Programming .NET Components, 2nd Edition

Asynchronous Call Programming Models

To support asynchronous invocation, multiple threads are required. However, it would be a waste of system resources and a performance penalty if .NET spun off a new thread for every asynchronous method invocation. A better approach is to use a pool of already created worker threads. .NET has just such a pool, called the .NET thread pool . One of the nice things about the .NET way of supporting asynchronous calls is that it hides this interaction completely. As previously indicated, there are quite a few programming models available for dealing with asynchronous calls. This section examines the various options: blocking, waiting, polling, and completion callbacks. In general, BeginInvoke() initiates an asynchronous method invocation. The calling client is blocked for only the briefest moment—the time it takes to queue up a request for a thread from the thread pool to execute the method—and then control returns to the client. EndInvoke() manages method completion; specifically, retrieving output parameters and return values, and error handling.

Using BeginInvoke() and EndInvoke()

The compiler-generated BeginInvoke() and EndInvoke() methods take this form:

    public virtual IAsyncResult BeginInvoke(<input and input/output parameters>,
                                            AsyncCallback callback,
                                            object asyncState);
    public virtual <return value> EndInvoke(<output and input/output parameters>,
                                            IAsyncResult asyncResult);

BeginInvoke() accepts the input parameters of the original signature the ...