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103 lines
2.5 KiB
C++
103 lines
2.5 KiB
C++
/*
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* yamc_backoff_spin.hpp
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*
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* MIT License
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*
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* Copyright (c) 2017 yohhoy
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#ifndef YAMC_BACKOFF_SPIN_HPP_
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#define YAMC_BACKOFF_SPIN_HPP_
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#include <thread>
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/// default backoff spin policy
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#ifndef YAMC_BACKOFF_SPIN_DEFAULT
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#define YAMC_BACKOFF_SPIN_DEFAULT yamc::backoff::exponential<>
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#endif
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/// initial count for yamc::backoff::exponential<>
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#ifndef YAMC_BACKOFF_EXPONENTIAL_INITCOUNT
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#define YAMC_BACKOFF_EXPONENTIAL_INITCOUNT 4000
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#endif
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namespace yamc {
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/*
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* backoff algorithm for spinlock basic_mutex<BackoffPolicy>
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*
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* - yamc::backoff::exponential<InitCount>
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* - yamc::backoff::yield
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* - yamc::backoff::busy
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*/
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namespace backoff {
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/// exponential backoff spin policy
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template <
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unsigned int InitCount = YAMC_BACKOFF_EXPONENTIAL_INITCOUNT
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>
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struct exponential {
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struct state {
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unsigned int initcount = InitCount;
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unsigned int counter = InitCount;
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};
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static void wait(state& s)
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{
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if (s.counter == 0) {
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// yield thread at exponential decreasing interval
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std::this_thread::yield();
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s.initcount = (s.initcount >> 1) | 1;
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s.counter = s.initcount;
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}
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--s.counter;
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}
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};
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/// simple yield thread policy
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struct yield {
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struct state {};
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static void wait(state&)
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{
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std::this_thread::yield();
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}
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};
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/// 'real' busy-loop policy
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///
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/// ATTENTION:
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/// This policy may waste your CPU time.
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///
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struct busy {
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struct state {};
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static void wait(state&) {}
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};
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} // namespace backoff
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} // namespace yamc
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#endif
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