Tcl Extension Architecture (TEA) Sample Extension

The sample extension has no Sample_Unload procedure and thus, may not be unloaded.

It was made clear that the sample extension only shows the minimum. This would add complexity.

Message by Ashok on the core list on this:

Am 12.12.2024 um 09:11 schrieb [email protected]:
The unload command is fraught with too many perils imho to get right in the general case and also of limited value.

I would not clutter the sample extension with either of these but of course your opinion may differ.

/Ashok

Branch and ticket closed. Thank you all, Harald

Emiliano has pointed to interpreter Assoc data.

So, here is the proposed change: [eba8935a06].

I copy some of the information given by Emiliano here:

You get (at least!) three "levels" for storing cliendata to Tcl:

• Per command, using the clientdata argument of Tcl_CreateObjCommand().
• Per interp, using Tcl_{Set|Get}AssocData().
• Per thread, using Tcl_GetThreadData().

In this case, Tcl_GetAssocData is to be used, since you want to wipe the command out from the current interpreter, leaving other interps alone. A simple example (untested !!!)

#define MY_PKG_KEY "My great package key"
Tcl_InterpDeleteProc pkgInterpDeleted; /* called when the interp is deleted */
struct CmdClientData {
    Tcl_Command sha1CmdToken;
};

Sample_Init:
    struct CmdClientData *cmdClientDataPtr;
    cmdClientDataPtr = ckalloc(sizeof(struct CmdClientData));
    Tcl_SetAssocData(interp, MY_PKG_KEY, pkgInterpDeleted, cmdClientDataPtr); 
    cmdClientDataPtr->sha1CmdToken = Tcl_CreateObjCommand(
        interp, "sha1", (Tcl_ObjCmdProc *)Sha1_Cmd,
        cmdClientDataPtr, Sha1_CmdDeleteProc);

Sample_Unload:
    struct CmdClientData *cmdClientDataPtr = (struct CmdClientData *)
        Tcl_GetAssocData(interp, MY_PKG_KEY, NULL);
    /* check whether the pointer is not NULL */
    Tcl_DeleteCommandFromToken(interp, cmdClientDataPtr->sha1CmdToken);
    ckfree(cmdClientDataPtr);
    Tcl_DeleteAssocData(interp, MY_PKG_KEY);

Of course you have to juggle the interaction of Sample_Unload, Sha1CmdDeleteProc and pkgInterpDeleted, since they can be called when:

• [sha1] cmd is deleted (Sha1_CmdDeleteProc is called).
• interp is destroyed (pkgInterpDeleted is called).
• [unload] is called on the external library (Sample_Unload is called).

Ok, checkin [2c5e0e025e] adds thread safety for the sha1 command.

And the command tolkens are also saved in a struct.

But how to get the command tolken struct ot the unload procedure ?

Thanks for any hint, Harald

To late, I am already totally discourraged.
It is sooooo complicated...

Thanks, I may look into this back in a year when I understand at least 5%...

The token must be stored in "clientdata". Something, I never understood....

Thanks,
Harald

Well, I don't want to discourage you, but ... what if someone does a "rename sha1 somethingelse"? Then the Tcl_DeleteCommand() wont work. Solution: remember the token when the command was created, and remove that.

Yes, for multi interpreter/threads, see ticket [ecf13be4c9].

I tried to remove the commands by commit [37a2611f73].

Thanks for the information.

Learning each day...

Harald

This won't be sufficient. All memory occupied by the extensions should be released, so the "sha1" and the "::sample::build-info" commands must be removed from the interpreter. Otherwise, those commands can still be called, which leads to a crash (and not only because sha1Contexts and ctxtotalRead are NULL).

B.T.W.: sha1Contexts and ctxtotalRead being global static variables is a bad idea too...... Accessing the "sha1" command from multiple interpreters (or - worse - from multiple threads) will give surprises!

Proposal in commit [d1f80795ac] within branch [19630c0c-unload]