[FFmpeg-devel] [PATCH 1/3 v2] avcodec/util: use a mutex instead of atomics in avcodec_register()

[wm4]

On Thu,  4 Jan 2018 22:40:44 -0300
James Almer <jamrial at gmail.com> wrote:

> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavcodec/utils.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index dfbfe98d63..4d736d2e7d 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -26,7 +26,6 @@
>   */
>  
>  #include "config.h"
> -#include "libavutil/atomic.h"
>  #include "libavutil/attributes.h"
>  #include "libavutil/avassert.h"
>  #include "libavutil/avstring.h"
> @@ -127,17 +126,24 @@ int av_codec_is_decoder(const AVCodec *codec)
>      return codec && (codec->decode || codec->receive_frame);
>  }
>  
> +static AVMutex codec_register_mutex = AV_MUTEX_INITIALIZER;
> +
>  av_cold void avcodec_register(AVCodec *codec)
>  {
>      AVCodec **p;
>      avcodec_init();
> +
> +    ff_mutex_lock(&codec_register_mutex);
>      p = last_avcodec;
> -    codec->next = NULL;
>  
> -    while(*p || avpriv_atomic_ptr_cas((void * volatile *)p, NULL, codec))
> +    while (*p)
>          p = &(*p)->next;
> +    *p          = codec;
> +    codec->next = NULL;
>      last_avcodec = &codec->next;
>  
> +    ff_mutex_unlock(&codec_register_mutex);
> +
>      if (codec->init_static_data)
>          codec->init_static_data(codec);
>  }

Seems good, but should init_static_data really be outside of the lock?
(Sure, it wasn't under a look before either, but still.)