libcruft-util/thread/event_futex.hpp

56 lines
1.6 KiB
C++
Raw Normal View History

/*
* 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>
*/
#ifndef CRUFT_UTIL_THREAD_EVENT_HPP
#define CRUFT_UTIL_THREAD_EVENT_HPP
#include <atomic>
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
int notify_one (void);
int notify_all (void);
/// wait `count' threads that are waiting
int notify (int count);
private:
alignas (4) std::atomic<int> value;
};
}
#endif