[vlc-devel] [PATCH] lib: core: Use vlc_atomic_rc_t for refcounting

[Thomas Guillem]

Indeed, this instance_lock is useless now (or badly used in the dialog cbs case).

We could just add in the documentation that libvlc_dialog_set_callbacks() should be called from the same thread than libvlc_new() and before creating any media or media_player.

So, I'm OK with this patch the and the lock removal.

Nevertheless, user dialog callbacks should not be attached to the libvlc instance but to a media (when parsing) or a media_player. I know that some libvlc ports need to handle differently some dialogs depending on some contexts.

On Wed, Jun 10, 2020, at 15:32, Hugo Beauzée-Luyssen wrote:
> ---
>  lib/core.c            | 17 +++--------------
>  lib/libvlc_internal.h |  3 ++-
>  2 files changed, 5 insertions(+), 15 deletions(-)
> 
> diff --git a/lib/core.c b/lib/core.c
> index 56b985f597..8a998e3095 100644
> --- a/lib/core.c
> +++ b/lib/core.c
> @@ -60,7 +60,7 @@ libvlc_instance_t * libvlc_new( int argc, const char 
> *const *argv )
>      }
>  
>      p_new->p_libvlc_int = p_libvlc_int;
> -    p_new->ref_count = 1;
> +    vlc_atomic_rc_init( &p_new->ref_count );
>      p_new->p_callback_list = NULL;
>      vlc_mutex_init(&p_new->instance_lock);
>      return p_new;
> @@ -74,24 +74,13 @@ error:
>  void libvlc_retain( libvlc_instance_t *p_instance )
>  {
>      assert( p_instance != NULL );
> -    assert( p_instance->ref_count < UINT_MAX );
>  
> -    vlc_mutex_lock( &p_instance->instance_lock );
> -    p_instance->ref_count++;
> -    vlc_mutex_unlock( &p_instance->instance_lock );
> +    vlc_atomic_rc_inc( &p_instance->ref_count );
>  }
>  
>  void libvlc_release( libvlc_instance_t *p_instance )
>  {
> -    vlc_mutex_t *lock = &p_instance->instance_lock;
> -    int refs;
> -
> -    vlc_mutex_lock( lock );
> -    assert( p_instance->ref_count > 0 );
> -    refs = --p_instance->ref_count;
> -    vlc_mutex_unlock( lock );
> -
> -    if( refs == 0 )
> +    if(vlc_atomic_rc_dec( &p_instance->ref_count ))
>      {
>          libvlc_Quit( p_instance->p_libvlc_int );
>          libvlc_InternalCleanup( p_instance->p_libvlc_int );
> diff --git a/lib/libvlc_internal.h b/lib/libvlc_internal.h
> index 5c1107b84f..6c8ff49a81 100644
> --- a/lib/libvlc_internal.h
> +++ b/lib/libvlc_internal.h
> @@ -33,6 +33,7 @@
>  #include <vlc/libvlc_picture.h>
>  #include <vlc/libvlc_media.h>
>  #include <vlc/libvlc_events.h>
> +#include <vlc_atomic.h>
>  
>  #include <vlc_common.h>
>  
> @@ -60,7 +61,7 @@ VLC_API void libvlc_SetExitHandler( libvlc_int_t *, 
> void (*) (void *), void * );
>  struct libvlc_instance_t
>  {
>      libvlc_int_t *p_libvlc_int;
> -    unsigned      ref_count;
> +    vlc_atomic_rc_t ref_count;
>      vlc_mutex_t   instance_lock;
>      struct libvlc_callback_entry_list_t *p_callback_list;
>      struct
> -- 
> 2.20.1
> 
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