[FFmpeg-cvslog] r20254 - trunk/libavcodec/mlpdec.c

[Reimar Döffinger]

On Fri, Oct 16, 2009 at 06:10:00PM +0200, ramiro wrote:
> Author: ramiro
> Date: Fri Oct 16 18:10:00 2009
> New Revision: 20254
> 
> Log:
> mlp: Only initialize VLC tables once. This caused a crash when multiple
> instances of the decoder were started at different times.

Why? I don't think it should.
init_vlc_sparse already does this with the following check:
> if (vlc->table_size && vlc->table_size == vlc->table_allocated)
>     return 0;

Unfortunately with this it still seems possible that two threads end up
in "build_table" at the same time, which that one does not seem to be
designed for (in order to be thread-safe, it may not write any of the
static memory locations more than once).

>  static av_cold void init_static(void)
>  {
> +    if (!huff_vlc[0].bits) {

In addition this is just wrong since huff_vlc[0].bits is certainly not
written last in build_table, thus this might end up with the second
decoder skipping the initialization despite the initialization not
having finished.

>      INIT_VLC_STATIC(&huff_vlc[0], VLC_BITS, 18,
>                  &ff_mlp_huffman_tables[0][0][1], 2, 1,
>                  &ff_mlp_huffman_tables[0][0][0], 2, 1, 512);

Just try adding a sleep(1000); or so here and you'll see it very easily.