62 lines
1.9 KiB
C++
62 lines
1.9 KiB
C++
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/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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_JOB_EVENT_HPP
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#define CRUFT_UTIL_JOB_EVENT_HPP
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#include <atomic>
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namespace util::job {
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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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