cpl_atomic_ops.cpp

/**********************************************************************
 *
 * Name:     cpl_atomic_ops.cpp
 * Project:  CPL - Common Portability Library
 * Purpose:  Atomic operation functions.
 * Author:   Even Rouault, <even dot rouault at spatialys.com>
 *
 **********************************************************************
 * Copyright (c) 2009-2010, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "cpl_atomic_ops.h"

#include "cpl_config.h"

// TODO: If C++11, use #include <atomic>.

#if defined(_MSC_VER)

#include <windows.h>

int CPLAtomicAdd(volatile int *ptr, int increment)
{
    return InterlockedExchangeAdd((volatile LONG *)(ptr), (LONG)(increment)) +
           increment;
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    return (LONG)InterlockedCompareExchange((volatile LONG *)(ptr),
                                            (LONG)newval,
                                            (LONG)oldval) == (LONG)oldval;
}

#elif defined(__MINGW32__) && defined(__i386__)

#include <windows.h>

int CPLAtomicAdd(volatile int *ptr, int increment)
{
    return InterlockedExchangeAdd((LONG *)(ptr), (LONG)(increment)) + increment;
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    return (LONG)InterlockedCompareExchange((LONG *)(ptr), (LONG)newval,
                                            (LONG)oldval) == (LONG)oldval;
}

#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))

int CPLAtomicAdd(volatile int *ptr, int increment)
{
    int temp = increment;
    __asm__ __volatile__("lock; xaddl %0,%1"
                         : "+r"(temp), "+m"(*ptr)
                         :
                         : "memory");
    return temp + increment;
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    unsigned char ret;

    __asm__ __volatile__(" lock; cmpxchgl %2,%1\n"
                         " sete %0\n"
                         : "=q"(ret), "=m"(*ptr)
                         : "r"(newval), "m"(*ptr), "a"(oldval)
                         : "memory");

    return static_cast<int>(ret);
}

#elif defined(HAVE_GCC_ATOMIC_BUILTINS)
// Starting with GCC 4.1.0, built-in functions for atomic memory access are
// provided.  See:
//   http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html
// We use a ./configure test to determine whether this builtins are available.
// as it appears that the GCC 4.1 version used on debian etch is broken when
// linking such instructions.
int CPLAtomicAdd(volatile int *ptr, int increment)
{
    if (increment > 0)
        return __sync_add_and_fetch(ptr, increment);

    return __sync_sub_and_fetch(ptr, -increment);
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    return __sync_bool_compare_and_swap(ptr, oldval, newval);
}

#elif defined(__MACH__) && defined(__APPLE__)

#include <libkern/OSAtomic.h>

int CPLAtomicAdd(volatile int *ptr, int increment)
{
    return OSAtomicAdd32(increment, (int *)(ptr));
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    return OSAtomicCompareAndSwap32(oldval, newval, (int *)(ptr));
}

#elif !defined(CPL_MULTIPROC_PTHREAD)
#warning "Needs real lock API to implement properly atomic increment"

// Dummy implementation.
int CPLAtomicAdd(volatile int *ptr, int increment)
{
    (*ptr) += increment;
    return *ptr;
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    if (*ptr == oldval)
    {
        *ptr = newval;
        return TRUE;
    }
    return FALSE;
}

#else

#include "cpl_multiproc.h"

static CPLLock *hAtomicOpLock = nullptr;

// Slow, but safe, implementation using a mutex.
int CPLAtomicAdd(volatile int *ptr, int increment)
{
    CPLLockHolderD(&hAtomicOpLock, LOCK_SPIN);
    (*ptr) += increment;
    return *ptr;
}

int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval)
{
    CPLLockHolderD(&hAtomicOpLock, LOCK_SPIN);
    if (*ptr == oldval)
    {
        *ptr = newval;
        return TRUE;
    }
    return FALSE;
}

#endif