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 | |
32 | namespace bmalloc { |
33 | |
34 | void 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 | |