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, 3 insertions, 0 deletions

diff --git a/player/main.c b/player/main.c
index 06b1867ebe..b5d019db81 100644
--- a/player/main.c
+++ b/player/main.c
@@ -222,6 +222,7 @@ void mp_destroy(struct MPContext *mpctx)
         pthread_detach(pthread_self());
 
     mp_msg_uninit(mpctx->global);
+    pthread_mutex_destroy(&mpctx->ass_lock);
     talloc_free(mpctx);
 }
 
@@ -329,6 +330,8 @@ struct MPContext *mp_create(void)
         .playback_abort = mp_cancel_new(mpctx),
     };
 
+    pthread_mutex_init(&mpctx->ass_lock, NULL);
+
     mpctx->global = talloc_zero(mpctx, struct mpv_global);
 
     // Nothing must call mp_msg*() and related before this