ThreadPool.QueueUserWorkItem Method (WaitCallback)

You can place data required by the queued method in the instance fields of the class in which the method is defined, or you can use the QueueUserWorkItem(WaitCallback, Object) overload that accepts an object containing the necessary data.

Note
Visual Basic users can omit the WaitCallback constructor, and simply use the AddressOf operator when passing the callback method to QueueUserWorkItem. Visual Basic automatically calls the correct delegate constructor.

Version Information

The following example uses the QueueUserWorkItem(WaitCallback) method overload to queue a task, which is represented by the ThreadProc method, to execute when a thread becomes available. No task information is supplied with this overload. Therefore, the information that is available to the ThreadProc method is limited to the object the method belongs to.

using System;
using System.Threading;
public class Example {
    public static void Main() {
        // Queue the task.
        ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc));

        Console.WriteLine("Main thread does some work, then sleeps.");
        // If you comment out the Sleep, the main thread exits before 
        // the thread pool task runs.  The thread pool uses background 
        // threads, which do not keep the application running.  (This 
        // is a simple example of a race condition.)
        Thread.Sleep(1000);

        Console.WriteLine("Main thread exits.");
    }

    // This thread procedure performs the task. 
    static void ThreadProc(Object stateInfo) {
        // No state object was passed to QueueUserWorkItem, so  
        // stateInfo is null.
        Console.WriteLine("Hello from the thread pool.");
    }
}

.NET Framework

.NET Framework Client Profile

Portable Class Library

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Reference

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