Provides concurrency management for classes that support asynchronous method calls. This class cannot be inherited.
Assembly: System (in System.dll)
Gets or sets the synchronization context for the asynchronous operation.
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 provides a convenient way to create a class that runs properly under all application models supported by the .NET Framework.
The 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.class has one method,
For more information about implementing asynchronous classes, see Implementing the Event-based Asynchronous Pattern.
The following code example demonstrates using the AsyncOperation class, which ensures that the client's event handlers are called on the proper thread or context.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
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
Available since 10
Available since 2.0
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.