1/*
2 * Copyright (C) 2013 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 ByteSpinLock_h
27#define ByteSpinLock_h
28
29#include <thread>
30#include <wtf/Assertions.h>
31#include <wtf/Atomics.h>
32#include <wtf/Locker.h>
33#include <wtf/Noncopyable.h>
34
35namespace WTF {
36
37class ByteSpinLock {
38    WTF_MAKE_NONCOPYABLE(ByteSpinLock);
39public:
40    ByteSpinLock()
41        : m_lock(0)
42    {
43    }
44
45    void lock()
46    {
47        while (!weakCompareAndSwap(&m_lock, 0, 1))
48            std::this_thread::yield();
49        memoryBarrierAfterLock();
50    }
51
52    void unlock()
53    {
54        memoryBarrierBeforeUnlock();
55        m_lock = 0;
56    }
57
58    bool isHeld() const { return !!m_lock; }
59
60private:
61    uint8_t m_lock;
62};
63
64typedef Locker<ByteSpinLock> ByteSpinLocker;
65
66} // namespace WTF
67
68using WTF::ByteSpinLock;
69using WTF::ByteSpinLocker;
70
71#endif // ByteSpinLock_h
72