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// 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 <stdint.h>
#include <memory>
#include <string>
#include "base/macros.h"
#include "cc/cc_export.h"
#include "cc/scheduler/commit_earlyout_reason.h"
#include "cc/scheduler/draw_result.h"
#include "cc/scheduler/scheduler_settings.h"
#include "cc/tiles/tile_priority.h"
#include "components/viz/common/frame_sinks/begin_frame_args.h"
namespace base {
namespace trace_event {
class ConvertableToTraceFormat;
class TracedValue;
namespace cc {
enum class ScrollHandlerState {
const char* ScrollHandlerStateToString(ScrollHandlerState state);
// The SchedulerStateMachine decides how to coordinate main thread activites
// like painting/running javascript with rendering and input activities on the
// impl thread.
// The state machine tracks internal state but is also influenced by external
// state. Internal state includes things like whether a frame has been
// requested, while external state includes things like the current time being
// near to the vblank time.
// The scheduler seperates "what to do next" from the updating of its internal
// state to make testing cleaner.
class CC_EXPORT SchedulerStateMachine {
// settings must be valid for the lifetime of this class.
explicit SchedulerStateMachine(const SchedulerSettings& settings);
enum class LayerTreeFrameSinkState {
static const char* LayerTreeFrameSinkStateToString(
LayerTreeFrameSinkState state);
// Note: BeginImplFrameState does not cycle through these states in a fixed
// order on all platforms. It's up to the scheduler to set these correctly.
enum class BeginImplFrameState {
static const char* BeginImplFrameStateToString(BeginImplFrameState state);
// The scheduler uses a deadline to wait for main thread updates before
// submitting a compositor frame. BeginImplFrameDeadlineMode specifies when
// the deadline should run.
enum class BeginImplFrameDeadlineMode {
NONE, // No deadline should be scheduled e.g. for synchronous compositor.
IMMEDIATE, // Deadline should be scheduled to run immediately.
REGULAR, // Deadline should be scheduled to run at the deadline provided by
// in the BeginFrameArgs.
LATE, // Deadline should be scheduled run when the next frame is expected
// to arrive.
BLOCKED, // Deadline should be blocked indefinitely until the next frame
// arrives.
static const char* BeginImplFrameDeadlineModeToString(
BeginImplFrameDeadlineMode mode);
enum class BeginMainFrameState {
static const char* BeginMainFrameStateToString(BeginMainFrameState state);
enum class ForcedRedrawOnTimeoutState {
static const char* ForcedRedrawOnTimeoutStateToString(
ForcedRedrawOnTimeoutState state);
BeginMainFrameState begin_main_frame_state() const {
return begin_main_frame_state_;
bool CommitPending() const {
return begin_main_frame_state_ == BeginMainFrameState::SENT ||
begin_main_frame_state_ == BeginMainFrameState::STARTED ||
begin_main_frame_state_ == BeginMainFrameState::READY_TO_COMMIT;
bool NewActiveTreeLikely() const {
return needs_begin_main_frame_ || CommitPending() || has_pending_tree_;
bool RedrawPending() const { return needs_redraw_; }
bool PrepareTilesPending() const { return needs_prepare_tiles_; }
enum class Action {
static const char* ActionToString(Action action);
std::unique_ptr<base::trace_event::ConvertableToTraceFormat> AsValue() const;
void AsValueInto(base::trace_event::TracedValue* dict) const;
Action NextAction() const;
void WillSendBeginMainFrame();
void WillNotifyBeginMainFrameNotSent();
void WillCommit(bool commit_had_no_updates);
void WillActivate();
void WillDraw();
void WillBeginLayerTreeFrameSinkCreation();
void WillPrepareTiles();
void WillInvalidateLayerTreeFrameSink();
void WillPerformImplSideInvalidation();
void DidDraw(DrawResult draw_result);
void AbortDraw();
// Indicates whether the impl thread needs a BeginImplFrame callback in order
// to make progress.
bool BeginFrameNeeded() const;
// Indicates that the system has entered and left a BeginImplFrame callback.
// The scheduler will not draw more than once in a given BeginImplFrame
// callback nor send more than one BeginMainFrame message.
void OnBeginImplFrame(uint64_t source_id,
uint64_t sequence_number,
bool animate_only);
// Indicates that the scheduler has entered the draw phase. The scheduler
// will not draw more than once in a single draw phase.
// TODO(sunnyps): Rename OnBeginImplFrameDeadline to OnDraw or similar.
void OnBeginImplFrameDeadline();
void OnBeginImplFrameIdle();
int current_frame_number() const { return current_frame_number_; }
BeginImplFrameState begin_impl_frame_state() const {
return begin_impl_frame_state_;
// Returns BeginImplFrameDeadlineMode computed based on current state.
BeginImplFrameDeadlineMode CurrentBeginImplFrameDeadlineMode() const;
// If the main thread didn't manage to produce a new frame in time for the
// impl thread to draw, it is in a high latency mode.
bool main_thread_missed_last_deadline() const {
return main_thread_missed_last_deadline_;
bool IsDrawThrottled() const;
// Indicates whether the LayerTreeHostImpl is visible.
void SetVisible(bool visible);
bool visible() const { return visible_; }
void SetBeginFrameSourcePaused(bool paused);
bool begin_frame_source_paused() const { return begin_frame_source_paused_; }
// Indicates that a redraw is required, either due to the impl tree changing
// or the screen being damaged and simply needing redisplay.
void SetNeedsRedraw();
bool needs_redraw() const { return needs_redraw_; }
bool OnlyImplSideUpdatesExpected() const;
// Indicates that prepare-tiles is required. This guarantees another
// PrepareTiles will occur shortly (even if no redraw is required).
void SetNeedsPrepareTiles();
// If the scheduler attempted to draw, this provides feedback regarding
// whether or not a CompositorFrame was actually submitted. We might skip the
// submitting anything when there is not damage, for example.
void DidSubmitCompositorFrame();
// Notification from the LayerTreeFrameSink that a submitted frame has been
// consumed and it is ready for the next one.
void DidReceiveCompositorFrameAck();
int pending_submit_frames() const { return pending_submit_frames_; }
// Indicates whether to prioritize impl thread latency (i.e., animation
// smoothness) over new content activation.
void SetTreePrioritiesAndScrollState(TreePriority tree_priority,
ScrollHandlerState scroll_handler_state);
// Indicates if the main thread will likely respond within 1 vsync.
void SetCriticalBeginMainFrameToActivateIsFast(bool is_fast);
// A function of SetTreePrioritiesAndScrollState and
// SetCriticalBeginMainFrameToActivateIsFast.
bool ImplLatencyTakesPriority() const;
// Indicates that a new begin main frame flow needs to be performed, either
// to pull updates from the main thread to the impl, or to push deltas from
// the impl thread to main.
void SetNeedsBeginMainFrame();
bool needs_begin_main_frame() const { return needs_begin_main_frame_; }
void SetMainThreadWantsBeginMainFrameNotExpectedMessages(bool new_state);
bool wants_begin_main_frame_not_expected_messages() const {
return wants_begin_main_frame_not_expected_;
// Requests a single impl frame (after the current frame if there is one
// active).
void SetNeedsOneBeginImplFrame();
// Call this only in response to receiving an Action::SEND_BEGIN_MAIN_FRAME
// from NextAction.
// Indicates that all painting is complete.
void NotifyReadyToCommit();
// Call this only in response to receiving an Action::SEND_BEGIN_MAIN_FRAME
// from NextAction if the client rejects the BeginMainFrame message.
void BeginMainFrameAborted(CommitEarlyOutReason reason);
// Indicates production should be skipped to recover latency.
void SetSkipNextBeginMainFrameToReduceLatency(bool skip);
// For Android WebView, resourceless software draws are allowed even when
// invisible.
void SetResourcelessSoftwareDraw(bool resourceless_draw);
// Indicates whether drawing would, at this time, make sense.
// CanDraw can be used to suppress flashes or checkerboarding
// when such behavior would be undesirable.
void SetCanDraw(bool can);
// For Android WebView, indicates that the draw should be skipped because the
// frame sink is not ready to receive frames.
void SetSkipDraw(bool skip);
// Indicates that scheduled BeginMainFrame is started.
void NotifyBeginMainFrameStarted();
// Indicates that the pending tree is ready for activation. Returns whether
// the notification received updated the state for the current pending tree,
// if any.
bool NotifyReadyToActivate();
// Indicates the active tree's visible tiles are ready to be drawn.
void NotifyReadyToDraw();
void SetNeedsImplSideInvalidation(bool needs_first_draw_on_activation);
bool has_pending_tree() const { return has_pending_tree_; }
bool active_tree_needs_first_draw() const {
return active_tree_needs_first_draw_;
void DidPrepareTiles();
void DidLoseLayerTreeFrameSink();
void DidCreateAndInitializeLayerTreeFrameSink();
bool HasInitializedLayerTreeFrameSink() const;
// True if we need to abort draws to make forward progress.
bool PendingDrawsShouldBeAborted() const;
bool CouldSendBeginMainFrame() const;
void SetDeferCommits(bool defer_commits);
void SetVideoNeedsBeginFrames(bool video_needs_begin_frames);
bool video_needs_begin_frames() const { return video_needs_begin_frames_; }
bool did_submit_in_last_frame() const { return did_submit_in_last_frame_; }
bool needs_impl_side_invalidation() const {
return needs_impl_side_invalidation_;
bool previous_pending_tree_was_impl_side() const {
return previous_pending_tree_was_impl_side_;
bool critical_begin_main_frame_to_activate_is_fast() const {
return critical_begin_main_frame_to_activate_is_fast_;
void set_should_defer_invalidation_for_fast_main_frame(bool defer) {
should_defer_invalidation_for_fast_main_frame_ = defer;
bool should_defer_invalidation_for_fast_main_frame() const {
return should_defer_invalidation_for_fast_main_frame_;
bool main_thread_failed_to_respond_last_deadline() const {
return main_thread_failed_to_respond_last_deadline_;
bool BeginFrameRequiredForAction() const;
bool BeginFrameNeededForVideo() const;
bool ProactiveBeginFrameWanted() const;
// Indicates if we should post the deadline to draw immediately. This is true
// when we aren't expecting a commit or activation, or we're prioritizing
// active tree draw (see ImplLatencyTakesPriority()).
bool ShouldTriggerBeginImplFrameDeadlineImmediately() const;
// Indicates if we shouldn't schedule a deadline. Used to defer drawing until
// the entire pipeline is flushed and active tree is ready to draw for
// headless.
bool ShouldBlockDeadlineIndefinitely() const;
bool ShouldPerformImplSideInvalidation() const;
bool CouldCreatePendingTree() const;
bool ShouldDeferInvalidatingForMainFrame() const;
bool ShouldAbortCurrentFrame() const;
bool ShouldBeginLayerTreeFrameSinkCreation() const;
bool ShouldDraw() const;
bool ShouldActivateSyncTree() const;
bool ShouldSendBeginMainFrame() const;
bool ShouldCommit() const;
bool ShouldPrepareTiles() const;
bool ShouldInvalidateLayerTreeFrameSink() const;
bool ShouldNotifyBeginMainFrameNotSent() const;
void WillDrawInternal();
void WillPerformImplSideInvalidationInternal();
void DidDrawInternal(DrawResult draw_result);
const SchedulerSettings settings_;
LayerTreeFrameSinkState layer_tree_frame_sink_state_ =
BeginImplFrameState begin_impl_frame_state_ = BeginImplFrameState::IDLE;
BeginMainFrameState begin_main_frame_state_ = BeginMainFrameState::IDLE;
ForcedRedrawOnTimeoutState forced_redraw_state_ =
// These are used for tracing only.
int commit_count_ = 0;
int current_frame_number_ = 0;
int last_frame_number_submit_performed_ = -1;
int last_frame_number_draw_performed_ = -1;
int last_frame_number_begin_main_frame_sent_ = -1;
int last_frame_number_invalidate_layer_tree_frame_sink_performed_ = -1;
// Inputs from the last impl frame that are required for decisions made in
// this impl frame. The values from the last frame are cached before being
// reset in OnBeginImplFrame.
struct FrameEvents {
bool commit_had_no_updates = false;
bool did_commit_during_frame = false;
FrameEvents last_frame_events_;
// These are used to ensure that an action only happens once per frame,
// deadline, etc.
bool did_draw_ = false;
bool did_send_begin_main_frame_for_current_frame_ = true;
// Initialized to true to prevent begin main frame before begin frames have
// started. Reset to true when we stop asking for begin frames.
bool did_notify_begin_main_frame_not_sent_ = true;
bool did_commit_during_frame_ = false;
bool did_invalidate_layer_tree_frame_sink_ = false;
bool did_perform_impl_side_invalidation_ = false;
bool did_prepare_tiles_ = false;
int consecutive_checkerboard_animations_ = 0;
int pending_submit_frames_ = 0;
int submit_frames_with_current_layer_tree_frame_sink_ = 0;
bool needs_redraw_ = false;
bool needs_prepare_tiles_ = false;
bool needs_begin_main_frame_ = false;
bool needs_one_begin_impl_frame_ = false;
bool visible_ = false;
bool begin_frame_source_paused_ = false;
bool resourceless_draw_ = false;
bool can_draw_ = false;
bool skip_draw_ = false;
bool has_pending_tree_ = false;
bool pending_tree_is_ready_for_activation_ = false;
bool active_tree_needs_first_draw_ = false;
bool did_create_and_initialize_first_layer_tree_frame_sink_ = false;
TreePriority tree_priority_ = NEW_CONTENT_TAKES_PRIORITY;
ScrollHandlerState scroll_handler_state_ =
bool critical_begin_main_frame_to_activate_is_fast_ = true;
bool main_thread_missed_last_deadline_ = false;
bool skip_next_begin_main_frame_to_reduce_latency_ = false;
bool defer_commits_ = false;
bool video_needs_begin_frames_ = false;
bool last_commit_had_no_updates_ = false;
bool active_tree_is_ready_to_draw_ = true;
bool did_draw_in_last_frame_ = false;
bool did_submit_in_last_frame_ = false;
bool needs_impl_side_invalidation_ = false;
bool next_invalidation_needs_first_draw_on_activation_ = false;
bool should_defer_invalidation_for_fast_main_frame_ = true;
bool begin_frame_is_animate_only_ = false;
// Set to true if the main thread fails to respond with a commit or abort the
// main frame before the draw deadline on the previous impl frame.
bool main_thread_failed_to_respond_last_deadline_ = false;
bool previous_pending_tree_was_impl_side_ = false;
bool current_pending_tree_is_impl_side_ = false;
bool wants_begin_main_frame_not_expected_ = false;
// If set to true, the pending tree must be drawn at least once after
// activation before a new tree can be activated.
bool pending_tree_needs_first_draw_on_activation_ = false;
} // namespace cc