Asynchronous Delegates
Sometimes it is desirable to call a method asynchronously, so the call returns immediately while the method executes on a separate thread. The runtime provides a standard way that any method can be called asynchronously, taking into account retrieving return values and ref/in parameters supplied to the method. When the C# compiler encounters a delegate, the delegate derived class it generates contains three key methods:
return-type Invoke (parameter-list); IAsyncResult BeginInvoke (parameter-list, AsyncCallback ac, object state); return-type EndInvoke (ref/out-only parameter-list, IAsyncCallback ac);
Calling Invoke( )
calls the method synchronously,
and the caller has to wait until the delegate finishes executing (a
standard delegate invocation in C# calls Invoke( )
).
Calling BeginInvoke( )
invokes the delegate with
the supplied parameter list, then immediately returns. This
asynchronous call is performed as soon as a thread is available in
the ThreadPool. Two additional parameters are added to
BeginInvoke( )
: an
AsyncCallback
object, to optionally specify a
delegate to execute by the ThreadPool thread just before it returns,
and an arbitrary object to hold state. The
AsyncCallback
delegate signature is a void method
with a single IAsyncResult
parameter, which lets
you access information about the call.
Calling EndInvoke( )
retrieves the return value of
the called method, along with any ref/out parameters that may have
been modified.
In the following example, ...
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