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Inside Macintosh: Interapplication Communication /

Chapter 12 - Data Access Manager / Using the Data Access Manager

Executing Routines Asynchronously

All of the Data Access Manager low-level routines and some of the high-level routines can execute asynchronously--that is, the routine returns control to your application before the routine has completed execution. Your application must call the Event Manager's WaitNextEvent function periodically to allow an asynchronous routine to complete execution.

Note

The database extension is responsible for implementing asynchronous execution of Data Access Manager routines. For example, if you call the DBSend function to send a query to a data server, and the database extension calls a device driver, the database extension can return control to your application as soon as the device driver has placed its routine in the driver input/output (I/O) queue. If you attempt to execute a routine asynchronously and the database extension that the user has selected does not support asynchronous execution, the routine returns a result code of rcDBAsyncNotSupp and terminates execution.

All Data Access Manager routines that can execute asynchronously take as a parameter a pointer to a parameter block known as the asynchronous parameter block. If the value of this pointer is NIL, the function is executed synchronously--that is, the routine does not return control to your application until execution is complete.