sub: protect ASS_Renderer state

Each subtitle track gets its own decoder instance (sd_ass). But they use
a shared ASS_Renderer. This is done mainly because of fontconfig.
Initializing fontconfig is very slow when using it with memory fonts, so
there's a practical need to cache this memory font state, which is done
by not creating separate ASS_Renderers. This is very dirty and very
evil, but we probably can't get rid of it any time soon.

The shared ASS_Renderer was not properly synchronized. While the program
logic guarantees that only one sd_ass instance is visible at a time,
there are other interactions that require synchronization. In
particular, I suspect concurrent execution of mp_ass_configure_fonts()
and sd_ass.get_bitmaps cause issues in a newer libass development
branch.

So here's a shitty hack that hopefully fixes things, hopefully only
until libass becomes less dependent on fontconfig.

1 files changed, 4 insertions, 1 deletions

diff --git a/player/sub.c b/player/sub.c
index 89da9f719c..548e7b22d9 100644
--- a/player/sub.c
+++ b/player/sub.c
@@ -306,12 +306,15 @@ static void reinit_subdec(struct MPContext *mpctx, struct track *track,
 
     sub_set_video_res(dec_sub, w, h);
     sub_set_video_fps(dec_sub, fps);
-    sub_set_ass_renderer(dec_sub, mpctx->ass_library, mpctx->ass_renderer);
+    sub_set_ass_renderer(dec_sub, mpctx->ass_library, mpctx->ass_renderer,
+                         &mpctx->ass_lock);
     sub_init_from_sh(dec_sub, track->stream);
 
     if (mpctx->ass_renderer) {
+        pthread_mutex_lock(&mpctx->ass_lock);
         mp_ass_configure_fonts(mpctx->ass_renderer, opts->sub_text_style,
                                mpctx->global, mpctx->ass_log);
+        pthread_mutex_unlock(&mpctx->ass_lock);
     }
 
     // Don't do this if the file has video/audio streams. Don't do it even