For those of you not wanting to actually test and validate a chatbot to see the results, I've done it for you with
@jmacz's example using Copilot so you can come to your own conclusions:
Me: compliant with "Inside Macintosh", how would you add custom vars to a parameter block during asynchronous calls?
Copilot Response
To add custom variables to a parameter block during asynchronous calls in a way that is compliant with
Inside Macintosh, you'd typically use the
ioRefNum or
ioCompletion fields in the parameter block to store or reference your custom data. Here's how this was commonly done in classic Mac OS programming:
Background: Parameter Blocks and Asynchronous Calls
In the classic Mac OS, many system calls (especially I/O-related ones) used
parameter blocks (like ParamBlockRec, IOParam, DrvQEl, etc.) to pass information. For asynchronous calls, the system would call back via the ioCompletion function pointer when the operation completed.
Compliant Way to Add Custom Vars
To safely add custom data:
1. Use a Custom Completion Routine
You can define your own ioCompletion routine that wraps the original one and includes a pointer to your custom data.
2. Embed Custom Data in a Wrapper Structure
Create a structure that includes the parameter block and your custom variables:
typedef struct {
ParamBlockRec pb;
void *myCustomData;
IOCompletionUPP originalCompletion;
} MyPBWrapper;
3. Set ioCompletion to Your Wrapper Function
In your wrapper function, you can access the custom data, then call the original completion routine if needed.
void MyCompletionRoutine(ParmBlkPtr pb) {
MyPBWrapper *wrapper = (MyPBWrapper *)pb;
// Access your custom data
void *data = wrapper->myCustomData;
// Do something with the data...
// Call the original completion routine if it exists
if (wrapper->originalCompletion) {
wrapper->originalCompletion((ParmBlkPtr)&wrapper->pb);
}
// Free the wrapper if dynamically allocated
DisposePtr((Ptr)wrapper);
}
4. Initiate the Async Call
When making the async call:
MyPBWrapper *wrapper = (MyPBWrapper *)NewPtrClear(sizeof(MyPBWrapper));
wrapper->myCustomData = ...; // your custom data
wrapper->originalCompletion = myOriginalCompletion;
wrapper->pb.ioCompletion = NewIOCompletionUPP(MyCompletionRoutine);
// Set up other fields in wrapper->pb...
PBReadAsync((ParmBlkPtr)&wrapper->pb);
Important Notes
- Always ensure memory is properly managed—especially if allocating wrappers dynamically.
- This approach is compliant with Inside Macintosh because it respects the structure and behavior of the parameter block and ioCompletion mechanism.
- Avoid modifying undocumented or reserved fields in the parameter block.
Would you like a concrete example using PBReadAsync or PBControlAsync?
Note that it'll be just as confident no matter whether it is correct or not. Usually it's correct, but if it gets something wrong, you'll have to either catch it yourself, or challenge the bot on it a few times. If it doesn't get something usable after 3 tries, best not to keep trying and just ask it a different question, like which page you should look up the information on.
