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ThreadPool.UnsafeQueueUserWorkItem Method

Updated: December 2009

Queues the specified delegate to the thread pool, but does not propagate the calling stack to the worker thread.

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

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.NoFlags|SecurityPermissionFlag.ControlEvidence|SecurityPermissionFlag.ControlPolicy)]
public static bool UnsafeQueueUserWorkItem(
	WaitCallback callBack,
	Object state


Type: System.Threading.WaitCallback

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

Type: System.Object

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

Return Value

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


The caller does not have the required permission.


An out-of-memory condition was encountered.


The work item could not be queued.


callBack is null.

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 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0




December 2009

Corrected the description.

Customer feedback.