[FFmpeg-devel] [PATCH 2/3 v2] avformat: use mutexes instead of atomics in av_register_{input, output}_format()

[wm4]

On Thu,  4 Jan 2018 22:41:38 -0300
James Almer <jamrial at gmail.com> wrote:

> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavformat/format.c | 34 +++++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/libavformat/format.c b/libavformat/format.c
> index 38ca2a3465..759b5b1ab4 100644
> --- a/libavformat/format.c
> +++ b/libavformat/format.c
> @@ -19,10 +19,10 @@
>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>   */
>  
> -#include "libavutil/atomic.h"
>  #include "libavutil/avstring.h"
>  #include "libavutil/bprint.h"
>  #include "libavutil/opt.h"
> +#include "libavutil/thread.h"
>  
>  #include "avio_internal.h"
>  #include "avformat.h"
> @@ -58,28 +58,40 @@ AVOutputFormat *av_oformat_next(const AVOutputFormat *f)
>          return first_oformat;
>  }
>  
> +static AVMutex iformat_register_mutex = AV_MUTEX_INITIALIZER;
> +
>  void av_register_input_format(AVInputFormat *format)
>  {
> -    AVInputFormat **p = last_iformat;
> +    AVInputFormat **p;
> +
> +    ff_mutex_lock(&iformat_register_mutex);
> +    p = last_iformat;
>  
> -    // Note, format could be added after the first 2 checks but that implies that *p is no longer NULL
> -    while(p != &format->next && !format->next && avpriv_atomic_ptr_cas((void * volatile *)p, NULL, format))
> +    while (*p)
>          p = &(*p)->next;
> +    *p = format;
> +    format->next = NULL;
> +    last_iformat = &format->next;
>  
> -    if (!format->next)
> -        last_iformat = &format->next;
> +    ff_mutex_unlock(&iformat_register_mutex);
>  }
>  
> +static AVMutex oformat_register_mutex = AV_MUTEX_INITIALIZER;
> +
>  void av_register_output_format(AVOutputFormat *format)
>  {
> -    AVOutputFormat **p = last_oformat;
> +    AVOutputFormat **p;
> +
> +    ff_mutex_lock(&oformat_register_mutex);
> +    p = last_oformat;
>  
> -    // Note, format could be added after the first 2 checks but that implies that *p is no longer NULL
> -    while(p != &format->next && !format->next && avpriv_atomic_ptr_cas((void * volatile *)p, NULL, format))
> +    while (*p)
>          p = &(*p)->next;
> +    *p = format;
> +    format->next = NULL;
> +    last_oformat = &format->next;
>  
> -    if (!format->next)
> -        last_oformat = &format->next;
> +    ff_mutex_unlock(&oformat_register_mutex);
>  }
>  
>  int av_match_ext(const char *filename, const char *extensions)

Can't see anything wrong with it.