91 lines
3.4 KiB
C
91 lines
3.4 KiB
C
/**********************************************************************
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* $Id$
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*
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* Name: cpl_atomic_ops.h
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* Project: CPL - Common Portability Library
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* Purpose: Atomic operation functions.
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* Author: Even Rouault, <even dot rouault at spatialys.com>
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*
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**********************************************************************
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* Copyright (c) 2009-2010, Even Rouault <even dot rouault at spatialys.com>
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*
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* SPDX-License-Identifier: MIT
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****************************************************************************/
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#ifndef CPL_ATOMIC_OPS_INCLUDED
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#define CPL_ATOMIC_OPS_INCLUDED
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#include "cpl_port.h"
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CPL_C_START
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/** Add a value to a pointed integer in a thread and SMP-safe way
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* and return the resulting value of the operation.
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*
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* This function, which in most cases is implemented by a few
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* efficient machine instructions, guarantees that the value pointed
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* by ptr will be incremented in a thread and SMP-safe way.
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* The variables for this function must be aligned on a 32-bit boundary.
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*
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* Depending on the platforms, this function can also act as a
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* memory barrier, but this should not be assumed.
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*
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* Current platforms/architectures where an efficient implementation
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* exists are MacOSX, MS Windows, i386/x86_64 with GCC and platforms
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* supported by GCC 4.1 or higher. For other platforms supporting
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* the pthread library, and when GDAL is configured with thread-support,
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* the atomicity will be done with a mutex, but with
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* reduced efficiency. For the remaining platforms, a simple addition
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* with no locking will be done...
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*
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* @param ptr a pointer to an integer to increment
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* @param increment the amount to add to the pointed integer
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* @return the pointed value AFTER the result of the addition
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*/
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int CPL_DLL CPLAtomicAdd(volatile int *ptr, int increment);
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/** Increment of 1 the pointed integer in a thread and SMP-safe way
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* and return the resulting value of the operation.
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*
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* @see CPLAtomicAdd for the details and guarantees of this atomic
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* operation
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*
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* @param ptr a pointer to an integer to increment
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* @return the pointed value AFTER the operation: *ptr + 1
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*/
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#define CPLAtomicInc(ptr) CPLAtomicAdd(ptr, 1)
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/** Decrement of 1 the pointed integer in a thread and SMP-safe way
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* and return the resulting value of the operation.
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*
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* @see CPLAtomicAdd for the details and guarantees of this atomic
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* operation
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*
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* @param ptr a pointer to an integer to decrement
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* @return the pointed value AFTER the operation: *ptr - 1
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*/
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#define CPLAtomicDec(ptr) CPLAtomicAdd(ptr, -1)
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/** Compares *ptr with oldval. If *ptr == oldval, then *ptr is assigned
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* newval and TRUE is returned. Otherwise nothing is done, and FALSE is
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* returned.
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*
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* Current platforms/architectures where an efficient implementation
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* exists are MacOSX, MS Windows, i386/x86_64 with GCC and platforms
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* supported by GCC 4.1 or higher. For other platforms supporting
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* the pthread library, and when GDAL is configured with thread-support,
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* the atomicity will be done with a mutex, but with
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* reduced efficiency. For the remaining platforms, a simple compare and
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* exchange with no locking will be done...
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*
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* @param ptr a pointer to an integer (aligned on 32bit boundary).
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* @param oldval old value
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* @param newval new value
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* @return TRUE if the exchange has been done
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*/
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int CPLAtomicCompareAndExchange(volatile int *ptr, int oldval, int newval);
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CPL_C_END
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#endif /* CPL_ATOMIC_OPS_INCLUDED */
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