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