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, 1 insertions, 0 deletions

diff --git a/player/core.h b/player/core.h
index 907c997b96..7b3e47d8d2 100644
--- a/player/core.h
+++ b/player/core.h
@@ -317,6 +317,7 @@ typedef struct MPContext {
      * loaded across ordered chapters, instead of reloading and rescanning
      * them on each transition. (Both of these objects contain this state.)
      */
+    pthread_mutex_t ass_lock;
     struct ass_renderer *ass_renderer;
     struct ass_library *ass_library;
     struct mp_log *ass_log;