[FFmpeg-devel] [PATCH 3/3 v2] avfilter: use a mutex instead of atomics in avfilter_register()

[wm4]

On Thu,  4 Jan 2018 22:42:52 -0300
James Almer <jamrial at gmail.com> wrote:

> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavfilter/avfilter.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
> index b98b32bacb..ff7df672fd 100644
> --- a/libavfilter/avfilter.c
> +++ b/libavfilter/avfilter.c
> @@ -19,7 +19,6 @@
>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>   */
>  
> -#include "libavutil/atomic.h"
>  #include "libavutil/avassert.h"
>  #include "libavutil/avstring.h"
>  #include "libavutil/buffer.h"
> @@ -33,6 +32,7 @@
>  #include "libavutil/pixdesc.h"
>  #include "libavutil/rational.h"
>  #include "libavutil/samplefmt.h"
> +#include "libavutil/thread.h"
>  
>  #define FF_INTERNAL_FIELDS 1
>  #include "framequeue.h"
> @@ -590,19 +590,26 @@ const AVFilter *avfilter_get_by_name(const char *name)
>      return NULL;
>  }
>  
> +static AVMutex filter_register_mutex = AV_MUTEX_INITIALIZER;
> +
>  int avfilter_register(AVFilter *filter)
>  {
> -    AVFilter **f = last_filter;
> +    AVFilter **f;
>  
>      /* the filter must select generic or internal exclusively */
>      av_assert0((filter->flags & AVFILTER_FLAG_SUPPORT_TIMELINE) != AVFILTER_FLAG_SUPPORT_TIMELINE);
>  
> -    filter->next = NULL;
> +    ff_mutex_lock(&filter_register_mutex);
> +    f = last_filter;
>  
> -    while(*f || avpriv_atomic_ptr_cas((void * volatile *)f, NULL, filter))
> +    while (*f)
>          f = &(*f)->next;
> +    *f = filter;
> +    filter->next = NULL;
>      last_filter = &filter->next;
>  
> +    ff_mutex_unlock(&filter_register_mutex);
> +
>      return 0;
>  }
>  

Also seems good.