Interlocked.CompareExchange Method (Double%, Double, Double)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Compares two double-precision floating point numbers for equality and, if they are equal, replaces one of the values.
Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)
Syntax
Public Shared Function CompareExchange ( _
ByRef location1 As Double, _
value As Double, _
comparand As Double _
) As Double
public static double CompareExchange(
ref double location1,
double value,
double comparand
)
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.
Exceptions
| Exception | Condition |
|---|---|
| NullReferenceException | The address of location1 is a null pointer. |
Remarks
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.
Examples
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.
Version Information
Windows Phone OS
Supported in: 8.1, 8.0