HW Video: Make media::VideoFrame handle the sync point of the compositor as well as webgl

media/base/video_frame.cc

Index: media/base/video_frame.cc
diff --git a/media/base/video_frame.cc b/media/base/video_frame.cc
index 64e898987d5d213e51f8cc90ef3ecf8bfda1dda2..3c382847a52bd9a36e74fc60b2385b92777434e1 100644
--- a/media/base/video_frame.cc
+++ b/media/base/video_frame.cc
@@ -106,6 +106,9 @@ scoped_refptr<VideoFrame> VideoFrame::WrapNativeTexture(
   frame->mailbox_holder_ = mailbox_holder.Pass();
   frame->mailbox_holder_release_cb_ = mailbox_holder_release_cb;
   frame->read_pixels_cb_ = read_pixels_cb;
+#ifndef NDEBUG
+  frame->debug_initial_sync_point_ = frame->mailbox_holder_->sync_point;
+#endif
 
   return frame;
 }
@@ -406,6 +409,9 @@ VideoFrame::VideoFrame(VideoFrame::Format format,
       coded_size_(coded_size),
       visible_rect_(visible_rect),
       natural_size_(natural_size),
+#ifndef NDEBUG
+      debug_initial_sync_point_(0),
+#endif
       shared_memory_handle_(base::SharedMemory::NULLHandle()),
       timestamp_(timestamp),
       end_of_stream_(end_of_stream) {
@@ -415,8 +421,21 @@ VideoFrame::VideoFrame(VideoFrame::Format format,
 
 VideoFrame::~VideoFrame() {
   if (!mailbox_holder_release_cb_.is_null()) {
-    base::ResetAndReturn(&mailbox_holder_release_cb_)
-        .Run(mailbox_holder_.Pass());
+    std::vector<uint32> release_sync_points;
+    {
+      base::AutoLock locker(release_sync_point_lock_);

[Ami GONE FROM CHROMIUM, 2014/04/11 20:55:17]

locking in a dtor is a code-smell.  If anything can race with the dtor then
losing the race means it will read deleted memory.

Since VideoFrame is RefCountedThreadSafe I believe this lock (and the swap
below) is unnecessary.

[dshwang, 2014/04/22 19:16:51]

I reserve this code as I explained.
IMO ensuring thread visibility via piggy-back is more difficult to maintain.

+      release_sync_points_.swap(release_sync_points);
+    }
+#ifndef NDEBUG
+    // VideoFrame doesn't use |mailbox_holder_->sync_point| as release sync
+    // point because VideoFrame can have multiple clients. i.e. the compositor,
+    // webgl. So VideoFrame uses |release_sync_points_| unlike webgl.
+    // mailbox_holder_->sync_point must be not changed by clients.
+    DCHECK_EQ(debug_initial_sync_point_, mailbox_holder_->sync_point);

[Ami GONE FROM CHROMIUM, 2014/04/11 20:55:17]

This would be even easier to guarantee if nobody had the ability to modify
mailbox_holder_->sync_point, which would be the case if mailbox_holder() died. 
Can you delete that accessor in favor of direct (const!) accessors to
*mailbox_holder_'s members?

Then debug_initial_sync_point_ would no longer be needed (assuming I'm right
about l.436 below also being deletable because it's enforcing a contract that
nobody guarantees).

[dshwang, 2014/04/22 19:16:51]

That's good idea. I make mailbox_holder const. And this change requires changing
VideoFrame ctor little bit.

+    for (size_t i = 0; i < release_sync_points.size(); i++)
+      DCHECK_NE(debug_initial_sync_point_, release_sync_points[i]);

[Ami GONE FROM CHROMIUM, 2014/04/11 20:55:17]

What guarantees that wrap-around doesn't hit this?

+#endif
+    base::ResetAndReturn(&mailbox_holder_release_cb_).Run(release_sync_points);
   }
   if (!no_longer_needed_cb_.is_null())
     base::ResetAndReturn(&no_longer_needed_cb_).Run();
@@ -497,6 +516,14 @@ base::SharedMemoryHandle VideoFrame::shared_memory_handle() const {
   return shared_memory_handle_;
 }
 
+void VideoFrame::AppendReleaseSyncPoint(uint32 sync_point) {
+  DCHECK_EQ(format_, NATIVE_TEXTURE);
+  if (!sync_point)

[Ami GONE FROM CHROMIUM, 2014/04/11 20:55:17]

OOC where does it say that a sync_point of zero means "no sync point"?
(I'm a relative n00b to the world of mailboxes)

[danakj, 2014/04/14 13:19:31]

Hm, it's a convention we follow to return 0 when we want to say "didn't use it,
just use the old sync point"

Maybe we should add this to
./gpu/GLES2/extensions/CHROMIUM/CHROMIUM_sync_point.txt

[dshwang, 2014/04/22 19:16:51]

Thank you for kind explanation. I agree, so I reserve this code.

+    return;
+  base::AutoLock locker(release_sync_point_lock_);
+  release_sync_points_.push_back(sync_point);
+}
+
 void VideoFrame::HashFrameForTesting(base::MD5Context* context) {
   for (int plane = 0; plane < kMaxPlanes; ++plane) {
     if (!IsValidPlane(plane))