70 lines
2.3 KiB
C++
70 lines
2.3 KiB
C++
/*
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* Copyright (C) 2014 Apple Inc. All rights reserved.
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* Copyright (C) 2018 Yusuke Suzuki <utatane.tea@gmail.com>.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "Mutex.h"
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#include "ScopeExit.h"
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#if BOS(DARWIN)
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#include <mach/mach_traps.h>
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#include <mach/thread_switch.h>
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#endif
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#include <thread>
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namespace bmalloc {
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static inline void yield()
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{
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#if BOS(DARWIN)
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constexpr mach_msg_timeout_t timeoutInMS = 1;
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thread_switch(MACH_PORT_NULL, SWITCH_OPTION_DEPRESS, timeoutInMS);
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#else
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sched_yield();
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#endif
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}
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void Mutex::lockSlowCase()
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{
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// The longest critical section in bmalloc is much shorter than the
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// time it takes to make a system call to yield to the OS scheduler.
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// So, we try again a lot before we yield.
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static constexpr size_t aLot = 256;
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if (!m_isSpinning.exchange(true)) {
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auto clear = makeScopeExit([&] { m_isSpinning.store(false); });
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for (size_t i = 0; i < aLot; ++i) {
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if (try_lock())
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return;
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}
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}
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// Avoid spinning pathologically.
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while (!try_lock())
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yield();
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}
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} // namespace bmalloc
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