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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)
This commit is contained in:
Ronald S. Bultje 2017-04-06 13:58:59 -04:00
parent 7f05c5cea0
commit 2e664b9c1e
1 changed files with 2 additions and 4 deletions
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6
libavcodec/pthread_frame.c
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@ -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);