InterlockedCompareExchange function (HLSL reference)
Atomically compares the destination with the comparison value. If they are identical, the destination is overwritten with the input value. The original value is set to the destination's original value.
Syntax
void InterlockedCompareExchange(
in R dest,
in T compare_value,
in T value,
out T original_value
);
Parameters

dest [in]

Type: R
The destination address.

compare_value [in]

Type: T
The comparison value.

value [in]

Type: T
The input value.

original_value [out]

Type: T
The original value.
Return value
This function does not return a value.
Remarks
Atomically compares the value referenced by dest with compare_value, stores value in the location referenced by dest if the values match, returns the original value of dest in original_value. This operation can only be performed on int or uint typed resources and shared memory variables. There are two possible uses for this function. The first is when R is a shared memory variable type. In this case, the function performs the operation on the shared memory register referenced by dest. The second scenario is when R is a resource variable type. In this scenario, the function performs the operation on the resource location referenced by dest. This operation is only available when R is readable and writable.
Note
If you call InterlockedCompareExchange in a for or while compute shader loop, to properly compile, you must use the [allow_uav_condition] attribute on that loop.
Minimum Shader Model
This function is supported in the following shader models.
Shader Model  Supported 

Shader Model 5 and higher shader models  yes 
This function is supported in the following types of shaders:
Vertex  Hull  Domain  Geometry  Pixel  Compute 

x  x  x  x  x  x 
See also