[vlc-devel] [PATCH 3/4] sout: lock sout_stream_t individually

[Steve Lhomme]

This lock looks like in belongs in the duplicate module rather that do a 
lock for all sout_stream_t users.

On 2020-10-11 16:30, Rémi Denis-Courmont wrote:
> The stream output is called from multiple threads without
> synchronisation, notably at least one thread per ES decoder. Normally,
> the stream output instance (sout_instance_t) lock will serialise all
> calls to the first stream output module instance (sout_stream_t) in the
> stream output chain.
> 
> This is not practical if there is also concurrency within the chain.
> One notable case is when the select/duplicate module is used in filter
> mode and one of the select/duplicate target is threaded, e.g.:
> 
>   #duplicate{dst=transcode{...},dst=transcode{...}}:std{...}
> 
> In that example, the standard output can be called from both transcode
> filters.
> 
> To solve this, add a lock for each element in the stream output chain.
> Alternatively, we could drop filter mode from select/duplicate, leaving
> only the (more common) output mode where duplicate is the last element
> in the chain.
> ---
>   src/stream_output/stream_output.c | 44 +++++++++++++++++++++++++++----
>   1 file changed, 39 insertions(+), 5 deletions(-)
> 
> diff --git a/src/stream_output/stream_output.c b/src/stream_output/stream_output.c
> index e0769dc749..069fe57346 100644
> --- a/src/stream_output/stream_output.c
> +++ b/src/stream_output/stream_output.c
> @@ -736,38 +736,71 @@ static void mrl_Clean( mrl_t *p_mrl )
>   
>   struct sout_stream_private {
>       sout_stream_t stream;
> +    vlc_mutex_t lock;
>       module_t *module;
>   };
>   
>   #define sout_stream_priv(s) \
>           container_of(s, struct sout_stream_private, stream)
>   
> +static void sout_StreamLock(sout_stream_t *s)
> +{
> +    vlc_mutex_lock(&sout_stream_priv(s)->lock);
> +}
> +
> +static void sout_StreamUnlock(sout_stream_t *s)
> +{
> +    vlc_mutex_unlock(&sout_stream_priv(s)->lock);
> +}
> +
>   void *sout_StreamIdAdd(sout_stream_t *s, const es_format_t *fmt)
>   {
> -    return s->ops->add(s, fmt);
> +    void *id;
> +
> +    sout_StreamLock(s);
> +    id = s->ops->add(s, fmt);
> +    sout_StreamUnlock(s);
> +    return id;
>   }
>   
>   void sout_StreamIdDel(sout_stream_t *s, void *id)
>   {
> +    sout_StreamLock(s);
>       s->ops->del(s, id);
> +    sout_StreamUnlock(s);
>   }
>   
>   int sout_StreamIdSend(sout_stream_t *s, void *id, block_t *b)
>   {
> -    return s->ops->send(s, id, b);
> +    int val;
> +
> +    sout_StreamLock(s);
> +    val = s->ops->send(s, id, b);
> +    sout_StreamUnlock(s);
> +    return val;
>   }
>   
>   void sout_StreamFlush(sout_stream_t *s, void *id)
>   {
>       if (s->ops->flush != NULL)
> +    {
> +        sout_StreamLock(s);
>           s->ops->flush(s, id);
> +        sout_StreamUnlock(s);
> +    }
>   }
>   
>   int sout_StreamControlVa(sout_stream_t *s, int i_query, va_list args)
>   {
> -    if (s->ops->control == NULL)
> -        return VLC_EGENERIC;
> -    return s->ops->control(s, i_query, args);
> +    int val = VLC_EGENERIC;
> +
> +    if (s->ops->control != NULL)
> +    {
> +        sout_StreamLock(s);
> +        val = s->ops->control(s, i_query, args);
> +        sout_StreamUnlock(s);
> +    }
> +    return val;
>   }
>   
>   /* Destroy a "stream_out" module */
> @@ -823,6 +856,7 @@ static sout_stream_t *sout_StreamNew( vlc_object_t *parent, char *psz_name,
>       if (unlikely(priv == NULL))
>           return NULL;
>   
> +    vlc_mutex_init(&priv->lock);
>       p_stream = &priv->stream;
>       p_stream->psz_name = psz_name;
>       p_stream->p_cfg    = p_cfg;
> -- 
> 2.28.0
> 
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