Re: Guile GC in C++

[David Kastrup]

Jonas Hahnfeld <hahnjo@hahnjo.de> writes:

> Am Dienstag, dem 06.07.2021 um 17:03 +0200 schrieb David Kastrup:
>> Jean Abou Samra <jean@abou-samra.fr> writes:
>> 
>> >  For example, if I were the author of the below code, how 
>> >  would I understand that the mmrest_event_ should be 
>> >  unprotected? 
>> > 
>> >  void 
>> >  Part_combine_iterator::kill_mmrest (Context *c) 
>> >  { 
>> >  if (!mmrest_event_) 
>> >  { 
>> >  mmrest_event_ = new Stream_event 
>> >  (Lily::ly_make_event_class (ly_symbol2scm ("multi-measure-rest-event"))); 
>> >  set_property (mmrest_event_, "duration", SCM_EOL); 
>> >  mmrest_event_->unprotect (); 
>> >  } 
>> > 
>> >  c->event_source ()->broadcast (mmrest_event_); 
>> >  } 
>> 
>> Uh, after the call to mmrest_event_->unprotect () there is nothing that
>> would protect the newly created mmrest_event_ .
>
> Sure there is, the snippet is just too small to show the marking:
>
> void
> Part_combine_iterator::derived_mark () const
> {
>   Simultaneous_music_iterator::derived_mark ();
>
>   if (mmrest_event_)
>     scm_gc_mark (mmrest_event_->self_scm ());
> }
>
> The code makes perfect sense: If mmrest_event_ isn't set yet, the block
> will allocate and unprotect a new object so that before the broadcast,
> there is an event under the control of the iterator object for all
> possible flows through the function.

Ah, I overlooked that mmrest_event_ is not a local variable.  Sorry for
the confusion.

-- 
David Kastrup