Source/wtf/SpinLock.h

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 */

#ifndef WTF_SpinLock_h
#define WTF_SpinLock_h

// DESCRIPTION
// spinLockLock() and spinLockUnlock() are simple spinlock primitives based on
// the standard CPU primitive of atomic increment and decrement of an int at
// a given memory address.

#include "wtf/Atomics.h"

namespace WTF {

ALWAYS_INLINE void spinLockLock(int volatile* lock)
{
    while (UNLIKELY(atomicTestAndSetToOne(lock))) {
        while (*lock) { } // Spin without spamming locked instructions.
    }
}

ALWAYS_INLINE void spinLockUnlock(int volatile* lock)
{
    atomicSetOneToZero(lock);
}

} // namespace WTF

using WTF::spinLockLock;
using WTF::spinLockUnlock;

#endif // WTF_SpinLock_h