An object that supports the IAsyncResult interface stores state information for an asynchronous operation, and provides a synchronization object to allow threads to be signaled when the operation completes.

IAsyncResult objects are returned by methods that begin asynchronous operations, such as System.IO.FileStream.BeginRead(Byte[], int, int, AsyncCallback, object), and are passed to methods used to complete asynchronous operations, such as System.IO.FileStream.EndRead(IAsyncResult). IAsyncResult objects are also passed to methods invoked by AsyncCallback delegates when an asynchronous operation completes.