Name
IAsyncResult
Synopsis
This interface is used in asynchronous
programming to act as a placeholder for the result of the async call. It
is most commonly used when an instance of a delegate type is fired
using the BeginInvoke method. (This idiom is used
extensively throughout the .NET Framework Class Library.)
Asynchronous method calls can be harvested in a number of ways.
A programmer can poll the call by checking the IsCompleted
property of the IAsyncResult object to see if the call
has completed yet. This, while perhaps the simplest approach, is also likely
the most wasteful, as the caller needs to be in some sort of
spin loop, repeatedly checking the property until a true is received.
A variant of the polling spin loop is to use the AsyncWaitHandle
property of IAsyncResult. This is a standard Win32
handle that can be used in some of the synchronization primitives provided
in the System.Threading namespace. Specifically, this
property is a System.Threading.WaitHandle instance, meaning
that the programmer can call any of the Wait methods: WaitOne(),
WaitAny(), or
WaitAll(). The net
effect
is the same — put the calling thread to sleep until the async call
completes.
Although not formally part of the IAsyncResult interface,
a corresponding EndInvoke
method is supported by delegates. The EndInvoke method blocks the calling thread until the async call completes. Alternatively, at the point of the async delegate call, a programmer can specify a callback delegate to call when the ...