Interlocked.CompareExchange Method (Int32, Int32, Int32)


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Compares two 32-bit signed integers for equality and, if they are equal, replaces the first value.

Namespace:   System.Threading
Assembly:  mscorlib (in mscorlib.dll)

static member CompareExchange : 
        location1:int byref *
        value:int *
        comparand:int -> int


Type: System.Int32

The destination, whose value is compared with comparand and possibly replaced.

Type: System.Int32

The value that replaces the destination value if the comparison results in equality.

Type: System.Int32

The value that is compared to the value at location1.

Return Value

Type: System.Int32

The original value in location1.

Exception Condition

The address of location1 is a null pointer.

If comparand and the value in location1 are equal, then value is stored in location1. Otherwise, no operation is performed. The compare and exchange operations are performed as an atomic operation. The return value of CompareExchange is the original value in location1, whether or not the exchange takes place.

The following code example demonstrates a thread-safe method that accumulates a running total. The initial value of the running total is saved, and then the CompareExchange method is used to exchange the newly computed total with the old total. If the return value is not equal to the saved value of the running total, then another thread has updated the total in the meantime. In that case, the attempt to update the running total must be repeated.


The Add method, introduced in version 2.0 of the .NET Framework, provides a more convenient way to accumulate thread-safe running totals for integers.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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