third_party/WebKit/Source/wtf/SpinLock.h

   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,
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  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
  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
  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