Source/WTF/wtf/Atomics.cpp

/*
 * Copyright (C) 2007, 2008, 2010, 2012 Apple Inc. All rights reserved.
 * Copyright (C) 2007 Justin Haygood (jhaygood@reaktix.com)
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer. 
 * 2.  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. 
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") 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 APPLE AND ITS 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 APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * Note: The implementations of InterlockedIncrement and InterlockedDecrement are based
 * on atomic_increment and atomic_exchange_and_add from the Boost C++ Library. The license
 * is virtually identical to the Apple license above but is included here for completeness.
 *
 * Boost Software License - Version 1.0 - August 17th, 2003
 * 
 * Permission is hereby granted, free of charge, to any person or organization
 * obtaining a copy of the software and accompanying documentation covered by
 * this license (the "Software") to use, reproduce, display, distribute,
 * execute, and transmit the Software, and to prepare derivative works of the
 * Software, and to permit third-parties to whom the Software is furnished to
 * do so, all subject to the following:
 * 
 * The copyright notices in the Software and this entire statement, including
 * the above license grant, this restriction and the following disclaimer,
 * must be included in all copies of the Software, in whole or in part, and
 * all derivative works of the Software, unless such copies or derivative
 * works are solely in the form of machine-executable object code generated by
 * a source language processor.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
 * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
 * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include "config.h"
#include "Atomics.h"

// Some architectures, like MIPS32, don't have GCC implementation for builtin __sync_* functions
// with 64 bits variable size. Official GCC answer for the problem: If a target doesn't support
// atomic operations on certain variable sizes, you are out of luck with atomicity in that case
// (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56296). GCC >= 4.8 will support __atomic_* builtin
// functions for this purpose for all the GCC targets, but for current compilers we have to include
// our own implementation.
#if COMPILER(GCC) && !defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8) && USE(LOCKFREE_THREADSAFEREFCOUNTED) && USE(PTHREADS)

#include "ThreadingPrimitives.h"

namespace WTF {

static const size_t kSwapLockCount = 32;
static Mutex s_swapLocks[kSwapLockCount];

static inline Mutex& getSwapLock(const volatile int64_t* addr)
{
    return s_swapLocks[(reinterpret_cast<intptr_t>(addr) >> 3U) % kSwapLockCount];
}

static int64_t atomicStep(int64_t volatile* addend, int64_t step)
{
    Mutex& mutex = getSwapLock(addend);

    mutex.lock();
    int64_t value = *addend + step;
    *addend = value;
    mutex.unlock();

    return value;
}

extern "C" {

int64_t __sync_add_and_fetch_8(int64_t volatile* addend, int64_t value)
{
    return atomicStep(addend, value);
}

int64_t __sync_sub_and_fetch_8(int64_t volatile* addend, int64_t value)
{
    return atomicStep(addend, -value);
}

} // extern "C"

} // namespace WTF

#endif