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

[Thomas Guillem]

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.

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
> 
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