1/*
2 * Copyright (C) 2014 Apple Inc. All rights reserved.
3 * Copyright (C) 2018 Yusuke Suzuki <utatane.tea@gmail.com>.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
15 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
17 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
18 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
19 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
20 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
21 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
22 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
24 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include "Mutex.h"
28
29#include "ScopeExit.h"
30#include <thread>
31
32namespace bmalloc {
33
34void Mutex::lockSlowCase()
35{
36 // The longest critical section in bmalloc is much shorter than the
37 // time it takes to make a system call to yield to the OS scheduler.
38 // So, we try again a lot before we yield.
39 static const size_t aLot = 256;
40
41 if (!m_isSpinning.exchange(true)) {
42 auto clear = makeScopeExit([&] { m_isSpinning.store(false); });
43
44 for (size_t i = 0; i < aLot; ++i) {
45 if (try_lock())
46 return;
47 }
48 }
49
50 // Avoid spinning pathologically.
51 while (!try_lock())
52 sched_yield();
53}
54
55} // namespace bmalloc
56