pthread_frame: allow per-field ThreadFrame owners.

This tries to handle cases where separate invocations of decode_frame()
(each running in separate threads) write to respective fields in the
same AVFrame->data[]. Having per-field owners makes interaction between
readers (the referencing thread) and writers (the decoding thread)
slightly more optimal if both accesses are field-based, since they will
use the respective producer's thread objects (mutex/cond) instead of
sharing the thread objects of the first field's producer.

In practice, this fixes the following tsan-warning in fate-h264:

WARNING: ThreadSanitizer: data race (pid=21615)
  Read of size 4 at 0x7d640000d9fc by thread T2 (mutexes: write M1006):
    #0 ff_thread_report_progress pthread_frame.c:569 (ffmpeg:x86_64+0x100f7cf54)
[..]
  Previous write of size 4 at 0x7d640000d9fc by main thread (mutexes: write M1004):
    #0 update_context_from_user pthread_frame.c:335 (ffmpeg:x86_64+0x100f81abb)

1 files changed, 10 insertions, 8 deletions

diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index 9a6b83ac45..c246c2fded 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -564,10 +564,11 @@ void ff_thread_report_progress(ThreadFrame *f, int n, int field)
         atomic_load_explicit(&progress[field], memory_order_relaxed) >= n)
         return;
 
-    p = f->owner->internal->thread_ctx;
+    p = f->owner[field]->internal->thread_ctx;
 
-    if (f->owner->debug&FF_DEBUG_THREADS)
-        av_log(f->owner, AV_LOG_DEBUG, "%p finished %d field %d\n", progress, n, field);
+    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);
 
@@ -586,10 +587,11 @@ void ff_thread_await_progress(ThreadFrame *f, int n, int field)
         atomic_load_explicit(&progress[field], memory_order_acquire) >= n)
         return;
 
-    p = f->owner->internal->thread_ctx;
+    p = f->owner[field]->internal->thread_ctx;
 
-    if (f->owner->debug&FF_DEBUG_THREADS)
-        av_log(f->owner, AV_LOG_DEBUG, "thread awaiting %d field %d from %p\n", n, field, progress);
+    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)
@@ -882,7 +884,7 @@ static int thread_get_buffer_internal(AVCodecContext *avctx, ThreadFrame *f, int
     PerThreadContext *p = avctx->internal->thread_ctx;
     int err;
 
-    f->owner = avctx;
+    f->owner[0] = f->owner[1] = avctx;
 
     ff_init_buffer_info(avctx, f->f);
 
@@ -986,7 +988,7 @@ void ff_thread_release_buffer(AVCodecContext *avctx, ThreadFrame *f)
         av_log(avctx, AV_LOG_DEBUG, "thread_release_buffer called on pic %p\n", f);
 
     av_buffer_unref(&f->progress);
-    f->owner    = NULL;
+    f->owner[0] = f->owner[1] = NULL;
 
     if (can_direct_free) {
         av_frame_unref(f->f);