Page 180 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes
Member Description
AsyncState An optional application-specific object that contains
information regarding the asynchronous operation.
AsyncWaitHandle A WaitHandle that can be used to block application
implementation until the asynchronous operation
completes.
CompletedSynchronously A value that indicates whether the asynchronous operation
completed on the thread used to call BeginOperation
Name instead of completing on a separate ThreadPoolthread.

IsCompleted A value that signifies whether the asynchronous operation
has finished.

A Begin Operation Name method takes any parameters stated in the signature of the synchronous
edition of the method that are passed by value or by reference. Any out parameters are not part
of the Begin Operation Namemethod signature. The BeginOperationName method signature
also involves two additional parameters. The first of these defines an AsyncCallback delegate
that references a technique that is called when the asynchronous operation finishes. The caller
can specify null (Nothing in Visual Basic) if it does not want a technique invoked when the
operation completes. The second additional parameter is a user-defined object. This object can
be used to pass application-specific state information to the technique raised when the
asynchronous operation completes. If a BeginOperationName method takes additional operation-
specific parameters, like a byte array to amass bytes read from a file, the AsyncCallback and
application state object are the last parameters in the BeginOperation Namemethod signature.

Begin OperationName returns control to the calling thread instantly. If the BeginOperationName
technique throws exceptions, the exceptions are thrown previous to the asynchronous operation
is started.

Did u know? If the BeginOperationNamemethod throws exceptions, the callback method
is not invoked.

11.2.2 Ending an Asynchronous Operation

The End Operation Name technique ends asynchronous operation OperationName. The return
value of the EndOperationName method is the same type returned by its synchronous
counterpart and is particular to the asynchronous operation.

Example: The EndRead method returns the number of bytes read from a FileStream and
the EndGetHostByName method returns an IPHostEntry object that includes information
regarding a host computer.

The EndOperationName method takes any out or ref parameters stated in the signature of the
synchronous edition of the method. In addition to the parameters from the synchronous method,
the EndOperationName method also contains an IAsyncResult parameter.

!
Caution Callers must pass the instance returned by the analogous call to
BeginOperationName.

174 LOVELY PROFESSIONAL UNIVERSITY