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/**********************************************************************
* $Id$
*
* Name: cpl_atomic_ops.h
* 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
****************************************************************************/
#ifndef CPL_ATOMIC_OPS_INCLUDED
#define CPL_ATOMIC_OPS_INCLUDED
#include "cpl_port.h"
CPL_C_START
/** Add a value to a pointed integer in a thread and SMP-safe way
* and return the resulting value of the operation.
*
* This function, which in most cases is implemented by a few
* efficient machine instructions, guarantees that the value pointed
* by ptr will be incremented in a thread and SMP-safe way.
* The variables for this function must be aligned on a 32-bit boundary.
*
* Depending on the platforms, this function can also act as a
* memory barrier, but this should not be assumed.
*
* Current platforms/architectures where an efficient implementation
* exists are MacOSX, MS Windows, i386/x86_64 with GCC and platforms
* supported by GCC 4.1 or higher. For other platforms supporting
* the pthread library, and when GDAL is configured with thread-support,
* the atomicity will be done with a mutex, but with
* reduced efficiency. For the remaining platforms, a simple addition
* with no locking will be done...
*
* @param ptr a pointer to an integer to increment
* @param increment the amount to add to the pointed integer
* @return the pointed value AFTER the result of the addition
*/
int CPL_DLL CPLAtomicAdd(volatile int *ptr, int increment);
/** Increment of 1 the pointed integer in a thread and SMP-safe way
* and return the resulting value of the operation.
*
* @see CPLAtomicAdd for the details and guarantees of this atomic
* operation
*
* @param ptr a pointer to an integer to increment
* @return the pointed value AFTER the operation: *ptr + 1
*/
#define CPLAtomicInc(ptr) CPLAtomicAdd(ptr, 1)
/** Decrement of 1 the pointed integer in a thread and SMP-safe way
* and return the resulting value of the operation.
*
* @see CPLAtomicAdd for the details and guarantees of this atomic
* operation
*
* @param ptr a pointer to an integer to decrement
* @return the pointed value AFTER the operation: *ptr - 1
*/
#define CPLAtomicDec(ptr) CPLAtomicAdd(ptr, -1)
/** Compares *ptr with oldval. If *ptr == oldval, then *ptr is assigned
* newval and TRUE is returned. Otherwise nothing is done, and FALSE is
* returned.
*
* Current platforms/architectures where an efficient implementation
* exists are MacOSX, MS Windows, i386/x86_64 with GCC and platforms
* supported by GCC 4.1 or higher. For other platforms supporting
* the pthread library, and when GDAL is configured with thread-support,
* the atomicity will be done with a mutex, but with
* reduced efficiency. For the remaining platforms, a simple compare and
* exchange with no locking will be done...
*
* @param ptr a pointer to an integer (aligned on 32bit boundary).
* @param oldval old value
* @param newval new value
* @return TRUE if the exchange has been done
*/
int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval);
CPL_C_END
#endif /* CPL_ATOMIC_OPS_INCLUDED */
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