[FFmpeg-devel] [PATCH] pthread_frame: save the FF_DEBUG_THREADS option in FrameThreadContext.

[Wan-Teh Chang]

Add the debug_threads boolean field to FrameThreadContext. The
debug_threads field records whether the FF_DEBUG_THREADS bit is set in
the debug field of the avctx passed to ff_frame_thread_init(). The
debug_threads field is set when avcodec_open2() is called, never changes
thereafter, and applies to all the decoding threads owned by a
FrameThreadContext. The current code allows different decoding threads
to have different FF_DEBUG_THREADS options, but that does not seem
useful.

This fixes the tsan warning that
2e664b9c1e73c80aab91070c1eb7676f04bdd12d attempted to fix:

WARNING: ThreadSanitizer: data race (pid=452658)
  Write of size 4 at 0x7b640003f4fc by main thread (mutexes: write M248499):
    #0 update_context_from_user [..]/libavcodec/pthread_frame.c:335:19 (5ab42bb1a6f4b068d7863dabe9b2bacc+0xe73859)
[..]
  Previous read of size 4 at 0x7b640003f4fc by thread T130 (mutexes: write M248502, write M248500):
    #0 ff_thread_await_progress [..]/libavcodec/pthread_frame.c:591:26 (5ab42bb1a6f4b068d7863dabe9b2bacc+0xe749a1)

Signed-off-by: Wan-Teh Chang <wtc at google.com>
---
 libavcodec/pthread_frame.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index 363b139f71..eb4d2d9458 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -133,6 +133,7 @@ typedef struct FrameThreadContext {
                                     * Set for the first N packets, where N is the number of threads.
                                     * While it is set, ff_thread_en/decode_frame won't return any results.
                                     */
+    int debug_threads;             ///< Set if the FF_DEBUG_THREADS option is set.
 } FrameThreadContext;
 
 #define THREAD_SAFE_CALLBACKS(avctx) \
@@ -566,7 +567,7 @@ 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)
+    if (p->parent->debug_threads)
         av_log(f->owner[field], AV_LOG_DEBUG,
                "%p finished %d field %d\n", progress, n, field);
 
@@ -588,7 +589,7 @@ 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)
+    if (p->parent->debug_threads)
         av_log(f->owner[field], AV_LOG_DEBUG,
                "thread awaiting %d field %d from %p\n", n, field, progress);
     while (atomic_load_explicit(&progress[field], memory_order_relaxed) < n)
@@ -763,6 +764,7 @@ int ff_frame_thread_init(AVCodecContext *avctx)
 
     fctx->async_lock = 1;
     fctx->delaying = 1;
+    fctx->debug_threads = (avctx->debug & FF_DEBUG_THREADS) != 0;
 
     for (i = 0; i < thread_count; i++) {
         AVCodecContext *copy = av_malloc(sizeof(AVCodecContext));
-- 
2.13.2.725.g09c95d1e9-goog