cc/scheduler/scheduler_state

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This source file includes following definitions.
needs_back_to_back_readback_
OutputSurfaceStateToString
BeginImplFrameStateToString
CommitStateToString
TextureStateToString
SynchronousReadbackStateToString
ForcedRedrawOnTimeoutStateToString
ActionToString
AsValue
AdvanceCurrentFrameNumber
HasSentBeginMainFrameThisFrame
HasUpdatedVisibleTilesThisFrame
HasSwappedThisFrame
PendingDrawsShouldBeAborted
PendingActivationsShouldBeForced
ShouldBeginOutputSurfaceCreation
ShouldDraw
ShouldAcquireLayerTexturesForMainThread
ShouldActivatePendingTree
ShouldUpdateVisibleTiles
ShouldSendBeginMainFrame
ShouldCommit
ShouldManageTiles
NextAction
CheckInvariants
UpdateState
UpdateStateOnCommit
UpdateStateOnActivation
UpdateStateOnDraw
UpdateStateOnManageTiles
SetMainThreadNeedsLayerTextures
SetSkipNextBeginMainFrameToReduceLatency
BeginImplFrameNeeded
ShouldPollForAnticipatedDrawTriggers
SupportsProactiveBeginImplFrame
BeginImplFrameNeededToDraw
ProactiveBeginImplFrameWanted
OnBeginImplFrame
OnBeginImplFrameDeadlinePending
OnBeginImplFrameDeadline
OnBeginImplFrameIdle
ShouldTriggerBeginImplFrameDeadlineEarly
MainThreadIsInHighLatencyMode
DidEnterPollForAnticipatedDrawTriggers
DidLeavePollForAnticipatedDrawTriggers
SetVisible
SetCanDraw
SetNeedsRedraw
SetNeedsManageTiles
SetSwapUsedIncompleteTile
SetSmoothnessTakesPriority
DidDrawIfPossibleCompleted
SetNeedsCommit
SetNeedsForcedCommitForReadback
NotifyReadyToCommit
BeginMainFrameAborted
DidManageTiles
DidLoseOutputSurface
NotifyReadyToActivate
DidCreateAndInitializeOutputSurface
NotifyBeginMainFrameStarted
HasInitializedOutputSurface
// Copyright 2011 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 "cc/scheduler/scheduler_state_machine.h"

#include "base/debug/trace_event.h"
#include "base/format_macros.h"
#include "base/logging.h"
#include "base/strings/stringprintf.h"
#include "base/values.h"
#include "ui/gfx/frame_time.h"

namespace cc {

SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
    : settings_(settings),
      output_surface_state_(OUTPUT_SURFACE_LOST),
      begin_impl_frame_state_(BEGIN_IMPL_FRAME_STATE_IDLE),
      commit_state_(COMMIT_STATE_IDLE),
      texture_state_(LAYER_TEXTURE_STATE_UNLOCKED),
      forced_redraw_state_(FORCED_REDRAW_STATE_IDLE),
      readback_state_(READBACK_STATE_IDLE),
      commit_count_(0),
      current_frame_number_(0),
      last_frame_number_swap_performed_(-1),
      last_frame_number_begin_main_frame_sent_(-1),
      last_frame_number_update_visible_tiles_was_called_(-1),
      manage_tiles_funnel_(0),
      consecutive_checkerboard_animations_(0),
      needs_redraw_(false),
      needs_manage_tiles_(false),
      swap_used_incomplete_tile_(false),
      needs_commit_(false),
      main_thread_needs_layer_textures_(false),
      inside_poll_for_anticipated_draw_triggers_(false),
      visible_(false),
      can_start_(false),
      can_draw_(false),
      has_pending_tree_(false),
      pending_tree_is_ready_for_activation_(false),
      active_tree_needs_first_draw_(false),
      draw_if_possible_failed_(false),
      did_create_and_initialize_first_output_surface_(false),
      smoothness_takes_priority_(false),
      skip_next_begin_main_frame_to_reduce_latency_(false),
      skip_begin_main_frame_to_reduce_latency_(false),
      continuous_painting_(false),
      needs_back_to_back_readback_(false) {}

const char* SchedulerStateMachine::OutputSurfaceStateToString(
    OutputSurfaceState state) {
  switch (state) {
    case OUTPUT_SURFACE_ACTIVE:
      return "OUTPUT_SURFACE_ACTIVE";
    case OUTPUT_SURFACE_LOST:
      return "OUTPUT_SURFACE_LOST";
    case OUTPUT_SURFACE_CREATING:
      return "OUTPUT_SURFACE_CREATING";
    case OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT:
      return "OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT";
    case OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION:
      return "OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::BeginImplFrameStateToString(
    BeginImplFrameState state) {
  switch (state) {
    case BEGIN_IMPL_FRAME_STATE_IDLE:
      return "BEGIN_IMPL_FRAME_STATE_IDLE";
    case BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING:
      return "BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING";
    case BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME:
      return "BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME";
    case BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE:
      return "BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::CommitStateToString(CommitState state) {
  switch (state) {
    case COMMIT_STATE_IDLE:
      return "COMMIT_STATE_IDLE";
    case COMMIT_STATE_BEGIN_MAIN_FRAME_SENT:
      return "COMMIT_STATE_BEGIN_MAIN_FRAME_SENT";
    case COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED:
      return "COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED";
    case COMMIT_STATE_READY_TO_COMMIT:
      return "COMMIT_STATE_READY_TO_COMMIT";
    case COMMIT_STATE_WAITING_FOR_ACTIVATION:
      return "COMMIT_STATE_WAITING_FOR_ACTIVATION";
    case COMMIT_STATE_WAITING_FOR_FIRST_DRAW:
      return "COMMIT_STATE_WAITING_FOR_FIRST_DRAW";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::TextureStateToString(TextureState state) {
  switch (state) {
    case LAYER_TEXTURE_STATE_UNLOCKED:
      return "LAYER_TEXTURE_STATE_UNLOCKED";
    case LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD:
      return "LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD";
    case LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD:
      return "LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::SynchronousReadbackStateToString(
    SynchronousReadbackState state) {
  switch (state) {
    case READBACK_STATE_IDLE:
      return "READBACK_STATE_IDLE";
    case READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME:
      return "READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME";
    case READBACK_STATE_WAITING_FOR_COMMIT:
      return "READBACK_STATE_WAITING_FOR_COMMIT";
    case READBACK_STATE_WAITING_FOR_ACTIVATION:
      return "READBACK_STATE_WAITING_FOR_ACTIVATION";
    case READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK:
      return "READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK";
    case READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT:
      return "READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT";
    case READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION:
      return "READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::ForcedRedrawOnTimeoutStateToString(
    ForcedRedrawOnTimeoutState state) {
  switch (state) {
    case FORCED_REDRAW_STATE_IDLE:
      return "FORCED_REDRAW_STATE_IDLE";
    case FORCED_REDRAW_STATE_WAITING_FOR_COMMIT:
      return "FORCED_REDRAW_STATE_WAITING_FOR_COMMIT";
    case FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION:
      return "FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION";
    case FORCED_REDRAW_STATE_WAITING_FOR_DRAW:
      return "FORCED_REDRAW_STATE_WAITING_FOR_DRAW";
  }
  NOTREACHED();
  return "???";
}

const char* SchedulerStateMachine::ActionToString(Action action) {
  switch (action) {
    case ACTION_NONE:
      return "ACTION_NONE";
    case ACTION_SEND_BEGIN_MAIN_FRAME:
      return "ACTION_SEND_BEGIN_MAIN_FRAME";
    case ACTION_COMMIT:
      return "ACTION_COMMIT";
    case ACTION_UPDATE_VISIBLE_TILES:
      return "ACTION_UPDATE_VISIBLE_TILES";
    case ACTION_ACTIVATE_PENDING_TREE:
      return "ACTION_ACTIVATE_PENDING_TREE";
    case ACTION_DRAW_AND_SWAP_IF_POSSIBLE:
      return "ACTION_DRAW_AND_SWAP_IF_POSSIBLE";
    case ACTION_DRAW_AND_SWAP_FORCED:
      return "ACTION_DRAW_AND_SWAP_FORCED";
    case ACTION_DRAW_AND_SWAP_ABORT:
      return "ACTION_DRAW_AND_SWAP_ABORT";
    case ACTION_DRAW_AND_READBACK:
      return "ACTION_DRAW_AND_READBACK";
    case ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
      return "ACTION_BEGIN_OUTPUT_SURFACE_CREATION";
    case ACTION_ACQUIRE_LAYER_TEXTURES_FOR_MAIN_THREAD:
      return "ACTION_ACQUIRE_LAYER_TEXTURES_FOR_MAIN_THREAD";
    case ACTION_MANAGE_TILES:
      return "ACTION_MANAGE_TILES";
  }
  NOTREACHED();
  return "???";
}

scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
  scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue);

  scoped_ptr<base::DictionaryValue> major_state(new base::DictionaryValue);
  major_state->SetString("next_action", ActionToString(NextAction()));
  major_state->SetString("begin_impl_frame_state",
                         BeginImplFrameStateToString(begin_impl_frame_state_));
  major_state->SetString("commit_state", CommitStateToString(commit_state_));
  major_state->SetString("texture_state_",
                         TextureStateToString(texture_state_));
  major_state->SetString("output_surface_state_",
                         OutputSurfaceStateToString(output_surface_state_));
  major_state->SetString(
      "forced_redraw_state",
      ForcedRedrawOnTimeoutStateToString(forced_redraw_state_));
  major_state->SetString("readback_state",
                         SynchronousReadbackStateToString(readback_state_));
  state->Set("major_state", major_state.release());

  scoped_ptr<base::DictionaryValue> timestamps_state(new base::DictionaryValue);
  base::TimeTicks now = gfx::FrameTime::Now();
  timestamps_state->SetDouble(
      "0_interval",
      last_begin_impl_frame_args_.interval.InMicroseconds() / 1000.0L);
  timestamps_state->SetDouble(
      "1_now_to_deadline",
      (last_begin_impl_frame_args_.deadline - now).InMicroseconds() / 1000.0L);
  timestamps_state->SetDouble(
      "2_frame_time_to_now",
      (now - last_begin_impl_frame_args_.frame_time).InMicroseconds() /
          1000.0L);
  timestamps_state->SetDouble(
      "3_frame_time_to_deadline",
      (last_begin_impl_frame_args_.deadline -
              last_begin_impl_frame_args_.frame_time).InMicroseconds() /
          1000.0L);
  timestamps_state->SetDouble(
      "4_now", (now - base::TimeTicks()).InMicroseconds() / 1000.0L);
  timestamps_state->SetDouble(
      "5_frame_time",
      (last_begin_impl_frame_args_.frame_time - base::TimeTicks())
              .InMicroseconds() /
          1000.0L);
  timestamps_state->SetDouble(
      "6_deadline",
      (last_begin_impl_frame_args_.deadline - base::TimeTicks())
              .InMicroseconds() /
          1000.0L);
  state->Set("major_timestamps_in_ms", timestamps_state.release());

  scoped_ptr<base::DictionaryValue> minor_state(new base::DictionaryValue);
  minor_state->SetInteger("commit_count", commit_count_);
  minor_state->SetInteger("current_frame_number", current_frame_number_);

  minor_state->SetInteger("last_frame_number_swap_performed",
                          last_frame_number_swap_performed_);
  minor_state->SetInteger(
      "last_frame_number_begin_main_frame_sent",
      last_frame_number_begin_main_frame_sent_);
  minor_state->SetInteger(
      "last_frame_number_update_visible_tiles_was_called",
      last_frame_number_update_visible_tiles_was_called_);

  minor_state->SetInteger("manage_tiles_funnel", manage_tiles_funnel_);
  minor_state->SetInteger("consecutive_checkerboard_animations",
                          consecutive_checkerboard_animations_);
  minor_state->SetBoolean("needs_redraw", needs_redraw_);
  minor_state->SetBoolean("needs_manage_tiles", needs_manage_tiles_);
  minor_state->SetBoolean("swap_used_incomplete_tile",
                          swap_used_incomplete_tile_);
  minor_state->SetBoolean("needs_commit", needs_commit_);
  minor_state->SetBoolean("main_thread_needs_layer_textures",
                          main_thread_needs_layer_textures_);
  minor_state->SetBoolean("visible", visible_);
  minor_state->SetBoolean("can_start", can_start_);
  minor_state->SetBoolean("can_draw", can_draw_);
  minor_state->SetBoolean("has_pending_tree", has_pending_tree_);
  minor_state->SetBoolean("pending_tree_is_ready_for_activation",
                          pending_tree_is_ready_for_activation_);
  minor_state->SetBoolean("active_tree_needs_first_draw",
                          active_tree_needs_first_draw_);
  minor_state->SetBoolean("draw_if_possible_failed", draw_if_possible_failed_);
  minor_state->SetBoolean("did_create_and_initialize_first_output_surface",
                          did_create_and_initialize_first_output_surface_);
  minor_state->SetBoolean("smoothness_takes_priority",
                          smoothness_takes_priority_);
  minor_state->SetBoolean("main_thread_is_in_high_latency_mode",
                          MainThreadIsInHighLatencyMode());
  minor_state->SetBoolean("skip_begin_main_frame_to_reduce_latency",
                          skip_begin_main_frame_to_reduce_latency_);
  minor_state->SetBoolean("skip_next_begin_main_frame_to_reduce_latency",
                          skip_next_begin_main_frame_to_reduce_latency_);
  minor_state->SetBoolean("continuous_painting", continuous_painting_);
  state->Set("minor_state", minor_state.release());

  return state.PassAs<base::Value>();
}

void SchedulerStateMachine::AdvanceCurrentFrameNumber() {
  current_frame_number_++;

  // "Drain" the ManageTiles funnel.
  if (manage_tiles_funnel_ > 0)
    manage_tiles_funnel_--;

  skip_begin_main_frame_to_reduce_latency_ =
      skip_next_begin_main_frame_to_reduce_latency_;
  skip_next_begin_main_frame_to_reduce_latency_ = false;
}

bool SchedulerStateMachine::HasSentBeginMainFrameThisFrame() const {
  return current_frame_number_ ==
         last_frame_number_begin_main_frame_sent_;
}

bool SchedulerStateMachine::HasUpdatedVisibleTilesThisFrame() const {
  return current_frame_number_ ==
         last_frame_number_update_visible_tiles_was_called_;
}

bool SchedulerStateMachine::HasSwappedThisFrame() const {
  return current_frame_number_ == last_frame_number_swap_performed_;
}

bool SchedulerStateMachine::PendingDrawsShouldBeAborted() const {
  // These are all the cases where we normally cannot or do not want to draw
  // but, if needs_redraw_ is true and we do not draw to make forward progress,
  // we might deadlock with the main thread.
  // This should be a superset of PendingActivationsShouldBeForced() since
  // activation of the pending tree is blocked by drawing of the active tree and
  // the main thread might be blocked on activation of the most recent commit.
  if (PendingActivationsShouldBeForced())
    return true;

  // Impl thread should not draw anymore when texture is acquired by main thread
  // because texture is controlled under main thread.
  if (texture_state_ == LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD)
    return true;

  // Additional states where we should abort draws.
  // Note: We don't force activation in these cases because doing so would
  // result in checkerboarding on resize, becoming visible, etc.
  if (!can_draw_)
    return true;
  if (!visible_)
    return true;
  return false;
}

bool SchedulerStateMachine::PendingActivationsShouldBeForced() const {
  // These are all the cases where, if we do not force activations to make
  // forward progress, we might deadlock with the main thread.

  // There is no output surface to trigger our activations.
  if (output_surface_state_ == OUTPUT_SURFACE_LOST)
    return true;

  return false;
}

bool SchedulerStateMachine::ShouldBeginOutputSurfaceCreation() const {
  // Don't try to initialize too early.
  if (!can_start_)
    return false;

  // We only want to start output surface initialization after the
  // previous commit is complete.
  if (commit_state_ != COMMIT_STATE_IDLE)
    return false;

  // Make sure the BeginImplFrame from any previous OutputSurfaces
  // are complete before creating the new OutputSurface.
  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_IDLE)
    return false;

  // We want to clear the pipline of any pending draws and activations
  // before starting output surface initialization. This allows us to avoid
  // weird corner cases where we abort draws or force activation while we
  // are initializing the output surface and can potentially have a pending
  // readback.
  if (active_tree_needs_first_draw_ || has_pending_tree_)
    return false;

  // We need to create the output surface if we don't have one and we haven't
  // started creating one yet.
  return output_surface_state_ == OUTPUT_SURFACE_LOST;
}

bool SchedulerStateMachine::ShouldDraw() const {
  // After a readback, make sure not to draw again until we've replaced the
  // readback commit with a real one.
  if (readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT ||
      readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION)
    return false;

  // Draw immediately for readbacks to unblock the main thread quickly.
  if (readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK)
    return true;

  // If we need to abort draws, we should do so ASAP since the draw could
  // be blocking other important actions (like output surface initialization),
  // from occuring. If we are waiting for the first draw, then perfom the
  // aborted draw to keep things moving. If we are not waiting for the first
  // draw however, we don't want to abort for no reason.
  if (PendingDrawsShouldBeAborted())
    return active_tree_needs_first_draw_;

  // After this line, we only want to swap once per frame.
  if (HasSwappedThisFrame())
    return false;

  // Except for the cases above, do not draw outside of the BeginImplFrame
  // deadline.
  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
    return false;

  // Only handle forced redraws due to timeouts on the regular deadline.
  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
    return true;

  return needs_redraw_;
}

bool SchedulerStateMachine::ShouldAcquireLayerTexturesForMainThread() const {
  if (!main_thread_needs_layer_textures_)
    return false;
  if (texture_state_ == LAYER_TEXTURE_STATE_UNLOCKED)
    return true;
  DCHECK_EQ(texture_state_, LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD);
  return false;
}

bool SchedulerStateMachine::ShouldActivatePendingTree() const {
  // There is nothing to activate.
  if (!has_pending_tree_)
    return false;

  // We should not activate a second tree before drawing the first one.
  // Even if we need to force activation of the pending tree, we should abort
  // drawing the active tree first.
  if (active_tree_needs_first_draw_)
    return false;

  // If we want to force activation, do so ASAP.
  if (PendingActivationsShouldBeForced())
    return true;

  // At this point, only activate if we are ready to activate.
  return pending_tree_is_ready_for_activation_;
}

bool SchedulerStateMachine::ShouldUpdateVisibleTiles() const {
  if (!settings_.impl_side_painting)
    return false;
  if (HasUpdatedVisibleTilesThisFrame())
    return false;

  // There's no reason to check for tiles if we don't have an output surface.
  if (!HasInitializedOutputSurface())
    return false;

  // We should not check for visible tiles until we've entered the deadline so
  // we check as late as possible and give the tiles more time to initialize.
  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
    return false;

  // If the last swap drew with checkerboard or missing tiles, we should
  // poll for any new visible tiles so we can be notified to draw again
  // when there are.
  if (swap_used_incomplete_tile_)
    return true;

  return false;
}

bool SchedulerStateMachine::ShouldSendBeginMainFrame() const {
  if (!needs_commit_)
    return false;

  // Only send BeginMainFrame when there isn't another commit pending already.
  if (commit_state_ != COMMIT_STATE_IDLE)
    return false;

  // Don't send BeginMainFrame early if we are prioritizing the active tree
  // because of smoothness_takes_priority.
  if (smoothness_takes_priority_ &&
      (has_pending_tree_ || active_tree_needs_first_draw_)) {
    return false;
  }

  // We want to handle readback commits immediately to unblock the main thread.
  // Note: This BeginMainFrame will correspond to the replacement commit that
  // comes after the readback commit itself, so we only send the BeginMainFrame
  // if a commit isn't already pending behind the readback.
  if (readback_state_ == READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME)
    return !CommitPending();

  // We do not need commits if we are not visible, unless there's a
  // request for a readback.
  if (!visible_)
    return false;

  // We want to start the first commit after we get a new output surface ASAP.
  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT)
    return true;

  // We should not send BeginMainFrame while we are in
  // BEGIN_IMPL_FRAME_STATE_IDLE since we might have new
  // user input arriving soon.
  // TODO(brianderson): Allow sending BeginMainFrame while idle when the main
  // thread isn't consuming user input.
  if (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_IDLE &&
      BeginImplFrameNeeded())
    return false;

  // We need a new commit for the forced redraw. This honors the
  // single commit per interval because the result will be swapped to screen.
  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT)
    return true;

  // After this point, we only start a commit once per frame.
  if (HasSentBeginMainFrameThisFrame())
    return false;

  // We shouldn't normally accept commits if there isn't an OutputSurface.
  if (!HasInitializedOutputSurface())
    return false;

  if (skip_begin_main_frame_to_reduce_latency_)
    return false;

  return true;
}

bool SchedulerStateMachine::ShouldCommit() const {
  if (commit_state_ != COMMIT_STATE_READY_TO_COMMIT)
    return false;

  // We must not finish the commit until the pending tree is free.
  if (has_pending_tree_) {
    DCHECK(settings_.main_frame_before_activation_enabled);
    return false;
  }

  // Prioritize drawing the previous commit before finishing the next commit.
  if (active_tree_needs_first_draw_)
    return false;

  return true;
}

bool SchedulerStateMachine::ShouldManageTiles() const {
  // ManageTiles only really needs to be called immediately after commit
  // and then periodically after that. Use a funnel to make sure we average
  // one ManageTiles per BeginImplFrame in the long run.
  if (manage_tiles_funnel_ > 0)
    return false;

  // Limiting to once per-frame is not enough, since we only want to
  // manage tiles _after_ draws. Polling for draw triggers and
  // begin-frame are mutually exclusive, so we limit to these two cases.
  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE &&
      !inside_poll_for_anticipated_draw_triggers_)
    return false;
  return needs_manage_tiles_;
}

SchedulerStateMachine::Action SchedulerStateMachine::NextAction() const {
  if (ShouldAcquireLayerTexturesForMainThread())
    return ACTION_ACQUIRE_LAYER_TEXTURES_FOR_MAIN_THREAD;
  if (ShouldUpdateVisibleTiles())
    return ACTION_UPDATE_VISIBLE_TILES;
  if (ShouldActivatePendingTree())
    return ACTION_ACTIVATE_PENDING_TREE;
  if (ShouldCommit())
    return ACTION_COMMIT;
  if (ShouldDraw()) {
    if (readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK)
      return ACTION_DRAW_AND_READBACK;
    else if (PendingDrawsShouldBeAborted())
      return ACTION_DRAW_AND_SWAP_ABORT;
    else if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
      return ACTION_DRAW_AND_SWAP_FORCED;
    else
      return ACTION_DRAW_AND_SWAP_IF_POSSIBLE;
  }
  if (ShouldManageTiles())
    return ACTION_MANAGE_TILES;
  if (ShouldSendBeginMainFrame())
    return ACTION_SEND_BEGIN_MAIN_FRAME;
  if (ShouldBeginOutputSurfaceCreation())
    return ACTION_BEGIN_OUTPUT_SURFACE_CREATION;
  return ACTION_NONE;
}

void SchedulerStateMachine::CheckInvariants() {
  // We should never try to perform a draw for readback and forced draw due to
  // timeout simultaneously.
  DCHECK(!(forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW &&
           readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK));

  // Main thread should never have the texture locked when there is a pending
  // tree or active tree is not drawn for the first time.
  if (has_pending_tree_ || active_tree_needs_first_draw_)
    DCHECK(texture_state_ != LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD);
}

void SchedulerStateMachine::UpdateState(Action action) {
  switch (action) {
    case ACTION_NONE:
      return;

    case ACTION_UPDATE_VISIBLE_TILES:
      last_frame_number_update_visible_tiles_was_called_ =
          current_frame_number_;
      return;

    case ACTION_ACTIVATE_PENDING_TREE:
      UpdateStateOnActivation();
      return;

    case ACTION_SEND_BEGIN_MAIN_FRAME:
      DCHECK(!has_pending_tree_ ||
             settings_.main_frame_before_activation_enabled);
      DCHECK(!active_tree_needs_first_draw_ ||
             settings_.main_frame_before_draw_enabled);
      DCHECK(visible_ ||
             readback_state_ == READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME);
      commit_state_ = COMMIT_STATE_BEGIN_MAIN_FRAME_SENT;
      needs_commit_ = false;
      if (readback_state_ == READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME)
        readback_state_ = READBACK_STATE_WAITING_FOR_COMMIT;
      last_frame_number_begin_main_frame_sent_ =
          current_frame_number_;
      return;

    case ACTION_COMMIT: {
      bool commit_was_aborted = false;
      UpdateStateOnCommit(commit_was_aborted);
      return;
    }

    case ACTION_DRAW_AND_SWAP_FORCED:
    case ACTION_DRAW_AND_SWAP_IF_POSSIBLE: {
      bool did_swap = true;
      UpdateStateOnDraw(did_swap);
      return;
    }

    case ACTION_DRAW_AND_SWAP_ABORT:
    case ACTION_DRAW_AND_READBACK: {
      bool did_swap = false;
      UpdateStateOnDraw(did_swap);
      return;
    }

    case ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
      DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_LOST);
      output_surface_state_ = OUTPUT_SURFACE_CREATING;

      // The following DCHECKs make sure we are in the proper quiescent state.
      // The pipeline should be flushed entirely before we start output
      // surface creation to avoid complicated corner cases.
      DCHECK_EQ(commit_state_, COMMIT_STATE_IDLE);
      DCHECK(!has_pending_tree_);
      DCHECK(!active_tree_needs_first_draw_);
      return;

    case ACTION_ACQUIRE_LAYER_TEXTURES_FOR_MAIN_THREAD:
      texture_state_ = LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD;
      main_thread_needs_layer_textures_ = false;
      return;

    case ACTION_MANAGE_TILES:
      UpdateStateOnManageTiles();
      return;
  }
}

void SchedulerStateMachine::UpdateStateOnCommit(bool commit_was_aborted) {
  commit_count_++;

  if (commit_was_aborted || settings_.main_frame_before_activation_enabled) {
    commit_state_ = COMMIT_STATE_IDLE;
  } else if (settings_.main_frame_before_draw_enabled) {
    commit_state_ = settings_.impl_side_painting
                        ? COMMIT_STATE_WAITING_FOR_ACTIVATION
                        : COMMIT_STATE_IDLE;
  } else {
    commit_state_ = COMMIT_STATE_WAITING_FOR_FIRST_DRAW;
  }

  // If we are impl-side-painting but the commit was aborted, then we behave
  // mostly as if we are not impl-side-painting since there is no pending tree.
  has_pending_tree_ = settings_.impl_side_painting && !commit_was_aborted;

  // Update state related to readbacks.
  if (readback_state_ == READBACK_STATE_WAITING_FOR_COMMIT) {
    // Update the state if this is the readback commit.
    readback_state_ = has_pending_tree_
                          ? READBACK_STATE_WAITING_FOR_ACTIVATION
                          : READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK;
  } else if (readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT) {
    // Update the state if this is the commit replacing the readback commit.
    readback_state_ = has_pending_tree_
                          ? READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION
                          : READBACK_STATE_IDLE;
  } else {
    DCHECK(readback_state_ == READBACK_STATE_IDLE);
  }

  // Readbacks can interrupt output surface initialization and forced draws,
  // so we do not want to advance those states if we are in the middle of a
  // readback. Note: It is possible for the readback's replacement commit to
  // be the output surface's first commit and/or the forced redraw's commit.
  if (readback_state_ == READBACK_STATE_IDLE ||
      readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION) {
    // Update state related to forced draws.
    if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT) {
      forced_redraw_state_ = has_pending_tree_
                                 ? FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION
                                 : FORCED_REDRAW_STATE_WAITING_FOR_DRAW;
    }

    // Update the output surface state.
    DCHECK_NE(output_surface_state_,
              OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION);
    if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT) {
      if (has_pending_tree_) {
        output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION;
      } else {
        output_surface_state_ = OUTPUT_SURFACE_ACTIVE;
        needs_redraw_ = true;
      }
    }
  }

  // Update state if we have a new active tree to draw, or if the active tree
  // was unchanged but we need to do a readback or forced draw.
  if (!has_pending_tree_ &&
      (!commit_was_aborted ||
       readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK ||
       forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)) {
    needs_redraw_ = true;
    active_tree_needs_first_draw_ = true;
  }

  // This post-commit work is common to both completed and aborted commits.
  pending_tree_is_ready_for_activation_ = false;

  if (draw_if_possible_failed_)
    last_frame_number_swap_performed_ = -1;

  // If we are planing to draw with the new commit, lock the layer textures for
  // use on the impl thread. Otherwise, leave them unlocked.
  if (has_pending_tree_ || needs_redraw_)
    texture_state_ = LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD;
  else
    texture_state_ = LAYER_TEXTURE_STATE_UNLOCKED;

  if (continuous_painting_)
    needs_commit_ = true;
}

void SchedulerStateMachine::UpdateStateOnActivation() {
  if (commit_state_ == COMMIT_STATE_WAITING_FOR_ACTIVATION)
    commit_state_ = COMMIT_STATE_IDLE;

  if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION)
    output_surface_state_ = OUTPUT_SURFACE_ACTIVE;

  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_ACTIVATION)
    forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_DRAW;

  if (readback_state_ == READBACK_STATE_WAITING_FOR_ACTIVATION) {
    readback_state_ = READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK;
  } else if (readback_state_ ==
             READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION) {
    if (needs_back_to_back_readback_) {
      if (commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_SENT) {
        // If main_frame_before_activation_enabled is true, it is possible that
        // we will have already sent the BeginMainFrame here.
        readback_state_ = READBACK_STATE_WAITING_FOR_COMMIT;
      } else {
        // Replacement commit for incoming forced commit should be scheduled
        // after current commit's draw & swap is finished.
        needs_commit_ = true;
        readback_state_ = READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME;
      }
      needs_back_to_back_readback_ = false;
    } else {
      readback_state_ = READBACK_STATE_IDLE;
    }
  }

  has_pending_tree_ = false;
  pending_tree_is_ready_for_activation_ = false;
  active_tree_needs_first_draw_ = true;
  needs_redraw_ = true;
}

void SchedulerStateMachine::UpdateStateOnDraw(bool did_swap) {
  DCHECK(readback_state_ != READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT &&
         readback_state_ != READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION)
      << *AsValue();

  if (readback_state_ == READBACK_STATE_WAITING_FOR_DRAW_AND_READBACK) {
    // The draw corresponds to a readback commit.
    // We are blocking commits from the main thread until after this draw, so
    // we should not have a pending tree.
    DCHECK(!has_pending_tree_);
    // We transition to COMMIT_STATE_BEGIN_MAIN_FRAME_SENT because there is a
    // pending BeginMainFrame behind the readback request.
    commit_state_ = COMMIT_STATE_BEGIN_MAIN_FRAME_SENT;
    readback_state_ = READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT;
  } else if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW) {
    forced_redraw_state_ = FORCED_REDRAW_STATE_IDLE;
  }

  if (commit_state_ == COMMIT_STATE_WAITING_FOR_FIRST_DRAW)
    commit_state_ = COMMIT_STATE_IDLE;

  if (texture_state_ == LAYER_TEXTURE_STATE_ACQUIRED_BY_IMPL_THREAD)
    texture_state_ = LAYER_TEXTURE_STATE_UNLOCKED;

  needs_redraw_ = false;
  draw_if_possible_failed_ = false;
  active_tree_needs_first_draw_ = false;

  if (did_swap)
    last_frame_number_swap_performed_ = current_frame_number_;
}

void SchedulerStateMachine::UpdateStateOnManageTiles() {
  needs_manage_tiles_ = false;
}

void SchedulerStateMachine::SetMainThreadNeedsLayerTextures() {
  DCHECK(!main_thread_needs_layer_textures_);
  DCHECK_NE(texture_state_, LAYER_TEXTURE_STATE_ACQUIRED_BY_MAIN_THREAD);
  main_thread_needs_layer_textures_ = true;
}

void SchedulerStateMachine::SetSkipNextBeginMainFrameToReduceLatency() {
  skip_next_begin_main_frame_to_reduce_latency_ = true;
}

bool SchedulerStateMachine::BeginImplFrameNeeded() const {
  // Proactive BeginImplFrames are bad for the synchronous compositor because we
  // have to draw when we get the BeginImplFrame and could end up drawing many
  // duplicate frames if our new frame isn't ready in time.
  // To poll for state with the synchronous compositor without having to draw,
  // we rely on ShouldPollForAnticipatedDrawTriggers instead.
  if (!SupportsProactiveBeginImplFrame())
    return BeginImplFrameNeededToDraw();

  return BeginImplFrameNeededToDraw() ||
         ProactiveBeginImplFrameWanted();
}

bool SchedulerStateMachine::ShouldPollForAnticipatedDrawTriggers() const {
  // ShouldPollForAnticipatedDrawTriggers is what we use in place of
  // ProactiveBeginImplFrameWanted when we are using the synchronous
  // compositor.
  if (!SupportsProactiveBeginImplFrame()) {
    return !BeginImplFrameNeededToDraw() &&
           ProactiveBeginImplFrameWanted();
  }

  // Non synchronous compositors should rely on
  // ProactiveBeginImplFrameWanted to poll for state instead.
  return false;
}

bool SchedulerStateMachine::SupportsProactiveBeginImplFrame() const {
  // Both the synchronous compositor and disabled vsync settings
  // make it undesirable to proactively request BeginImplFrames.
  // If this is true, the scheduler should poll.
  return !settings_.using_synchronous_renderer_compositor &&
         settings_.throttle_frame_production;
}

// These are the cases where we definitely (or almost definitely) have a
// new frame to draw and can draw.
bool SchedulerStateMachine::BeginImplFrameNeededToDraw() const {
  // The output surface is the provider of BeginImplFrames, so we are not going
  // to get them even if we ask for them.
  if (!HasInitializedOutputSurface())
    return false;

  // If we can't draw, don't tick until we are notified that we can draw again.
  if (!can_draw_)
    return false;

  // The forced draw respects our normal draw scheduling, so we need to
  // request a BeginImplFrame for it.
  if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW)
    return true;

  // There's no need to produce frames if we are not visible.
  if (!visible_)
    return false;

  // We need to draw a more complete frame than we did the last BeginImplFrame,
  // so request another BeginImplFrame in anticipation that we will have
  // additional visible tiles.
  if (swap_used_incomplete_tile_)
    return true;

  return needs_redraw_;
}

// These are cases where we are very likely to draw soon, but might not
// actually have a new frame to draw when we receive the next BeginImplFrame.
// Proactively requesting the BeginImplFrame helps hide the round trip latency
// of the SetNeedsBeginImplFrame request that has to go to the Browser.
bool SchedulerStateMachine::ProactiveBeginImplFrameWanted() const {
  // The output surface is the provider of BeginImplFrames,
  // so we are not going to get them even if we ask for them.
  if (!HasInitializedOutputSurface())
    return false;

  // Do not be proactive when invisible.
  if (!visible_)
    return false;

  // We should proactively request a BeginImplFrame if a commit is pending
  // because we will want to draw if the commit completes quickly.
  if (needs_commit_ || commit_state_ != COMMIT_STATE_IDLE)
    return true;

  // If the pending tree activates quickly, we'll want a BeginImplFrame soon
  // to draw the new active tree.
  if (has_pending_tree_)
    return true;

  // Changing priorities may allow us to activate (given the new priorities),
  // which may result in a new frame.
  if (needs_manage_tiles_)
    return true;

  // If we just swapped, it's likely that we are going to produce another
  // frame soon. This helps avoid negative glitches in our
  // SetNeedsBeginImplFrame requests, which may propagate to the BeginImplFrame
  // provider and get sampled at an inopportune time, delaying the next
  // BeginImplFrame.
  if (last_frame_number_swap_performed_ == current_frame_number_)
    return true;

  return false;
}

void SchedulerStateMachine::OnBeginImplFrame(const BeginFrameArgs& args) {
  AdvanceCurrentFrameNumber();
  last_begin_impl_frame_args_ = args;
  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_IDLE) << *AsValue();
  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING;
}

void SchedulerStateMachine::OnBeginImplFrameDeadlinePending() {
  DCHECK_EQ(begin_impl_frame_state_,
            BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING)
      << *AsValue();
  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME;
}

void SchedulerStateMachine::OnBeginImplFrameDeadline() {
  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME)
      << *AsValue();
  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE;
}

void SchedulerStateMachine::OnBeginImplFrameIdle() {
  DCHECK_EQ(begin_impl_frame_state_, BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE)
      << *AsValue();
  begin_impl_frame_state_ = BEGIN_IMPL_FRAME_STATE_IDLE;
}

bool SchedulerStateMachine::ShouldTriggerBeginImplFrameDeadlineEarly() const {
  // TODO(brianderson): This should take into account multiple commit sources.

  // If we are in the middle of the readback, we won't swap, so there is
  // no reason to trigger the deadline early.
  if (readback_state_ != READBACK_STATE_IDLE)
    return false;

  if (begin_impl_frame_state_ != BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME)
    return false;

  // If we've lost the output surface, end the current BeginImplFrame ASAP
  // so we can start creating the next output surface.
  if (output_surface_state_ == OUTPUT_SURFACE_LOST)
    return true;

  if (active_tree_needs_first_draw_)
    return true;

  if (!needs_redraw_)
    return false;

  // This is used to prioritize impl-thread draws when the main thread isn't
  // producing anything, e.g., after an aborted commit. We also check that we
  // don't have a pending tree -- otherwise we should give it a chance to
  // activate.
  // TODO(skyostil): Revisit this when we have more accurate deadline estimates.
  if (commit_state_ == COMMIT_STATE_IDLE && !has_pending_tree_)
    return true;

  // Prioritize impl-thread draws in smoothness mode.
  if (smoothness_takes_priority_)
    return true;

  return false;
}

bool SchedulerStateMachine::MainThreadIsInHighLatencyMode() const {
  // If a commit is pending before the previous commit has been drawn, we
  // are definitely in a high latency mode.
  if (CommitPending() && (active_tree_needs_first_draw_ || has_pending_tree_))
    return true;

  // If we just sent a BeginMainFrame and haven't hit the deadline yet, the main
  // thread is in a low latency mode.
  if (last_frame_number_begin_main_frame_sent_ == current_frame_number_ &&
      (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_BEGIN_FRAME_STARTING ||
       begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_BEGIN_FRAME))
    return false;

  // If there's a commit in progress it must either be from the previous frame
  // or it started after the impl thread's deadline. In either case the main
  // thread is in high latency mode.
  if (commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_SENT ||
      commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED ||
      commit_state_ == COMMIT_STATE_READY_TO_COMMIT)
    return true;

  // Similarly, if there's a pending tree the main thread is in high latency
  // mode, because either
  //   it's from the previous frame
  // or
  //   we're currently drawing the active tree and the pending tree will thus
  //   only be drawn in the next frame.
  if (has_pending_tree_)
    return true;

  if (begin_impl_frame_state_ == BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE) {
    // Even if there's a new active tree to draw at the deadline or we've just
    // drawn it, it may have been triggered by a previous BeginImplFrame, in
    // which case the main thread is in a high latency mode.
    return (active_tree_needs_first_draw_ ||
            last_frame_number_swap_performed_ == current_frame_number_) &&
           last_frame_number_begin_main_frame_sent_ != current_frame_number_;
  }

  // If the active tree needs its first draw in any other state, we know the
  // main thread is in a high latency mode.
  return active_tree_needs_first_draw_;
}

void SchedulerStateMachine::DidEnterPollForAnticipatedDrawTriggers() {
  AdvanceCurrentFrameNumber();
  inside_poll_for_anticipated_draw_triggers_ = true;
}

void SchedulerStateMachine::DidLeavePollForAnticipatedDrawTriggers() {
  inside_poll_for_anticipated_draw_triggers_ = false;
}

void SchedulerStateMachine::SetVisible(bool visible) { visible_ = visible; }

void SchedulerStateMachine::SetCanDraw(bool can_draw) { can_draw_ = can_draw; }

void SchedulerStateMachine::SetNeedsRedraw() { needs_redraw_ = true; }

void SchedulerStateMachine::SetNeedsManageTiles() {
  if (!needs_manage_tiles_) {
    TRACE_EVENT0("cc",
                 "SchedulerStateMachine::SetNeedsManageTiles");
    needs_manage_tiles_ = true;
  }
}

void SchedulerStateMachine::SetSwapUsedIncompleteTile(
    bool used_incomplete_tile) {
  swap_used_incomplete_tile_ = used_incomplete_tile;
}

void SchedulerStateMachine::SetSmoothnessTakesPriority(
    bool smoothness_takes_priority) {
  smoothness_takes_priority_ = smoothness_takes_priority;
}

void SchedulerStateMachine::DidDrawIfPossibleCompleted(
    DrawSwapReadbackResult::DrawResult result) {
  switch (result) {
    case DrawSwapReadbackResult::INVALID_RESULT:
      NOTREACHED() << "Uninitialized DrawSwapReadbackResult.";
      break;
    case DrawSwapReadbackResult::DRAW_ABORTED_CANT_DRAW:
    case DrawSwapReadbackResult::DRAW_ABORTED_CANT_READBACK:
    case DrawSwapReadbackResult::DRAW_ABORTED_CONTEXT_LOST:
      NOTREACHED() << "Invalid return value from DrawAndSwapIfPossible:"
                   << result;
      break;
    case DrawSwapReadbackResult::DRAW_SUCCESS:
      consecutive_checkerboard_animations_ = 0;
      forced_redraw_state_ = FORCED_REDRAW_STATE_IDLE;
      break;
    case DrawSwapReadbackResult::DRAW_ABORTED_CHECKERBOARD_ANIMATIONS:
      needs_redraw_ = true;

      // If we're already in the middle of a redraw, we don't need to
      // restart it.
      if (forced_redraw_state_ != FORCED_REDRAW_STATE_IDLE)
        return;

      needs_commit_ = true;
      consecutive_checkerboard_animations_++;
      if (settings_.timeout_and_draw_when_animation_checkerboards &&
          consecutive_checkerboard_animations_ >=
              settings_.maximum_number_of_failed_draws_before_draw_is_forced_) {
        consecutive_checkerboard_animations_ = 0;
        // We need to force a draw, but it doesn't make sense to do this until
        // we've committed and have new textures.
        forced_redraw_state_ = FORCED_REDRAW_STATE_WAITING_FOR_COMMIT;
      }
      break;
    case DrawSwapReadbackResult::DRAW_ABORTED_MISSING_HIGH_RES_CONTENT:
      // It's not clear whether this missing content is because of missing
      // pictures (which requires a commit) or because of memory pressure
      // removing textures (which might not).  To be safe, request a commit
      // anyway.
      needs_commit_ = true;
      break;
  }
}

void SchedulerStateMachine::SetNeedsCommit() { needs_commit_ = true; }

void SchedulerStateMachine::SetNeedsForcedCommitForReadback() {
  // If this is called in READBACK_STATE_IDLE, this is a "first" readback
  // request.
  // If this is called in READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT, this
  // is a back-to-back readback request that started before the replacement
  // commit had a chance to land.
  // If this is called in READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION,
  // this is a readback-commit-readback request when replacement commit is in
  // impl-side painting.
  DCHECK(readback_state_ == READBACK_STATE_IDLE ||
         readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT ||
         readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION);

  if (readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_ACTIVATION) {
    // If new forced commit is requested when impl-side painting of replacement
    // commit is in progress, it should not interrupt the draw & swap of current
    // commit(replacement commit). New commit(incoming forced commit) should be
    // started after current commit is finished.
    needs_back_to_back_readback_ = true;
  } else if (commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_SENT) {
    // If there is already a commit in progress when we get the readback request
    // then we don't need to send a BeginMainFrame for the replacement commit,
    // since there's already a BeginMainFrame behind the readback request. In
    // that case, we can skip READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME and go
    // directly to READBACK_STATE_WAITING_FOR_COMMIT.
    readback_state_ = READBACK_STATE_WAITING_FOR_COMMIT;
  } else {
    // Set needs_commit_ to true to trigger scheduling BeginMainFrame().
    needs_commit_ = true;
    readback_state_ = READBACK_STATE_NEEDS_BEGIN_MAIN_FRAME;
  }
}

void SchedulerStateMachine::NotifyReadyToCommit() {
  DCHECK(commit_state_ == COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED) << *AsValue();
  commit_state_ = COMMIT_STATE_READY_TO_COMMIT;
}

void SchedulerStateMachine::BeginMainFrameAborted(bool did_handle) {
  DCHECK_EQ(commit_state_, COMMIT_STATE_BEGIN_MAIN_FRAME_SENT);
  if (did_handle) {
    bool commit_was_aborted = true;
    UpdateStateOnCommit(commit_was_aborted);
  } else {
    DCHECK_NE(readback_state_, READBACK_STATE_WAITING_FOR_COMMIT);
    commit_state_ = COMMIT_STATE_IDLE;
    SetNeedsCommit();
  }
}

void SchedulerStateMachine::DidManageTiles() {
  needs_manage_tiles_ = false;
  // "Fill" the ManageTiles funnel.
  manage_tiles_funnel_++;
}

void SchedulerStateMachine::DidLoseOutputSurface() {
  if (output_surface_state_ == OUTPUT_SURFACE_LOST ||
      output_surface_state_ == OUTPUT_SURFACE_CREATING)
    return;
  output_surface_state_ = OUTPUT_SURFACE_LOST;
  needs_redraw_ = false;
}

void SchedulerStateMachine::NotifyReadyToActivate() {
  if (has_pending_tree_)
    pending_tree_is_ready_for_activation_ = true;
}

void SchedulerStateMachine::DidCreateAndInitializeOutputSurface() {
  DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_CREATING);
  output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT;

  if (did_create_and_initialize_first_output_surface_) {
    // TODO(boliu): See if we can remove this when impl-side painting is always
    // on. Does anything on the main thread need to update after recreate?
    needs_commit_ = true;
  }
  did_create_and_initialize_first_output_surface_ = true;
}

void SchedulerStateMachine::NotifyBeginMainFrameStarted() {
  DCHECK_EQ(commit_state_, COMMIT_STATE_BEGIN_MAIN_FRAME_SENT);

  DCHECK(readback_state_ == READBACK_STATE_IDLE ||
         readback_state_ == READBACK_STATE_WAITING_FOR_COMMIT ||
         readback_state_ == READBACK_STATE_WAITING_FOR_REPLACEMENT_COMMIT);

  commit_state_ = COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED;
}

bool SchedulerStateMachine::HasInitializedOutputSurface() const {
  switch (output_surface_state_) {
    case OUTPUT_SURFACE_LOST:
    case OUTPUT_SURFACE_CREATING:
      return false;

    case OUTPUT_SURFACE_ACTIVE:
    case OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT:
    case OUTPUT_SURFACE_WAITING_FOR_FIRST_ACTIVATION:
      return true;
  }
  NOTREACHED();
  return false;
}

}  // namespace cc
/* [<][>][^][v][top][bottom][index][help] */
root/cc/scheduler/scheduler_state_machine.cc

DEFINITIONS
