Re: Missing GObject.connect function in typelib, but present in gir

[Andreas Rottmann <a rottmann gmx at>]

Marko Tasic <mtasic85 gmail com> writes:

> Rotty,
>
> I took look at sbank, and I think it's more advance at this point than
> pygir-ctypes.
> Good job! However, I did it this way:
>
> * created new struct that extended GClosure called PyClosure
> * added notifiers for finalize and invalidate
> * instantiated PyClosure
> * connected with "hid = GObject.signal_connect_closure(window, 'destroy',
> closure, False)"
> * runned
>
> But, it fails with "Segmentation fault" on window close.
>
> Can you explain how you did this?
>
I didn't (anywhere in the code) mess with GClosure.  Here's what I did
for signal connection (see gobject/signals.sls for the full code):

- Manually pull out the relevant function from libgobject:

  (define-c-callouts libgobject
    (connect-data% 'ulong "g_signal_connect_data"
                   '(pointer pointer fpointer pointer fpointer int))
    [...])

- Then invoke the Scheme procedure bound to that function; passing it an
  appropriate callback-wrapper (a function pointer that calls back into
  Scheme, I guess Python's ctypes does have these as well):

  (define (g-signal-connect instance signal callback)
    (define (lose msg . irritants)
      (apply error 'g-signal-connect msg irritants))
    (let*-values
        (((signal detail detailed-signal) (parse-signal-spec signal lose))
         ((prepare) (gobject-class-get-signal-callback
                     (ginstance-class instance)
                     signal)))
      (unless prepare
        (lose "no such signal" detailed-signal))
      (receive (cb-ptr reclaim) (prepare callback)
        (let* ((detailed-signal-ptr (string->utf8z-ptr detailed-signal))
               (id (connect-data%
                    (ginstance-ptr instance)
                    detailed-signal-ptr
                    cb-ptr
                    (null-pointer)
                    (callback-destroy-notify reclaim)
                   0)))
          (free detailed-signal-ptr)
          id))))

  The notable things here are:

  - I pull a callback-wrapper creation procedure using
    `gobject-class-get-signal-callback' out of the class object
    associated with the instance in question, and bind it to `prepare'.
    The class object knows about the signals and their argument/return
    types, so it can produce that callback-wrapper generator procedure.

  - Call `prepare', getting a function pointer (`cb-ptr') and a
    procedure for reclaiming the callback (`reclaim').

  - Finally, invoke g_signal_connect_data() (aka connect-data%), passing
    the function pointer and a destroy notification function pointer
    that will call `reclaim'.

HTH, Rotty
-- 
Andreas Rottmann -- <http://rotty.yi.org/>