1/*
2 * Copyright (C) 2014 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#ifndef StaticMutex_h
27#define StaticMutex_h
28
29#include "BAssert.h"
30#include <atomic>
31
32// A fast replacement for std::mutex for use in static storage, where global
33// constructors and exit-time destructors are prohibited.
34
35namespace bmalloc {
36
37class StaticMutex {
38public:
39    void lock();
40    bool try_lock();
41    void unlock();
42
43private:
44    friend class Mutex;
45
46    // Static storage will zero-initialize us automatically, but Mutex needs an
47    // API for explicit initialization.
48    void init();
49
50    void lockSlowCase();
51
52    std::atomic_flag m_flag;
53};
54
55inline void StaticMutex::init()
56{
57    m_flag.clear();
58}
59
60inline bool StaticMutex::try_lock()
61{
62    return !m_flag.test_and_set(std::memory_order_acquire);
63}
64
65inline void StaticMutex::lock()
66{
67    if (!try_lock())
68        lockSlowCase();
69}
70
71inline void StaticMutex::unlock()
72{
73    m_flag.clear(std::memory_order_release);
74}
75
76} // namespace bmalloc
77
78#endif // StaticMutex_h
79