Introduce VideoFrameScheduler{Impl}.

media/filters/video_frame_scheduler_impl.cc

Index: media/filters/video_frame_scheduler_impl.cc
diff --git a/media/filters/video_frame_scheduler_impl.cc b/media/filters/video_frame_scheduler_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..13292ad2a63920fb2935486dff282673e0dd5f50
--- /dev/null
+++ b/media/filters/video_frame_scheduler_impl.cc
@@ -0,0 +1,104 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/filters/video_frame_scheduler_impl.h"
+
+#include "base/single_thread_task_runner.h"
+#include "base/time/default_tick_clock.h"
+#include "media/base/video_frame.h"
+
+namespace media {
+
+VideoFrameSchedulerImpl::VideoFrameSchedulerImpl(
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+    const DisplayCB& display_cb)
+    : task_runner_(task_runner),
+      display_cb_(display_cb),
+      tick_clock_(new base::DefaultTickClock()) {
+}
+
+VideoFrameSchedulerImpl::~VideoFrameSchedulerImpl() {
+}
+
+void VideoFrameSchedulerImpl::ScheduleVideoFrame(
+    const scoped_refptr<VideoFrame>& frame,
+    base::TimeTicks wall_ticks,
+    const DoneCB& done_cb) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  pending_frames_.push(PendingFrame(frame, wall_ticks, done_cb));
+  ResetTimerIfNecessary();
+}
+
+void VideoFrameSchedulerImpl::Reset() {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  while (!pending_frames_.empty()) {
+    pending_frames_.top().done_cb.Run(pending_frames_.top().frame, RESET);
+    pending_frames_.pop();
+  }
+}
+
+void VideoFrameSchedulerImpl::SetTickClockForTesting(
+    scoped_ptr<base::TickClock> tick_clock) {
+  tick_clock_.swap(tick_clock);
+}
+
+void VideoFrameSchedulerImpl::ResetTimerIfNecessary() {
+  if (pending_frames_.empty()) {
+    DCHECK(!timer_.IsRunning());
+    return;
+  }
+
+  timer_.Stop();
+  timer_.Start(FROM_HERE,
+               pending_frames_.top().wall_ticks - tick_clock_->NowTicks(),

[acolwell GONE FROM CHROMIUM, 2014/04/14 21:17:59]

Can't this potentially result in negative delays?

[scherkus (not reviewing), 2014/04/14 21:35:31]

Yep, which results in a PostTask() instead of PostDelayedTask()

will add clarifying comment

+               base::Bind(&VideoFrameSchedulerImpl::OnTimerFired,
+                          base::Unretained(this)));
+}
+
+void VideoFrameSchedulerImpl::OnTimerFired() {
+  base::TimeTicks now = tick_clock_->NowTicks();
+
+  // Move all frames that have reached their deadline into a separate queue.
+  PendingFrameQueue expired_frames;

[acolwell GONE FROM CHROMIUM, 2014/04/14 21:17:59]

nit: This doesn't need to be a priority queue since you are extracting frames in
order.  Using a list here can avoid unnecessary rebalancing and struct copying
below.

[scherkus (not reviewing), 2014/04/14 21:35:31]

Done.

+  while (!pending_frames_.empty() && pending_frames_.top().wall_ticks <= now) {
+    expired_frames.push(pending_frames_.top());
+    pending_frames_.pop();
+  }
+
+  // Signal that all frames except for the last one as dropped.
+  while (expired_frames.size() > 1) {
+    expired_frames.top().done_cb.Run(expired_frames.top().frame, DROPPED);
+    expired_frames.pop();
+  }
+
+  // Display the last expired frame.
+  if (!expired_frames.empty()) {
+    display_cb_.Run(expired_frames.top().frame);
+    expired_frames.top().done_cb.Run(expired_frames.top().frame, DISPLAYED);
+    expired_frames.pop();
+  }
+
+  ResetTimerIfNecessary();
+}
+
+VideoFrameSchedulerImpl::PendingFrame::PendingFrame(
+    const scoped_refptr<VideoFrame>& frame,
+    base::TimeTicks wall_ticks,
+    const DoneCB& done_cb)
+    : frame(frame), wall_ticks(wall_ticks), done_cb(done_cb) {
+}
+
+VideoFrameSchedulerImpl::PendingFrame::~PendingFrame() {
+}
+
+bool VideoFrameSchedulerImpl::PendingFrame::operator<(
+    const PendingFrame& other) const {
+  // Flip the comparison as std::priority_queue<T>::top() returns the largest
+  // element.
+  //
+  // Assume video frames with identical timestamps contain identical content.
+  return wall_ticks > other.wall_ticks;
+}
+
+}  // namespace media