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InterlockedCompareExchange routine

The InterlockedCompareExchange routine performs an atomic operation that compares the input value pointed to by Destination with the value of Comparand.

Syntax


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

Parameters

Destination [in, out]

A pointer to the input value that is compared with the value of Comparand.

Exchange [in]

Specifies the output value pointed to by Destination if the input value pointed to by Destination equals the value of Comparand.

Comparand [in]

Specifies the value that is compared with the input value pointed to by Destination.

Return value

InterlockedCompareExchange returns the original value of *Destination.

Remarks

If Comparand is equal to *Destination, then *Destination is set to equal Exchange. Otherwise, *Destination is unchanged.

InterlockedCompareExchange provides a fast, atomic way to synchronize the testing and updating of a variable that is shared by multiple threads. If the input value pointed to by Destination equals the value of Comparand, the output value of Destination is set to the value of Exchange.

InterlockedCompareExchange is designed for speed and, typically, is implemented inline by a compiler. InterlockedCompareExchange is atomic only with respect to other InterlockedXxx calls. It does not use a spin lock and can be safely used on pageable data.

Interlocked operations cannot be used on non-cached memory.

Requirements

Version

Available starting with Windows 2000.

Header

Wdm.h (include Wdm.h, Ntddk.h, or Ntifs.h)

IRQL

Any level

See also

ExInterlockedCompareExchange64
InterlockedCompareExchangePointer
InterlockedDecrement
InterlockedExchange
InterlockedExchangePointer
InterlockedIncrement

 

 

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