Note:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: SharedState. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

If your class needs to provide asynchronous behavior according to the Event-based Asynchronous Pattern Overview, you will encounter a number of concurrency management issues. Among these is the requirement to ensure that event handlers are called on a thread or context that is appropriate for the application model (for example, Windows Forms applications, ASP.NET applications, console applications, and so on). The AsyncOperationManager provides a convenient way to create a class that runs properly under all application models supported by the .NET Framework.

The AsyncOperationManager class has one method, CreateOperation, which returns an System.ComponentModel..::.AsyncOperation that can be used to track the duration of a particular asynchronous task. The System.ComponentModel..::.AsyncOperation for a task can be used to alert clients when a task completes. It can also be used to post progress updates and incremental results without terminating the operation.

For more information about implementing asynchronous classes, see Implementing the Event-based Asynchronous Pattern.

The following code example demonstrates using the AsyncOperationManager class to create a class that supports asynchronous operations for any application model. It shows how to implement a class that tests a number to determine whether it is prime. This calculation can be time consuming, so it is done on a separate thread. Progress reports, incremental results, and completion notifications are handled by the AsyncOperation class, which ensures that the client's event handlers are called on the proper thread or context.

For a full code listing, see How to: Implement a Component That Supports the Event-based Asynchronous Pattern. For a full code listing of a client form, see How to: Implement a Client of the Event-based Asynchronous Pattern.

' This method starts an asynchronous calculation. 
' First, it checks the supplied task ID for uniqueness.
' If taskId is unique, it creates a new WorkerEventHandler 
' and calls its BeginInvoke method to start the calculation.
Public Overridable Sub CalculatePrimeAsync( _
    ByVal numberToTest As Integer, _
    ByVal taskId As Object)

    ' Create an AsyncOperation for taskId.
    Dim asyncOp As AsyncOperation = _
        AsyncOperationManager.CreateOperation(taskId)

    ' Multiple threads will access the task dictionary,
    ' so it must be locked to serialize access.
    SyncLock userStateToLifetime.SyncRoot
        If userStateToLifetime.Contains(taskId) Then
            Throw New ArgumentException( _
                "Task ID parameter must be unique", _
                "taskId")
        End If

        userStateToLifetime(taskId) = asyncOp
    End SyncLock

    ' Start the asynchronous operation.
    Dim workerDelegate As New WorkerEventHandler( _
        AddressOf CalculateWorker)

    workerDelegate.BeginInvoke( _
        numberToTest, _
        asyncOp, _
        Nothing, _
        Nothing)

End Sub

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

.NET Framework

Reference

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