[FFmpeg-cvslog] pthread_frame: make accesses to debug field be protected by owner lock.

[Ronald S. Bultje]

ffmpeg | branch: master | Ronald S. Bultje <rsbultje at gmail.com> | Thu Apr  6 13:58:59 2017 -0400| [2e664b9c1e73c80aab91070c1eb7676f04bdd12d] | committer: Ronald S. Bultje

pthread_frame: make accesses to debug field be protected by owner lock.

The av_log() is done outside the lock, but this way the accesses to the
field (reads and writes) are always protected by a mutex. The av_log()
is not run inside the lock context because it may involve user callbacks
and doing that in performance-sensitive code is probably not a good idea.

This should fix occasional tsan warnings when running fate-h264, like:

WARNING: ThreadSanitizer: data race (pid=10916)
  Write of size 4 at 0x7d64000174fc by main thread (mutexes: write M2313):
    #0 update_context_from_user src/libavcodec/pthread_frame.c:335 (ffmpeg+0x000000df7b06)
[..]
  Previous read of size 4 at 0x7d64000174fc by thread T1 (mutexes: write M2311):
    #0 ff_thread_await_progress src/libavcodec/pthread_frame.c:592 (ffmpeg+0x000000df8b3e)

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=2e664b9c1e73c80aab91070c1eb7676f04bdd12d
---

 libavcodec/pthread_frame.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index aaf576d..46c6292 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -566,12 +566,11 @@ void ff_thread_report_progress(ThreadFrame *f, int n, int field)
 
     p = f->owner[field]->internal->thread_ctx;
 
+    pthread_mutex_lock(&p->progress_mutex);
     if (f->owner[field]->debug&FF_DEBUG_THREADS)
         av_log(f->owner[field], AV_LOG_DEBUG,
                "%p finished %d field %d\n", progress, n, field);
 
-    pthread_mutex_lock(&p->progress_mutex);
-
     atomic_store_explicit(&progress[field], n, memory_order_release);
 
     pthread_cond_broadcast(&p->progress_cond);
@@ -589,11 +588,10 @@ void ff_thread_await_progress(ThreadFrame *f, int n, int field)
 
     p = f->owner[field]->internal->thread_ctx;
 
+    pthread_mutex_lock(&p->progress_mutex);
     if (f->owner[field]->debug&FF_DEBUG_THREADS)
         av_log(f->owner[field], AV_LOG_DEBUG,
                "thread awaiting %d field %d from %p\n", n, field, progress);
-
-    pthread_mutex_lock(&p->progress_mutex);
     while (atomic_load_explicit(&progress[field], memory_order_relaxed) < n)
         pthread_cond_wait(&p->progress_cond, &p->progress_mutex);
     pthread_mutex_unlock(&p->progress_mutex);