[vlc-devel] [PATCH 2/2] Wait-free snapshot handling in the vout thread

[Laurent Aimar]

Hi,

On Wed, Mar 11, 2009, basos g wrote:
> Nice though.
> Why lock twice , though ?
> Couldn't we write something like :
> 
>        /*
>          * Take a snapshot if requested
>          */
> 
>         if( p_directbuffer &&
>             vlc_mutex_trylock( &p_vout->p->snapshot.lock ) )
>         {
>            if ( p_vout->p->snapshot.i_request > 0 )
>           {
>                while( p_vout->p->snapshot.i_request > 0 )
>                {
>                    picture_t *p_pic = picture_New( p_vout->fmt_out.i_chroma,
>                                                    p_vout->fmt_out.i_width,
>                                                    p_vout->fmt_out.i_height,
>                                                    p_vout->fmt_out.i_aspect  );
>                    if( !p_pic )
>                        break;
> 
>                    picture_Copy( p_pic, p_directbuffer );
> 
>                    p_pic->p_next = p_vout->p->snapshot.p_picture;
>                    p_vout->p->snapshot.p_picture = p_pic;
>                    p_vout->p->snapshot.i_request--;
>                } //end while
>                vlc_cond_broadcast( &p_vout->p->snapshot.wait );
>          } //end if i_request>0
>           vlc_mutex_unlock( &p_vout->p->snapshot.lock );
>       } //end if mutext try lock
 No, you cannot, spu_SortSubpictures must be call with the snapshot request
information.
 And it is better to not lock around spu_SortSubpictures with the snapshot lock.

-- 
fenrir