InterlockedCompareExchangeAcquire function

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03/28/2018

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. The operation is performed with acquire memory ordering semantics.

To operate on 64-bit values, use the InterlockedCompareExchangeAcquire64 function.

Syntax

LONG __cdecl InterlockedCompareExchangeAcquire(
  _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

This 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 variables for this function must be aligned on a 32-bit boundary; otherwise, this 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_acq.

For processors that do not support acquire memory ordering semantics, this function is defined as a call to the InterlockedCompareExchange function. For more information, see WinBase.h.

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

Requirements

Minimum supported client	Windows Vista [desktop apps \| UWP apps]
Minimum supported server	Windows Server 2003 [desktop apps \| UWP apps]
Header	WinBase.h (include Windows.h)

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