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

[Thomas Guillem]

On Wed, Jan 29, 2020, at 08:49, Steve Lhomme wrote:
> On 2020-01-29 8:37, Thomas Guillem wrote:
> > Hello,
> > 
> > I would prefer to avoid using a pointer to access a mutex.
> > 
> > We will end up with modules using vlc_mutex_lock(sys->lock) and vlc_mutex_lock(&sys->lock).
> > I think it will add more confusions.
> 
> How about vlc_obj_mutex_new(vlc_object_t *, vlc_mutex_t *)

Where is the mutex stored in that case ?

The only other possibility I could see is:

vlc_obj_mutex_create(vlc_object_t *, void *objres, vlc_mutex_t *);

Example:
struct sys *sys = vlc_obj_malloc(obj, size);
vlc_obj_mutex_create(obj, sys, &sys->lock);

And vlc_obj_mutex_create() need to ensure that the mutex is stored in the objres.


> 
> The structure storage wouldn't be created (as it is now) and the mutex 
> is accessed the same way as before.
> 
> > On Tue, Jan 28, 2020, at 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
> >> 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
> >>
> >> _______________________________________________
> >> vlc-devel mailing list
> >> To unsubscribe or modify your subscription options:
> >> https://mailman.videolan.org/listinfo/vlc-devel
> > _______________________________________________
> > vlc-devel mailing list
> > To unsubscribe or modify your subscription options:
> > https://mailman.videolan.org/listinfo/vlc-devel
> > 
> _______________________________________________
> vlc-devel mailing list
> To unsubscribe or modify your subscription options:
> https://mailman.videolan.org/listinfo/vlc-devel