Interlocked.CompareExchange Method (Object, Object, Object)

Compares two objects for reference equality and, if they are equal, replaces one of the objects.

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

public static Object CompareExchange (
	ref Object location1,
	Object value,
	Object comparand
public static Object CompareExchange (
	/** @ref */ Object location1, 
	Object value, 
	Object comparand
JScript does not support passing value-type arguments by reference.



The destination object that is compared with comparand and possibly replaced.


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


The object that is compared to the object at location1.

Return Value

The original value in location1.

Exception typeCondition


The address of location1 is a null pointer.

If comparand and the object 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.

Beginning with .NET Framework version 2.0, the CompareExchange(J,J,J) method overload provides a type-safe alternative for reference types.


The objects are compared for reference equality, rather than Object.Equals. As a result, two boxed instances of the same value type (for example, the integer 3) always appear to be unequal, and no operation is performed. Do not use this overload with value types.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0