From: Jean-Baptiste Kempf <jb@videolan.org>
Date: Tue, 28 Sep 2021 19:47:40 +0000 (+0200)
Subject: lookahead: Keep b_exit_thread under ifbuf.mutex
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=66a5bc1bd1563d8227d5d18440b525a09bcf17ca;p=libx264

lookahead: Keep b_exit_thread under ifbuf.mutex

The lookahead_thread main loop checks b_exit_thread and exits if it is set.
That flag is set by x264_lookahead_delete, which uses ifbuf.mutex to guard accessing it.
However, the read in the while-loop condition of lookahead_thread is not guarded,
and so TSAN sometimes reports a data race.
---

diff --git a/encoder/lookahead.c b/encoder/lookahead.c
index 18958bd0..93f59b19 100644
--- a/encoder/lookahead.c
+++ b/encoder/lookahead.c
@@ -89,9 +89,14 @@ static void lookahead_slicetype_decide( x264_t *h )
 
 REALIGN_STACK static void *lookahead_thread( x264_t *h )
 {
-    while( !h->lookahead->b_exit_thread )
+    while( 1 )
     {
         x264_pthread_mutex_lock( &h->lookahead->ifbuf.mutex );
+        if( h->lookahead->b_exit_thread )
+        {
+            x264_pthread_mutex_unlock( &h->lookahead->ifbuf.mutex );
+            break;
+        }
         x264_pthread_mutex_lock( &h->lookahead->next.mutex );
         int shift = X264_MIN( h->lookahead->next.i_max_size - h->lookahead->next.i_size, h->lookahead->ifbuf.i_size );
         lookahead_shift( &h->lookahead->next, &h->lookahead->ifbuf, shift );