54 lines
1.5 KiB
C++
54 lines
1.5 KiB
C++
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/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_THREAD_EVENT_HPP
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#define CRUFT_UTIL_THREAD_EVENT_HPP
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#include <atomic>
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namespace cruft::thread {
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/// a reusable synchronisation object that allows threads to wait until
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/// notify is called.
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///
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/// there is no internal state so it is easy to create races between wait
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/// and notify calls. this makes the class mostly suitable for recurring
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/// events.
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///
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/// the user should ensure no callers are waiting at destruction time
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/// otherwise they may remain blocked indefinitely.
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///
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/// the address of the object is important so it must _never_ be
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/// relocated in any manner if any caller may be waiting. it may be safe
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/// to do so if there are no callers waiting (but the relevant functions
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/// are deleted for safety anyway).
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class event {
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public:
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event ();
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event (const event&) = delete;
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event (event&&) = delete;
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event& operator= (const event&) = delete;
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event& operator= (event&&) = delete;
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/// block until notified
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void wait (void);
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/// wake all threads that are waiting
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int notify (void);
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/// wait `count' threads that are waiting
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int notify (int count);
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private:
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alignas (4) std::atomic<int> value;
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};
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}
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#endif
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