cc: Implement deadline scheduling disabled by default

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 72bade39070fff948f572591b4917c95aaf00f89..8ffd575a7b06eddf18d18271570c4b5cc2d1a720 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -4,6 +4,7 @@
 
 #include "cc/scheduler/scheduler.h"
 
+#include <algorithm>
 #include "base/auto_reset.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ -21,12 +22,10 @@ Scheduler::Scheduler(SchedulerClient* client,
       inside_process_scheduled_actions_(false),
       inside_action_(SchedulerStateMachine::ACTION_NONE) {
   DCHECK(client_);
-  DCHECK(!state_machine_.BeginFrameNeededToDrawByImplThread());
+  DCHECK(!state_machine_.BeginFrameNeededByImplThread());
 }
 
-Scheduler::~Scheduler() {
-  client_->SetNeedsBeginFrameOnImplThread(false);
-}
+Scheduler::~Scheduler() {}
 
 void Scheduler::SetCanStart() {
   state_machine_.SetCanStart();
@@ -48,6 +47,12 @@ void Scheduler::NotifyReadyToActivate() {
   ProcessScheduledActions();
 }
 
+void Scheduler::ActivatePendingTree() {
+  client_->ScheduledActionActivatePendingTree();
+  if (state_machine_.ShouldTriggerBeginFrameDeadlineEarly())
+    PostBeginFrameDeadline(base::TimeTicks());
+}
+
 void Scheduler::SetNeedsCommit() {
   state_machine_.SetNeedsCommit();
   ProcessScheduledActions();
@@ -84,6 +89,9 @@ void Scheduler::FinishCommit() {
   TRACE_EVENT0("cc", "Scheduler::FinishCommit");
   state_machine_.FinishCommit();
   ProcessScheduledActions();
+
+  if (state_machine_.ShouldTriggerBeginFrameDeadlineEarly())
+    PostBeginFrameDeadline(base::TimeTicks());
 }
 
 void Scheduler::BeginFrameAbortedByMainThread(bool did_handle) {
@@ -94,14 +102,17 @@ void Scheduler::BeginFrameAbortedByMainThread(bool did_handle) {
 
 void Scheduler::DidLoseOutputSurface() {
   TRACE_EVENT0("cc", "Scheduler::DidLoseOutputSurface");
+  last_set_needs_begin_frame_ = false;
+  begin_frame_deadline_closure_.Cancel();
   state_machine_.DidLoseOutputSurface();
   ProcessScheduledActions();
 }
 
 void Scheduler::DidCreateAndInitializeOutputSurface() {
   TRACE_EVENT0("cc", "Scheduler::DidCreateAndInitializeOutputSurface");
+  DCHECK(!last_set_needs_begin_frame_);
+  DCHECK(begin_frame_deadline_closure_.IsCancelled());
   state_machine_.DidCreateAndInitializeOutputSurface();
-  last_set_needs_begin_frame_ = false;
   ProcessScheduledActions();
 }
 
@@ -112,12 +123,11 @@ base::TimeTicks Scheduler::AnticipatedDrawTime() {
       last_begin_frame_args_.interval <= base::TimeDelta())
     return base::TimeTicks();
 
-  // TODO(brianderson): Express this in terms of the deadline.
   base::TimeTicks now = base::TimeTicks::Now();
-  int64 intervals = 1 + ((now - last_begin_frame_args_.frame_time) /
-                         last_begin_frame_args_.interval);
-  return last_begin_frame_args_.frame_time +
-      (last_begin_frame_args_.interval * intervals);
+  base::TimeTicks timebase = std::max(last_begin_frame_args_.frame_time,
+                                      last_begin_frame_args_.deadline);
+  int64 intervals = 1 + ((now - timebase) / last_begin_frame_args_.interval);
+  return timebase + (last_begin_frame_args_.interval * intervals);
 }
 
 base::TimeTicks Scheduler::LastBeginFrameOnImplThreadTime() {
@@ -125,32 +135,30 @@ base::TimeTicks Scheduler::LastBeginFrameOnImplThreadTime() {
 }
 
 void Scheduler::SetupNextBeginFrameIfNeeded() {
-  bool needs_begin_frame_to_draw =
-      state_machine_.BeginFrameNeededToDrawByImplThread();
-  // We want to avoid proactive begin frames with the synchronous compositor
-  // because every SetNeedsBeginFrame will force a redraw.
-  bool proactive_begin_frame_wanted =
-      state_machine_.ProactiveBeginFrameWantedByImplThread() &&
-      !settings_.using_synchronous_renderer_compositor &&
-      settings_.throttle_frame_production;
-  bool needs_begin_frame = needs_begin_frame_to_draw ||
-                           proactive_begin_frame_wanted;
+  bool needs_begin_frame =
+      state_machine_.BeginFrameNeededByImplThread();
+
+  bool at_end_of_deadline =
+      state_machine_.begin_frame_state() ==
+          SchedulerStateMachine::BEGIN_FRAME_STATE_INSIDE_DEADLINE;
 
   bool should_call_set_needs_begin_frame =
       // Always request the BeginFrame immediately if it wasn't needed before.
       (needs_begin_frame && !last_set_needs_begin_frame_) ||
       // We always need to explicitly request our next BeginFrame.
-      state_machine_.inside_begin_frame();
+      at_end_of_deadline;
 
   if (should_call_set_needs_begin_frame) {
     client_->SetNeedsBeginFrameOnImplThread(needs_begin_frame);
     last_set_needs_begin_frame_ = needs_begin_frame;
   }
 
-  // Setup PollForAnticipatedDrawTriggers for cases where we want a proactive
-  // BeginFrame but aren't requesting one.
-  if (!needs_begin_frame &&
-      state_machine_.ProactiveBeginFrameWantedByImplThread()) {
+  // Setup PollForAnticipatedDrawTriggers if we need to monitor state but
+  // aren't expecting any more BeginFrames. This should only be needed by the
+  // synchronous compositor when BeginFrameNeededByImplThread is false.
+  if (state_machine_.ShouldPollForAnticipatedDrawTriggers()) {
+    DCHECK(settings_.using_synchronous_renderer_compositor);
+    DCHECK(!needs_begin_frame);
     if (poll_for_draw_triggers_closure_.IsCancelled()) {
       poll_for_draw_triggers_closure_.Reset(
           base::Bind(&Scheduler::PollForAnticipatedDrawTriggers,
@@ -167,11 +175,64 @@ void Scheduler::SetupNextBeginFrameIfNeeded() {
 
 void Scheduler::BeginFrame(const BeginFrameArgs& args) {
   TRACE_EVENT0("cc", "Scheduler::BeginFrame");
-  DCHECK(!state_machine_.inside_begin_frame());
+  DCHECK(state_machine_.begin_frame_state() ==
+         SchedulerStateMachine::BEGIN_FRAME_STATE_IDLE);
   last_begin_frame_args_ = args;
-  state_machine_.DidEnterBeginFrame(args);
+  last_begin_frame_args_.deadline -= client_->DrawDurationEstimate();
+  state_machine_.OnBeginFrame(last_begin_frame_args_);
+  ProcessScheduledActions();
+  state_machine_.OnBeginFrameDeadlinePending();
+
+  if (settings_.using_synchronous_renderer_compositor) {
+    // The synchronous renderer compositor has to make its GL calls
+    // within this call to BeginFrame.
+    // TODO(brianderson): Have the OutputSurface initiate the deadline tasks
+    // so the sychronous renderer compoistor can take advantage of splitting
+    // up the BeginFrame and deadline as well.
+    OnBeginFrameDeadline();
+  } else if (!settings_.deadline_scheduling_enabled) {
+    // We emulate the old non-deadline scheduler here by posting the
+    // deadline task without any delay.
+    PostBeginFrameDeadline(base::TimeTicks());
+  } else if (state_machine_.ShouldTriggerBeginFrameDeadlineEarly()) {
+    // We are ready to draw a new active tree immediately.
+    PostBeginFrameDeadline(base::TimeTicks());
+  } else if (state_machine_.needs_redraw()) {
+    // We have an animation or fast input path on the impl thread that wants
+    // to draw, so don't wait too long for a new active tree.
+    PostBeginFrameDeadline(last_begin_frame_args_.deadline);
+  } else {
+    // The impl thread doesn't have anything it wants to draw and we are just
+    // waiting for a new active tree, so post the deadline for the next
+    // expected BeginFrame start. This allows us to draw immediately when
+    // there is a new active tree, instead of waiting for the next BeginFrame.
+    // TODO(brianderson): Handle long deadlines (that are past the next frame's
+    // frame time) properly instead of using this hack.

[Sami, 2013/09/25 13:42:52]

Just curious: was the idea to handle this with a proactive BeginFrame or did you
have something else in mind? Reusing the expired BeginFrame like this is still
likely faster, but might cause trouble on the browser compositor side.

[brianderson, 2013/10/02 11:30:15]

Yes, we would enter this case if a proactive BeginFrame was requested because of
a pending commit, but there were no impl-side animations or input handlers.

This case could cause us to draw after the deadline, but there is no reason to
wait for the next BeginFrame since the result of drawing then will be the same. 
The deadline is pretty fuzzy, so we might still make it in time for the browser
compositor to pick it up and make its own deadline.  If not, the browser
compositor needs to handle cases when the renderer misses its deadline anyway,
in which case we should end up in a high-latency mode if we were previously in a
low-latency mode (and the browser compositor couldn't wait before drawing its
next frame), or a skipped frame if we are already in a high-latency mode.

+    PostBeginFrameDeadline(last_begin_frame_args_.frame_time +
+                           last_begin_frame_args_.interval);
+  }
+}
+
+void Scheduler::PostBeginFrameDeadline(base::TimeTicks deadline) {
+  begin_frame_deadline_closure_.Cancel();
+  begin_frame_deadline_closure_.Reset(
+      base::Bind(&Scheduler::OnBeginFrameDeadline, weak_factory_.GetWeakPtr()));
+  client_->PostBeginFrameDeadline(begin_frame_deadline_closure_.callback(),
+                                  deadline);
+}
+
+void Scheduler::OnBeginFrameDeadline() {
+  TRACE_EVENT0("cc", "Scheduler::OnBeginFrameDeadline");
+  begin_frame_deadline_closure_.Cancel();
+  state_machine_.OnBeginFrameDeadline();
   ProcessScheduledActions();
-  state_machine_.DidLeaveBeginFrame();
+  // We only transition out of BEGIN_FRAME_STATE_INSIDE_DEADLINE when all
+  // actions that occur back-to-back in response to entering
+  // BEGIN_FRAME_STATE_INSIDE_DEADLINE have completed. This is important
+  // because sending the BeginFrame to the main thread will not occur if
+  // we transition to BEGIN_FRAME_STATE_IDLE too early.
+  state_machine_.OnBeginFrameIdle();
+  client_->DidBeginFrameDeadlineOnImplThread();
 }
 
 void Scheduler::PollForAnticipatedDrawTriggers() {
@@ -230,7 +291,7 @@ void Scheduler::ProcessScheduledActions() {
         client_->ScheduledActionUpdateVisibleTiles();
         break;
       case SchedulerStateMachine::ACTION_ACTIVATE_PENDING_TREE:
-        client_->ScheduledActionActivatePendingTree();
+        ActivatePendingTree();
         break;
       case SchedulerStateMachine::ACTION_DRAW_AND_SWAP_IF_POSSIBLE:
         DrawAndSwapIfPossible();