This documentation is archived and is not being maintained.

ThreadPool.UnsafeQueueUserWorkItem Method

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)

static member UnsafeQueueUserWorkItem : 
        callBack:WaitCallback * 
        state:Object -> bool 


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 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.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • SecurityCriticalAttribute 

    Requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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