Completion Function15

When client programs schedule asynchronous read or write operations (by calling your component's DataHScheduleData or DataHWrite functions), they furnish your component a data-handler completion function. Your component must call this function when it completes the read or write operation, whether the operation was a success or a failure.

Data handler Completion Function

The client program's completion function must present the following interface:



 
pascal void DHCompleteProc (

                     Ptr request,

                     long refcon,

                     OSErr err);

request: Specifies a pointer to the data that was associated with the read (DataHScheduleData ) or write (DataHWrite ) request. The client program uses this pointer to determine which request has completed.
refcon: Contains a reference constant that the client program supplied to your data handler component when it made the original request.
err: Indicates the success or failure of the operation. If the operation succeeded, set this parameter to 0. Otherwise, specify an appropriate error code.

DISCUSSION

Data handler completion functions are guaranteed to be called at non-interrupt time. This means that you can safely call functions that are not interrupt-safe, such as DataHScheduleData, from within a completion function.