libcruft-util/thread/event_std.hpp

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/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Copyright 2018 Danny Robson <danny@nerdcruft.net>
*/
#pragma once
#include <atomic>
#include <mutex>
#include <condition_variable>
namespace cruft::thread {
/// a reusable synchronisation object that allows threads to wait until
/// notify is called.
///
/// there is no internal state so it is easy to create races between wait
/// and notify calls. this makes the class mostly suitable for recurring
/// events.
///
/// the user should ensure no callers are waiting at destruction time
/// otherwise they may remain blocked indefinitely.
///
/// the address of the object is important so it must _never_ be
/// relocated in any manner if any caller may be waiting. it may be safe
/// to do so if there are no callers waiting (but the relevant functions
/// are deleted for safety anyway).
class event {
public:
event ();
event (const event&) = delete;
event (event&&) = delete;
event& operator= (const event&) = delete;
event& operator= (event&&) = delete;
/// block until notified
void wait (void);
/// wake all threads that are waiting
void notify_one (void);
/// wait `count' threads that are waiting
void notify_all (void);
private:
std::atomic<int> m_value;
std::mutex m_mutex;
std::condition_variable m_cv;
};
}