[vlc-devel] [RFC] [NOT FOR MERGE] objres: add mutex support

[Thomas Guillem]

On Wed, Jan 29, 2020, at 08:46, Steve Lhomme wrote:
> On 2020-01-28 21:30, Rémi Denis-Courmont wrote:
> > This adds a function to allocate a mutex that automatically gets
> > destroyed when a module fails or terminates.
> > 
> > I have very mixed feelings about this, as it introduces an error return
> > where there is normally none, i.e., from vlc_mutex_init(). It also
> > requires tedious rework to replace `vlc_mutex_t' with `vlc_mutex_t *'.
> > 
> > For reference, kernel code entirely solves this conundrum by not
> > requiring explicit mutex destruction (a kernel mutex does not hold any
> > resource besides its own `struct mutex' storage space). This could also
> > be done, but with significant reworking of the VLC threading layer and
> 
> Dunno about other OSes, but on Windows our mutex uses a critical section 
> that needs to be released.

That's not the question, vlc will always require vlc_mutex_destroy because there will be always some OSses that need it.
Btw, posix need it too.

> 
> > prevents reliable detection of attempt to delete a still-in-use mutex.
> > ---
> >   include/vlc_objects.h |  2 ++
> >   src/misc/objres.c     | 15 +++++++++++++++
> >   2 files changed, 17 insertions(+)
> > 
> > diff --git a/include/vlc_objects.h b/include/vlc_objects.h
> > index 19ee5207fc..32f23abf41 100644
> > --- a/include/vlc_objects.h
> > +++ b/include/vlc_objects.h
> > @@ -295,5 +295,7 @@ VLC_API VLC_MALLOC char *vlc_obj_strdup(vlc_object_t *obj, const char *str);
> >    */
> >   VLC_API void vlc_obj_free(vlc_object_t *obj, void *ptr);
> >   
> > +VLC_API VLC_MALLOC vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj);
> > +
> >   /** @} */
> >   /** @} */
> > diff --git a/src/misc/objres.c b/src/misc/objres.c
> > index cac8624e7e..383dd760a8 100644
> > --- a/src/misc/objres.c
> > +++ b/src/misc/objres.c
> > @@ -174,3 +174,18 @@ void vlc_obj_free(vlc_object_t *obj, void *ptr)
> >   {
> >       vlc_objres_remove(obj, ptr, ptrcmp);
> >   }
> > +
> > +static void mutex_release(void *data)
> > +{
> > +    vlc_mutex_destroy(data);
> > +}
> > +
> > +vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj)
> > +{
> > +    vlc_mutex_t *mtx = vlc_objres_new(sizeof (*mtx), mutex_release);
> > +    if (mtx != NULL) {
> > +        vlc_mutex_init(mtx);
> > +        vlc_objres_push(obj, mtx);
> > +    }
> > +    return mtx;
> > +}
> > -- 
> > 2.25.0
> > 
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> > 
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