WaitHandle Class
Assembly: mscorlib (in mscorlib.dll)
'Declaration <ComVisibleAttribute(True)> _ Public MustInherit Class WaitHandle Inherits MarshalByRefObject Implements IDisposable 'Usage Dim instance As WaitHandle
/** @attribute ComVisibleAttribute(true) */ public abstract class WaitHandle extends MarshalByRefObject implements IDisposable
ComVisibleAttribute(true) public abstract class WaitHandle extends MarshalByRefObject implements IDisposable
This class is typically used as a base class for synchronization objects. Classes derived from WaitHandle define a signaling mechanism to indicate taking or releasing access to a shared resource, but use the inherited WaitHandle methods to block while waiting for access to shared resources.
Use the static methods of this class to block a thread until one or more synchronization objects receive a signal.
The following code example shows how two threads can do background tasks while the Main thread waits for the tasks to complete using the static WaitAny and WaitAll methods of the WaitHandle class.
Imports System Imports System.Threading NotInheritable Public Class App ' Define an array with two AutoResetEvent WaitHandles. Private Shared waitHandles() As WaitHandle = _ {New AutoResetEvent(False), New AutoResetEvent(False)} ' Define a random number generator for testing. Private Shared r As New Random() <MTAThreadAttribute> _ Public Shared Sub Main() ' Queue two tasks on two different threads; ' wait until all tasks are completed. Dim dt As DateTime = DateTime.Now Console.WriteLine("Main thread is waiting for BOTH tasks to complete.") ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(0)) ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(1)) WaitHandle.WaitAll(waitHandles) ' The time shown below should match the longest task. Console.WriteLine("Both tasks are completed (time waited={0})", _ (DateTime.Now - dt).TotalMilliseconds) ' Queue up two tasks on two different threads; ' wait until any tasks are completed. dt = DateTime.Now Console.WriteLine() Console.WriteLine("The main thread is waiting for either task to complete.") ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(0)) ThreadPool.QueueUserWorkItem(AddressOf DoTask, waitHandles(1)) Dim index As Integer = WaitHandle.WaitAny(waitHandles) ' The time shown below should match the shortest task. Console.WriteLine("Task {0} finished first (time waited={1}).", _ index + 1,(DateTime.Now - dt).TotalMilliseconds) End Sub 'Main Shared Sub DoTask(ByVal state As [Object]) Dim are As AutoResetEvent = CType(state, AutoResetEvent) Dim time As Integer = 1000 * r.Next(2, 10) Console.WriteLine("Performing a task for {0} milliseconds.", time) Thread.Sleep(time) are.Set() End Sub 'DoTask End Class 'App ' This code produces output similar to the following: ' ' Main thread is waiting for BOTH tasks to complete. ' Performing a task for 7000 milliseconds. ' Performing a task for 4000 milliseconds. ' Both tasks are completed (time waited=7064.8052) ' ' The main thread is waiting for either task to complete. ' Performing a task for 2000 milliseconds. ' Performing a task for 2000 milliseconds. ' Task 1 finished first (time waited=2000.6528).
System.MarshalByRefObject
System.Threading.WaitHandle
System.Threading.EventWaitHandle
System.Threading.Mutex
System.Threading.Semaphore
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, 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.