Interlocked.CompareExchange Method (Double, Double, Double)

 

Compares two double-precision floating point numbers for equality and, if they are equal, replaces the first value.

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

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

Parameters

location1
Type: System.Double

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

value
Type: System.Double

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

comparand
Type: System.Double

The value that is compared to the value at location1.

Return Value

Type: System.Double

The original value in location1.

Exception Condition
NullReferenceException

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 of Double values. Two threads add a series of Double values using the thread-safe method and ordinary addition, and when the threads complete the totals are compared. On a dual-processor computer, there is a significant difference in the totals.

In the thread-safe method, 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.

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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