The following code example demonstrates the use of the AsyncTimeout property with the ExecuteRegisteredAsyncTasks and RegisterAsyncTask methods. Note the use of beginning, ending, and time-out handlers. In the example, an artificial delay is introduced to demonstrate the situation of an asynchronous task exceeding the allotted time for the task as specified in the AsyncTimeout property. In a real-world scenario, an asynchronous task could be used to perform database calls or image generation, for example, and the time-out handler provides graceful degradation if the task is not performed in a specified amount of time.
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<%@ Page Language="VB" AsyncTimeout="2"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
' Define the asynchronuous task.
Dim mytask As New Samples.AspNet.VB.Controls.MyAsyncTask()
Dim asynctask As New PageAsyncTask(AddressOf mytask.OnBegin, AddressOf mytask.OnEnd, AddressOf mytask.OnTimeout, DBNull.Value)
' Register the asynchronous task.
Page.RegisterAsyncTask(asynctask)
' Execute the register asynchronous task.
Page.ExecuteRegisteredAsyncTasks()
TaskMessage.InnerHtml = mytask.GetAsyncTaskProgress()
End Sub
</script>
<html >
<head runat="server">
<title>Asynchronous Task Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<span id="TaskMessage" runat="server">
</span>
</div>
</form>
</body>
</html>
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<%@ Page Language="C#" AsyncTimeout="2"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
// Define the asynchronuous task.
Samples.AspNet.CS.Controls.MyAsyncTask mytask =
new Samples.AspNet.CS.Controls.MyAsyncTask();
PageAsyncTask asynctask = new PageAsyncTask(mytask.OnBegin, mytask.OnEnd, mytask.OnTimeout, null);
// Register the asynchronous task.
Page.RegisterAsyncTask(asynctask);
// Execute the register asynchronous task.
Page.ExecuteRegisteredAsyncTasks();
TaskMessage.InnerHtml = mytask.GetAsyncTaskProgress();
}
</script>
<html >
<head runat="server">
<title>Asynchronous Task Example</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<span id="TaskMessage" runat="server">
</span>
</div>
</form>
</body>
</html>
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Imports Microsoft.VisualBasic
Imports System
Imports System.Web
Imports System.Web.UI
Imports System.Threading
Namespace Samples.AspNet.VB.Controls
Public Class MyAsyncTask
Private _taskprogress As String
Private _dlgt As AsyncTaskDelegate
' Create delegate.
Delegate Function AsyncTaskDelegate()
Public Function GetAsyncTaskProgress() As String
Return _taskprogress
End Function
Public Function DoTheAsyncTask()
' Introduce an artificial delay to simulate a delayed
' asynchronous task. Make this greater than the
' AsyncTimeout property.
Thread.Sleep(TimeSpan.FromSeconds(5.0))
End Function
' Define the method that will get called to
' start the asynchronous task.
Public Function OnBegin(ByVal sender As Object, ByVal e As EventArgs, ByVal cb As AsyncCallback, ByVal extraData As Object) As IAsyncResult
_taskprogress = "Beginning async task."
Dim _dlgt As New AsyncTaskDelegate(AddressOf DoTheAsyncTask)
Dim result As IAsyncResult = _dlgt.BeginInvoke(cb, extraData)
Return result
End Function 'OnBegin
' Define the method that will get called when
' the asynchronous task is ended.
Public Sub OnEnd(ByVal ar As IAsyncResult)
_taskprogress = "Asynchronous task completed."
_dlgt.EndInvoke(ar)
End Sub
' Define the method that will get called if the task
' is not completed within the asynchronous timeout interval.
Public Sub OnTimeout(ByVal ar As IAsyncResult)
_taskprogress = "Ansynchronous task failed to complete because " & _
"it exceeded the AsyncTimeout parameter."
End Sub
End Class
End Namespace
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using System;
using System.Web;
using System.Web.UI;
using System.Threading;
namespace Samples.AspNet.CS.Controls
{
public class MyAsyncTask
{
private String _taskprogress;
private AsyncTaskDelegate _dlgt;
// Create delegate.
protected delegate void AsyncTaskDelegate();
public String GetAsyncTaskProgress()
{
return _taskprogress;
}
public void DoTheAsyncTask()
{
// Introduce an artificial delay to simulate a delayed
// asynchronous task. Make this greater than the
// AsyncTimeout property.
Thread.Sleep(TimeSpan.FromSeconds(5.0));
}
// Define the method that will get called to
// start the asynchronous task.
public IAsyncResult OnBegin(object sender, EventArgs e,
AsyncCallback cb, object extraData)
{
_taskprogress = "Beginning async task.";
_dlgt = new AsyncTaskDelegate(DoTheAsyncTask);
IAsyncResult result = _dlgt.BeginInvoke(cb, extraData);
return result;
}
// Define the method that will get called when
// the asynchronous task is ended.
public void OnEnd(IAsyncResult ar)
{
_taskprogress = "Asynchronous task completed.";
_dlgt.EndInvoke(ar);
}
// Define the method that will get called if the task
// is not completed within the asynchronous timeout interval.
public void OnTimeout(IAsyncResult ar)
{
_taskprogress = "Ansynchronous task failed to complete " +
"because it exceeded the AsyncTimeout parameter.";
}
}
}
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