1 /*
2 * Copyright (C) 2013 Google 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 are
6 * met:
7 *
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * * Redistributions in binary form must reproduce the above
11 * copyright notice, this list of conditions and the following disclaimer
12 * in the documentation and/or other materials provided with the
13 * distribution.
14 * * Neither the name of Google Inc. nor the names of its
15 * contributors may be used to endorse or promote products derived from
16 * this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31 #ifndef WTF_SpinLock_h
32 #define WTF_SpinLock_h
33
34 // DESCRIPTION
35 // spinLockLock() and spinLockUnlock() are simple spinlock primitives based on
36 // the standard CPU primitive of atomic increment and decrement of an int at
37 // a given memory address.
38
39 #include "wtf/Atomics.h"
40
41 namespace WTF {
42
spinLockLock(int volatile * lock)43 ALWAYS_INLINE void spinLockLock(int volatile* lock)
44 {
45 while (UNLIKELY(atomicTestAndSetToOne(lock))) {
46 while (*lock) { } // Spin without spamming locked instructions.
47 }
48 }
49
spinLockUnlock(int volatile * lock)50 ALWAYS_INLINE void spinLockUnlock(int volatile* lock)
51 {
52 atomicSetOneToZero(lock);
53 }
54
55 } // namespace WTF
56
57 using WTF::spinLockLock;
58 using WTF::spinLockUnlock;
59
60 #endif // WTF_SpinLock_h
61