Defines a pointer to a completion function. Your completion function is executed by the File Manager after the completion of a File Manager function call.

typedef void(* IOCompletionProcPtr) (
    ParmBlkPtr paramBlock
);

You would declare your function like this if you were to name it MyIOCompletionCallback:

void MyIOCompletionCallback (
    ParmBlkPtr paramBlock
);

paramBlock

DISCUSSION

When you execute a File Manager function asynchronously (an Async function), you can specify a completion routine by passing the routine’s address in the ioCompletion field of the parameter block passed to the function. Because you requested asynchronous execution, the File Manager places an I/O request in the file I/O queue and returns control to your application—possibly even before the actual I/O operation is completed. The File Manager takes requests from the queue one at a time and processes them; meanwhile, your application is free to do other processing.

A function executed asynchronously returns control to your application with the result code noErr as soon as the call is placed in the file I/O queue. This result code does not indicate that the call has successfully completed, but simply indicates that the call was successfully placed in the queue. To determine when the call is actually completed, you can inspect the ioResult field of the parameter block. This field is set to a positive number when the call is made and set to the actual result code when the call is completed. If you specify a completion routine, it is executed after the result code is placed in ioResult.

SPECIAL CONSIDERATIONS

Because a completion routine is executed at interrupt time, it should not allocate, move, or purge memory (either directly or indirectly) and should not depend on the validity of handles to unlocked blocks.

If your completion routine uses application global variables, it must also ensure that register A5 contains the address of the boundary between your application global variables and your application parameters.

AVAILABILITY

Supported in Carbon.

© 2000 Apple Computer, Inc. — (Last Updated 5/8/2000)