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ThreadPool.UnsafeQueueUserWorkItem Method

Registers a delegate to wait for a WaitHandle.

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

public static bool UnsafeQueueUserWorkItem (
	WaitCallback callBack,
	Object state
public static boolean UnsafeQueueUserWorkItem (
	WaitCallback callBack, 
	Object state
public static function UnsafeQueueUserWorkItem (
	callBack : WaitCallback, 
	state : Object
) : boolean
Not applicable.



A WaitCallback that represents the delegate to invoke when a thread in the thread pool picks up the work item.


The object that is passed to the delegate when serviced from the thread pool.

Return Value

true if the method succeeds; OutOfMemoryException is thrown if the work item could not be queued.

Exception typeCondition


The caller does not have the required permission.


An out-of-memory condition was encountered.


The work item could not be queued.


callBack is a null reference (Nothing in Visual Basic).

Unlike the QueueUserWorkItem method, UnsafeQueueUserWorkItem does not propagate the calling stack to the worker thread. This allows code to lose the calling stack and thereby to elevate its security privileges.

Caution noteCaution:

Using UnsafeQueueUserWorkItem could inadvertently open up a security hole. Code access security bases its permission checks on the permissions of all the callers on the stack. When work is queued on a thread pool thread using UnsafeQueueUserWorkItem, the stack of the thread pool thread will not have the context of the actual callers. Malicious code might be able exploit this to avoid permission checks.

Windows 98, Windows Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0