WaitHandle.WaitOne Method (Int32)

Parameters

• millisecondsTimeout
  Type: System.Int32
  The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.

Return Value

Type: System.Boolean
true if the current instance receives a signal; otherwise, false.

Imports System.Threading

' The following imports simplify the supporting code; they are not required for 
' WaitHandle:
Imports System.Windows.Controls
Imports System.Windows.Input

Public Class Example

   Private Shared outputBlock As System.Windows.Controls.TextBlock
   Private Shared autoEvent As New AutoResetEvent(False)
   Private Shared threadCount As Integer = 0

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Example.outputBlock = outputBlock

      For i As Integer = 1 To 3
         Interlocked.Increment(threadCount)
         ThreadPool.QueueUserWorkItem(AddressOf WorkMethod, i)
      Next i

      AddHandler outputBlock.MouseLeftButtonUp, AddressOf MouseUp

   End Sub

   Private Shared Sub WorkMethod(ByVal stateInfo As Object)

      Dim number As Integer = CInt(stateInfo)
      outputBlock.Dispatcher.BeginInvoke(displayHelper, _
                 String.Format("Task {0} is queued. Click to release." & vbLf, number))

      Dim start As DateTime = DateTime.Now
      While Not autoEvent.WaitOne(3000)
         outputBlock.Dispatcher.BeginInvoke(displayHelper, _
            String.Format("Task {0} has waited {1} seconds. Click to release." & vbLf, _
                          number, _
                          (DateTime.Now - start).TotalMilliseconds))
      End While

      outputBlock.Dispatcher.BeginInvoke(displayHelper, _
                 String.Format("Task {0} is ending." & vbLf, number))

      If Interlocked.Decrement(threadCount) = 0 Then

         ' Disable the mouse.
         outputBlock.Dispatcher.BeginInvoke(unhookHelper)

         outputBlock.Dispatcher.BeginInvoke(displayHelper, _
                              "Refresh the page to run the demo again." & vbLf)

      End If
   End Sub

   Private Shared Sub MouseUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs)

      ' Release a thread.
      autoEvent.Set()

   End Sub

   ' Helper methods:

   ' In order to update the TextBlock object, which is on the UI thread, you must
   ' make a cross-thread call by using the Dispatcher object that is associated 
   ' with the TextBlock. The DisplayOutput helper method and its delegate, 
   ' displayHelper, are used by the BeginInvoke method of the Dispatcher object
   ' to append text to the TextBlock. UnhookMouseUp and its delegate, unhookHelper,
   ' unhook the event handler for the MouseLeftButtonUp event.
   '
   Private Shared displayHelper As New Action(Of String)(AddressOf DisplayOutput)
   Private Shared Sub DisplayOutput(ByVal msg As String)
      outputBlock.Text &= msg 
   End Sub

   Private Shared unhookHelper As New Action(AddressOf UnhookMouseUp)
   Private Shared Sub UnhookMouseUp()
      RemoveHandler outputBlock.MouseLeftButtonUp, AddressOf MouseUp
   End Sub

End Class

' This example produces output similar to the following:
'
'Task 1 is queued. Click to release.
'Task 2 is queued. Click to release.
'Task 3 is queued. Click to release.
'Task 2 has waited 3010.7421 seconds. Click to release.
'Task 1 has waited 3026.3418 seconds. Click to release.
'Task 3 has waited 3010.7421 seconds. Click to release.
'Task 3 is ending.
'Task 1 has waited 6037.0839 seconds. Click to release.
'Task 2 has waited 6021.4842 seconds. Click to release.
'Task 2 is ending.
'Task 1 is ending.
'Refresh the page to run the demo again.

using System;
using System.Threading;

// The following imports simplify the supporting code; they are not required for 
// WaitHandle:
using System.Windows.Controls;
using System.Windows.Input;

public class Example
{
   private static System.Windows.Controls.TextBlock outputBlock;
   private static AutoResetEvent autoEvent = new AutoResetEvent(false);
   private static int threadCount = 0;

   public static void Demo(TextBlock outputBlock)
   {
      Example.outputBlock = outputBlock;

      for(int i = 1; i <= 3; i++)
      {
         Interlocked.Increment(ref threadCount);
         ThreadPool.QueueUserWorkItem(WorkMethod, i);
      }

      outputBlock.MouseLeftButtonUp += MouseUp;
   }

   private static void WorkMethod(object stateInfo)
   {
      int number = (int) stateInfo;
      outputBlock.Dispatcher.BeginInvoke(displayHelper, 
            String.Format("Task {0} is queued. Click to release.\n", number));

      DateTime start = DateTime.Now;
      while (!autoEvent.WaitOne(3000))
      {
         outputBlock.Dispatcher.BeginInvoke(displayHelper, 
            String.Format("Task {0} has waited {1} seconds. Click to release.\n", 
                          number, 
                          (DateTime.Now-start).TotalMilliseconds));
      }

      outputBlock.Dispatcher.BeginInvoke(displayHelper, 
                     String.Format("Task {0} is ending.\n", number));

      if (Interlocked.Decrement(ref threadCount) == 0)
      {
         // Disable the mouse.
         outputBlock.Dispatcher.BeginInvoke(delegate () {
                                   outputBlock.MouseLeftButtonUp -= MouseUp; });

         outputBlock.Dispatcher.BeginInvoke(displayHelper, 
                         "Refresh the page to run the demo again.\n");               
      }
   }

   private static void MouseUp(object sender, MouseButtonEventArgs e)
   {
      // Release a thread.
      autoEvent.Set();
   }

   // Helper methods:

   // In order to update the TextBlock object, which is on the UI thread, you must
   // make a cross-thread call by using the Dispatcher object that is associated 
   // with the TextBlock. The DisplayOutput helper method and its delegate, 
   // displayHelper, are used by the BeginInvoke method of the Dispatcher object
   // to append text to the TextBlock. 
   //
   private static Action<string> displayHelper = new Action<string>(DisplayOutput);
   private static void DisplayOutput(string msg)
   {
      outputBlock.Text += msg;
   }
}

/* This example produces output similar to the following:

Task 1 is queued. Click to release.
Task 2 is queued. Click to release.
Task 3 is queued. Click to release.
Task 2 has waited 3010.7421 seconds. Click to release.
Task 1 has waited 3026.3418 seconds. Click to release.
Task 3 has waited 3010.7421 seconds. Click to release.
Task 3 is ending.
Task 1 has waited 6037.0839 seconds. Click to release.
Task 2 has waited 6021.4842 seconds. Click to release.
Task 2 is ending.
Task 1 is ending.
Refresh the page to run the demo again.
 */