Finishes asynchronous execution of a SQL statement or stored procedure, returning the requested SADataReader.
Visual Basic Public Function EndExecuteReader( _ ByVal asyncResult As IAsyncResult _ ) As SADataReader
C# public SADataReader EndExecuteReader( IAsyncResult asyncResult );
asyncResult The IAsyncResult returned by the call to SACommand.BeginExecuteReader.
An SADataReader object that can be used to retrieve the requested rows (the same behavior as SACommand.ExecuteReader).
You must call EndExecuteReader once for every call to BeginExecuteReader. The call must be after BeginExecuteReader has returned. ADO.NET is not thread safe; it is your responsibility to ensure that BeginExecuteReader has returned. The IAsyncResult passed to EndExecuteReader must be the same as the one returned from the BeginExecuteReader call that is being completed. It is an error to call EndExecuteReader to end a call to BeginExecuteNonQuery, and vice versa.
If an error occurs while executing the command, the exception is thrown when EndExecuteReader is called.
There are four ways to wait for execution to complete:
(1) Call EndExecuteReader.
Calling EndExecuteReader blocks until the command completes. For example:
SAConnection conn = new SAConnection("DSN=SQL Anywhere 11 Demo"); conn.Open(); SACommand cmd = new SACommand( "SELECT * FROM Departments", conn ); IAsyncResult res = cmd.BeginExecuteReader(); // perform other work // this will block until the command completes SADataReader reader = cmd.EndExecuteReader( res ); |
(2) Poll the IsCompleted property of the IAsyncResult.
You can poll the IsCompleted property of the IAsyncResult. For example:
SAConnection conn = new SAConnection("DSN=SQL Anywhere 11 Demo"); conn.Open(); SACommand cmd = new SACommand( "SELECT * FROM Departments", conn ); IAsyncResult res = cmd.BeginExecuteReader(); while( !res.IsCompleted ) { // do other work } // this will not block because the command is finished SADataReader reader = cmd.EndExecuteReader( res ); |
(3) Use the IAsyncResult.AsyncWaitHandle property to get a synchronization object.
You can use the IAsyncResult.AsyncWaitHandle property to get a synchronization object, and wait on that. For example:
SAConnection conn = new SAConnection("DSN=SQL Anywhere 11 Demo"); conn.Open(); SACommand cmd = new SACommand( "SELECT * FROM Departments", conn ); IAsyncResult res = cmd.BeginExecuteReader(); // perform other work WaitHandle wh = res.AsyncWaitHandle; wh.WaitOne(); // this will not block because the command is finished SADataReader reader = cmd.EndExecuteReader( res ); |
(4) Specify a callback function when calling BeginExecuteReader
You can specify a callback function when calling BeginExecuteReader. For example:
private void callbackFunction( IAsyncResult ar ) { SACommand cmd = (SACommand) ar.AsyncState; // this won’t block since the command has completed SADataReader reader = cmd.EndExecuteReader(); } // elsewhere in the code private void DoStuff() { SAConnection conn = new SAConnection("DSN=SQL Anywhere 11 Demo"); conn.Open(); SACommand cmd = new SACommand( "SELECT * FROM Departments", conn ); IAsyncResult res = cmd.BeginExecuteReader( callbackFunction, cmd ); // perform other work. The callback function will be // called when the command completes } |
The callback function executes in a separate thread, so the usual caveats related to updating the user interface in a threaded program apply.
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