************************/
#pragma once
#include <array>
#include <atomic>
#include <thread>
template<typename T, unsigned M>
class message_queue {
public:
message_queue() : head(), tail() {}
///
/// Push item into the message queue. Will block until the queue
/// contains less than M elements.
///
void
push(T &&x) {
const unsigned idx = head.load(std::memory_order_relaxed);
while ((idx + 1) % M == tail.load(std::memory_order_acquire))
std::this_thread::yield();
q[head] = std::move(x);
head.store((idx + 1) % M, std::memory_order_release);
}
///
/// Pop item from the message queue. Will block if the queue is
/// empty.
///
T
pop() {
const unsigned idx = tail.load(std::memory_order_relaxed);
while (head.load(std::memory_order_acquire) == idx)
std::this_thread::yield();
T x = std::move(q[idx]);
tail.store((idx + 1) % M, std::memory_order_release);
return std::move(x);
}
///
/// Pop item from the message queue. Will return
/// value-initialized item if the queue is empty.
///
T
try_pop() {
const unsigned idx = tail.load(std::memory_order_relaxed);
if (head.load(std::memory_order_acquire) == idx) {
return {};
} else {
T x = std::move(q[idx]);
tail.store((idx + 1) % M, std::memory_order_release);
return std::move(x);
}
}
private:
std::atomic<unsigned> head;
std::atomic<unsigned> tail;
std::array<T, M> q;
};
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