InterlockedCompareExchangePointer function

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

To operate on non-pointer values, use the InterlockedCompareExchange function.

Syntax

C++


PVOID __cdecl InterlockedCompareExchangePointer(
  _Inout_ PVOID volatile *Destination,
  _In_    PVOID          Exchange,
  _In_    PVOID          Comparand
);

Parameters

Destination [in, out]: A pointer to 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.

On a 64-bit system, the parameters are 64 bits and must be aligned on 64-bit boundaries; otherwise, the function will behave unpredictably. On a 32-bit system, the parameters are 32 bits and must be aligned on 32-bit boundaries.

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 _InterlockedCompareExchangePointer.

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 InterlockedCompareExchangePointerAcquire or InterlockedCompareExchangePointerRelease 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)