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InterlockedCompareExchange function

Performs an atomic compare-and-exchange operation on the specified values. The function compares two specified 32-bit values and exchanges with another 32-bit value based on the outcome of the comparison.

If you are exchanging pointer values, this function has been superseded by the InterlockedCompareExchangePointer function.

To operate on 64-bit values, use the InterlockedCompareExchange64 function.

Syntax


LONG __cdecl InterlockedCompareExchange(
  _Inout_  LONG volatile *Destination,
  _In_     LONG Exchange,
  _In_     LONG Comparand
);

Parameters

Destination [in, out]

A pointer to the destination value.

Exchange [in]

The exchange value.

Comparand [in]

The value to compare to Destination.

Return value

The function returns the initial value of the Destination parameter.

Remarks

The function compares the Destination value with the Comparand value. If the Destination value is equal to the Comparand value, the Exchange value is stored in the address specified by Destination. Otherwise, no operation is performed.

The parameters for this function must be aligned on a 32-bit boundary; otherwise, the function will behave unpredictably on multiprocessor x86 systems and any non-x86 systems. See _aligned_malloc.

The interlocked functions provide a simple mechanism for synchronizing access to a variable that is shared by multiple threads. This function is atomic with respect to calls to other interlocked functions.

This function is implemented using a compiler intrinsic where possible. For more information, see the WinBase.h header file and _InterlockedCompareExchange.

This function generates a full memory barrier (or fence) to ensure that memory operations are completed in order.

Itanium-based systems:  For performance-critical applications, use InterlockedCompareExchangeAcquire or InterlockedCompareExchangeRelease instead.

Note  This function is supported on Windows RT-based systems.

Note  

Requirements

Minimum supported client

Windows XP [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2003 [desktop apps | Windows Store apps]

Header

WinBase.h (include Windows.h)

Library

Kernel32.lib

DLL

Kernel32.dll

See also

Interlocked Variable Access
InterlockedCompare64Exchange128
InterlockedCompareExchangeAcquire
InterlockedCompareExchangeRelease
InterlockedCompareExchangeNoFence
InterlockedCompareExchange16
InterlockedCompareExchange16Acquire
InterlockedCompareExchange16Release
InterlockedCompareExchange16NoFence
InterlockedCompareExchange64
InterlockedCompareExchangeAcquire64
InterlockedCompareExchangeRelease64
InterlockedCompareExchangeNoFence64
InterlockedCompareExchange128
InterlockedCompareExchangePointer
InterlockedCompareExchangePointerAcquire
InterlockedCompareExchangePointerRelease
InterlockedCompareExchangePointerNoFence
Synchronization Functions

 

 

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