[gobo-eiffel-develop] Callback from C to Eiffel

[Berend de B. <be...@po...>]

Hi Eric,

Can I callback from C to Eiffel? Need this at a few places in eposix,
for example to support signals.

For example this the code used for ISE:

  EIF_TYPE_ID tid;
  EIF_OBJECT temp;
  if ( signal_switch !=3D NULL ) {
    temp =3D signal_switch;
    signal_switch =3D NULL;
    eif_unfreeze (frozen_signal_switch);
    frozen_signal_switch =3D NULL;
    eif_wean (temp);
  }
  if ( a_switch !=3D NULL ) {
    tid =3D eif_type_id ("STDC_SIGNAL_SWITCH");
    signal_callback =3D eif_procedure ("switcher", tid);
    if (signal_callback =3D=3D 0)
      { eif_panic ("switcher feature not found."); }
    frozen_signal_switch =3D eif_freeze (a_switch);
    signal_switch =3D eif_adopt (a_switch);
  }

I.e. the callback pointer is "calculated" at set time and stored in
signal_switch. When a signal occurs, this call is made:

  (signal_callback) (frozen_signal_switch, sig);


SmartEiffel has a different strategy. When a feature is exported, SE
simply generates a prototype for it in the cecil.h file:

  /* Available Eiffel routines via -cecil:
  */
  void stdc_exit_switch_at_exit(void* C);
  void stdc_signal_switch_switcher(void* C,T2 a1);

And within C I can simply call stdc_signal_switch_switcher to make the
callback to Eiffel.

=2D-=20
Cheers,

Berend de Boer