[vlc-devel] [PATCH] decoder_helpers: fix clean order

[Steve Lhomme]

On 19/02/2019 13:24, Thomas Guillem wrote:
> The module need to be unloaded before the dec struct is cleaned.
>
> This fixes an undefined behavior with threaded decoders like avcodec when they
> called decoder_UpdateVideoFormat()/dec_NewPicture() from an other thread just
> before they were unloaded.

Are there cases where the decoder is still calling 
decoder_UpdateVideoFormat() and decoder_NewPicture() while being about 
to be unloaded ? I don't see how this can work if one thread of the 
decoder is calling decoder_UpdateVideoFormat() while another thread is 
unloading the decoder DLLs. If that can happen I think the undefined 
behavior is the least of our problem.

AFAIK lavc always call decoder_UpdateVideoFormat()/decoder_NewPicture() 
from the same (decoder?) thread.

This is an important thing because the decoder pool will be released 
there as well as the video context reference count.

> ---
>   src/input/decoder_helpers.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/src/input/decoder_helpers.c b/src/input/decoder_helpers.c
> index 3cc02de8d6..b0a7c1890a 100644
> --- a/src/input/decoder_helpers.c
> +++ b/src/input/decoder_helpers.c
> @@ -48,6 +48,12 @@ void decoder_Init( decoder_t *p_dec, const es_format_t *restrict p_fmt )
>   
>   void decoder_Clean( decoder_t *p_dec )
>   {
> +    if ( p_dec->p_module != NULL )
> +    {
> +        module_unneed(p_dec, p_dec->p_module);
> +        p_dec->p_module = NULL;
> +    }
> +
>       es_format_Clean( &p_dec->fmt_in );
>       es_format_Clean( &p_dec->fmt_out );
>   
> @@ -56,11 +62,6 @@ void decoder_Clean( decoder_t *p_dec )
>           vlc_meta_Delete(p_dec->p_description);
>           p_dec->p_description = NULL;
>       }
> -    if ( p_dec->p_module != NULL )
> -    {
> -        module_unneed(p_dec, p_dec->p_module);
> -        p_dec->p_module = NULL;
> -    }
>   }
>   
>   void decoder_Destroy( decoder_t *p_dec )
> -- 
> 2.20.1
>
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