Teach main thread event queue about closures.

content/renderer/input/main_thread_event_queue.cc

 // Copyright 2016 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 "content/renderer/input/main_thread_event_queue.h"
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "content/common/input/event_with_latency_info.h"
 #include "content/common/input_messages.h"
 
 namespace content {
 
 namespace {
 
+const size_t kTenSeconds = 10 * 1000 * 1000;
+
+class QueuedClosure : public QueuedItem {
+ public:
+  QueuedClosure(const base::Closure& closure) : closure_(closure) {}
+
+  ~QueuedClosure() override {}
+
+  bool CanCoalesceWith(const QueuedItem&) override { return false; }
+
+  void CoalesceWith(const QueuedItem&) override { NOTREACHED(); }
+
+  bool IsSameEventClass(const QueuedItem&) const override {
+    // Say they are the same event class as an optimization to
+    // because coalescing will always fail.
+    return true;
+  }
+
+  bool IsEvent() const override { return false; }

[mustaq, 2017/03/24 15:31:18]

I think it would be unwise to consider QueuedClosure as a non-event:
symantically they are events, and treating them as non-events would make all
these misnomers: |main_thread_EVENT_queue|, |web_input_EVENT_queue|,
|same_EVENT_class|, |EVENThandled|..., plus UMA labels!

I suggest this instead: |MainThreadQueueItem| would have two subclasses:
|QueuedEventClosure|, |QueuedWebInputEvent|, and use the member function
|IsWebInputEvent| to distinguish between them. Does it sound reasonable?

[dtapuska, 2017/03/24 20:16:31]

How about a QueuedClosure and a QueuedWebInputEvent... And change IsEvent to
IsWebInputEvent and get rid of the IsSameEventClass... 

+
+  void Dispatch(int routing_id, MainThreadEventQueueClient*) override {
+    closure_.Run();
+  }
+
+  void EventHandled(int routing_id,
+                    blink::scheduler::RendererScheduler* renderer_scheduler,
+                    MainThreadEventQueueClient* client,
+                    blink::WebInputEvent::Type type,
+                    blink::WebInputEventResult result,
+                    InputEventAckState ack_result) override {}
+
+ private:
+  base::Closure closure_;
+};
+
+class EventWithDispatchType : public ScopedWebInputEventWithLatencyInfo,
+                              public QueuedItem {
+ public:
+  EventWithDispatchType(ui::WebScopedInputEvent event,
+                        const ui::LatencyInfo& latency,
+                        InputEventDispatchType dispatch_type,
+                        bool originally_cancelable)
+      : ScopedWebInputEventWithLatencyInfo(std::move(event), latency),
+        dispatch_type_(dispatch_type),
+        non_blocking_coalesced_count_(0),
+        creation_timestamp_(base::TimeTicks::Now()),
+        last_coalesced_timestamp_(creation_timestamp_),
+        originally_cancelable_(originally_cancelable) {}
+
+  ~EventWithDispatchType() override {}
+
+  bool CanCoalesceWith(const QueuedItem& other_item) override {
+    if (!other_item.IsEvent())
+      return false;
+    const EventWithDispatchType& other_event =
+        static_cast<const EventWithDispatchType&>(other_item);
+    return ScopedWebInputEventWithLatencyInfo::CanCoalesceWith(other_event);
+  }
+
+  void CoalesceWith(const QueuedItem& other_item) override {
+    const EventWithDispatchType& other_event =
+        static_cast<const EventWithDispatchType&>(other_item);
+    // If this event was blocking push the event id to the blocking
+    // list before updating the dispatch_type of this event.
+    if (dispatch_type_ == DISPATCH_TYPE_BLOCKING) {
+      blocking_coalesced_event_ids_.push_back(
+          ui::WebInputEventTraits::GetUniqueTouchEventId(event()));
+    } else {
+      non_blocking_coalesced_count_++;
+    }
+    ScopedWebInputEventWithLatencyInfo::CoalesceWith(other_event);
+    dispatch_type_ = other_event.dispatch_type_;
+    last_coalesced_timestamp_ = base::TimeTicks::Now();
+    originally_cancelable_ = other_event.originally_cancelable_;
+  }
+
+  bool IsSameEventClass(const QueuedItem& other_item) const override {
+    if (!other_item.IsEvent())
+      return false;
+    const EventWithDispatchType& other_event =
+        static_cast<const EventWithDispatchType&>(other_item);
+    return event().isSameEventClass(other_event.event());
+  }
+
+  bool IsEvent() const override { return true; }
+
+  void Dispatch(int routing_id, MainThreadEventQueueClient* client) override {
+    // Report the coalesced count only for continuous events; otherwise
+    // the zero value would be dominated by non-continuous events.
+    base::TimeTicks now = base::TimeTicks::Now();
+    if (IsContinuousEvent()) {
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Event.MainThreadEventQueue.Continuous.QueueingTime",
+          (now - creationTimestamp()).InMicroseconds(), 1, kTenSeconds, 50);
+
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Event.MainThreadEventQueue.Continuous.FreshnessTime",
+          (now - lastCoalescedTimestamp()).InMicroseconds(), 1, kTenSeconds,
+          50);
+
+      UMA_HISTOGRAM_COUNTS_1000("Event.MainThreadEventQueue.CoalescedCount",
+                                coalescedCount());
+    } else {
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "Event.MainThreadEventQueue.NonContinuous.QueueingTime",
+          (now - creationTimestamp()).InMicroseconds(), 1, kTenSeconds, 50);
+    }
+
+    InputEventDispatchType dispatch_type = dispatchType();
+    if (!blockingCoalescedEventIds().empty()) {
+      switch (dispatch_type) {
+        case DISPATCH_TYPE_BLOCKING:
+          dispatch_type = DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN;
+          break;
+        case DISPATCH_TYPE_NON_BLOCKING:
+          dispatch_type = DISPATCH_TYPE_NON_BLOCKING_NOTIFY_MAIN;
+          break;
+        default:
+          NOTREACHED();
+      }
+    }
+    client->HandleEventOnMainThread(routing_id, &coalesced_event(),
+                                    latencyInfo(), dispatch_type);
+  }
+
+  void EventHandled(int routing_id,
+                    blink::scheduler::RendererScheduler* renderer_scheduler,
+                    MainThreadEventQueueClient* client,
+                    blink::WebInputEvent::Type type,
+                    blink::WebInputEventResult result,
+                    InputEventAckState ack_result) override {
+    for (const auto id : blockingCoalescedEventIds()) {
+      client->SendInputEventAck(routing_id, type, ack_result, id);
+      if (renderer_scheduler) {
+        renderer_scheduler->DidHandleInputEventOnMainThread(event(), result);
+      }
+    }
+  }
+
+  bool originallyCancelable() const { return originally_cancelable_; }
+
+ private:
+  const std::deque<uint32_t>& blockingCoalescedEventIds() const {
+    return blocking_coalesced_event_ids_;
+  }
+  InputEventDispatchType dispatchType() const { return dispatch_type_; }
+  base::TimeTicks creationTimestamp() const { return creation_timestamp_; }
+  base::TimeTicks lastCoalescedTimestamp() const {
+    return last_coalesced_timestamp_;
+  }
+
+  size_t coalescedCount() const {
+    return non_blocking_coalesced_count_ + blocking_coalesced_event_ids_.size();
+  }
+
+  bool IsContinuousEvent() const {
+    switch (event().type()) {
+      case blink::WebInputEvent::MouseMove:
+      case blink::WebInputEvent::MouseWheel:
+      case blink::WebInputEvent::TouchMove:
+        return true;
+      default:
+        return false;
+    }
+  }
+
+  InputEventDispatchType dispatch_type_;
+
+  // Contains the unique touch event ids to be acked. If
+  // the events are not TouchEvents the values will be 0. More importantly for
+  // those cases the deque ends up containing how many additional ACKs
+  // need to be sent.
+  std::deque<uint32_t> blocking_coalesced_event_ids_;
+  // Contains the number of non-blocking events coalesced.
+  size_t non_blocking_coalesced_count_;
+  base::TimeTicks creation_timestamp_;
+  base::TimeTicks last_coalesced_timestamp_;
+
+  // Whether the received event was originally cancelable or not. The compositor
+  // input handler can change the event based on presence of event handlers so
+  // this is the state at which the renderer received the event from the
+  // browser.
+  bool originally_cancelable_;
+};
+
 // Time interval at which touchmove events will be skipped during rAF signal.
 const base::TimeDelta kAsyncTouchMoveInterval =
     base::TimeDelta::FromMilliseconds(200);
 
-const size_t kTenSeconds = 10 * 1000 * 1000;
-
-bool IsContinuousEvent(const std::unique_ptr<EventWithDispatchType>& event) {
-  switch (event->event().type()) {
-    case blink::WebInputEvent::MouseMove:
-    case blink::WebInputEvent::MouseWheel:
-    case blink::WebInputEvent::TouchMove:
-      return true;
-    default:
-      return false;
-  }
-}
-
-bool IsAsyncTouchMove(const std::unique_ptr<EventWithDispatchType>& event) {
+bool IsAsyncTouchMove(const std::unique_ptr<QueuedItem>& queued_item) {
+  if (!queued_item->IsEvent())
+    return false;
+  const EventWithDispatchType* event =
+      static_cast<const EventWithDispatchType*>(queued_item.get());
   if (event->event().type() != blink::WebInputEvent::TouchMove)
     return false;
   const blink::WebTouchEvent& touch_event =
       static_cast<const blink::WebTouchEvent&>(event->event());
   return touch_event.movedBeyondSlopRegion && !event->originallyCancelable();
 }
 
 }  // namespace
 
-EventWithDispatchType::EventWithDispatchType(
-    ui::WebScopedInputEvent event,
-    const ui::LatencyInfo& latency,
-    InputEventDispatchType dispatch_type,
-    bool originally_cancelable)
-    : ScopedWebInputEventWithLatencyInfo(std::move(event), latency),
-      dispatch_type_(dispatch_type),
-      non_blocking_coalesced_count_(0),
-      creation_timestamp_(base::TimeTicks::Now()),
-      last_coalesced_timestamp_(creation_timestamp_),
-      originally_cancelable_(originally_cancelable) {}
-
-EventWithDispatchType::~EventWithDispatchType() {}
-
-void EventWithDispatchType::CoalesceWith(const EventWithDispatchType& other) {
-  // If this event was blocking push the event id to the blocking
-  // list before updating the dispatch_type of this event.
-  if (dispatch_type_ == DISPATCH_TYPE_BLOCKING) {
-    blocking_coalesced_event_ids_.push_back(
-        ui::WebInputEventTraits::GetUniqueTouchEventId(event()));
-  } else {
-    non_blocking_coalesced_count_++;
-  }
-  ScopedWebInputEventWithLatencyInfo::CoalesceWith(other);
-  dispatch_type_ = other.dispatch_type_;
-  last_coalesced_timestamp_ = base::TimeTicks::Now();
-  originally_cancelable_ = other.originally_cancelable_;
-}
-
 MainThreadEventQueue::SharedState::SharedState()
-    : sent_main_frame_request_(false) {}
+    : sent_main_frame_request_(false), sent_post_task_(false) {}
 
 MainThreadEventQueue::SharedState::~SharedState() {}
 
 MainThreadEventQueue::MainThreadEventQueue(
     int routing_id,
     MainThreadEventQueueClient* client,
     const scoped_refptr<base::SingleThreadTaskRunner>& main_task_runner,
     blink::scheduler::RendererScheduler* renderer_scheduler)
     : routing_id_(routing_id),
       client_(client),
@@ skipping 114 matching lines @@
   std::unique_ptr<EventWithDispatchType> event_with_dispatch_type(
       new EventWithDispatchType(std::move(event), latency, dispatch_type,
                                 originally_cancelable));
 
   QueueEvent(std::move(event_with_dispatch_type));
 
   // send an ack when we are non-blocking.
   return non_blocking;
 }
 
+void MainThreadEventQueue::QueueClosure(const base::Closure& closure) {
+  bool needs_post_task = false;
+  std::unique_ptr<QueuedClosure> item(new QueuedClosure(closure));
+  {
+    base::AutoLock lock(shared_state_lock_);
+    shared_state_.events_.Queue(std::move(item));
+    needs_post_task = !shared_state_.sent_post_task_;
+    shared_state_.sent_post_task_ = true;
+  }
+
+  if (needs_post_task)
+    SendEventNotificationToMainThread();
+}
+
 void MainThreadEventQueue::DispatchInFlightEvent() {
-  if (in_flight_event_) {
-    // Report the coalesced count only for continuous events; otherwise
-    // the zero value would be dominated by non-continuous events.
-    base::TimeTicks now = base::TimeTicks::Now();
-    if (IsContinuousEvent(in_flight_event_)) {
-      UMA_HISTOGRAM_CUSTOM_COUNTS(
-          "Event.MainThreadEventQueue.Continuous.QueueingTime",
-          (now - in_flight_event_->creationTimestamp()).InMicroseconds(), 1,
-          kTenSeconds, 50);
-
-      UMA_HISTOGRAM_CUSTOM_COUNTS(
-          "Event.MainThreadEventQueue.Continuous.FreshnessTime",
-          (now - in_flight_event_->lastCoalescedTimestamp()).InMicroseconds(),
-          1, kTenSeconds, 50);
-
-      UMA_HISTOGRAM_COUNTS_1000("Event.MainThreadEventQueue.CoalescedCount",
-                                in_flight_event_->coalescedCount());
-    } else {
-      UMA_HISTOGRAM_CUSTOM_COUNTS(
-          "Event.MainThreadEventQueue.NonContinuous.QueueingTime",
-          (now - in_flight_event_->creationTimestamp()).InMicroseconds(), 1,
-          kTenSeconds, 50);
-    }
-
-    InputEventDispatchType dispatch_type = in_flight_event_->dispatchType();
-    if (!in_flight_event_->blockingCoalescedEventIds().empty()) {
-      switch (dispatch_type) {
-        case DISPATCH_TYPE_BLOCKING:
-          dispatch_type = DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN;
-          break;
-        case DISPATCH_TYPE_NON_BLOCKING:
-          dispatch_type = DISPATCH_TYPE_NON_BLOCKING_NOTIFY_MAIN;
-          break;
-        default:
-          NOTREACHED();
-      }
-    }
-    client_->HandleEventOnMainThread(
-        routing_id_, &in_flight_event_->coalesced_event(),
-        in_flight_event_->latencyInfo(), dispatch_type);
-  }
+  if (in_flight_event_)
+    in_flight_event_->Dispatch(routing_id_, client_);
 
   in_flight_event_.reset();
 }
 
 void MainThreadEventQueue::PossiblyScheduleMainFrame() {
   if (IsRafAlignedInputDisabled())
     return;
   bool needs_main_frame = false;
   {
     base::AutoLock lock(shared_state_lock_);
     if (!shared_state_.sent_main_frame_request_ &&
         !shared_state_.events_.empty() &&
-        IsRafAlignedEvent(shared_state_.events_.front()->event())) {
+        IsRafAlignedEvent(shared_state_.events_.front())) {
       needs_main_frame = !shared_state_.sent_main_frame_request_;
       shared_state_.sent_main_frame_request_ = false;
     }
   }
   if (needs_main_frame)
     client_->NeedsMainFrame(routing_id_);
 }
 
-void MainThreadEventQueue::DispatchSingleEvent() {
+void MainThreadEventQueue::DispatchEvents() {
+  std::deque<std::unique_ptr<QueuedItem>> events_to_process;
   {
     base::AutoLock lock(shared_state_lock_);
-    if (shared_state_.events_.empty())
-      return;
+    shared_state_.sent_post_task_ = false;
 
-    in_flight_event_ = shared_state_.events_.Pop();
+    shared_state_.events_.swap(&events_to_process);
+
+    // Now take any raf aligned events that are at the tail of the queue
+    // and put them back.
+    while (!events_to_process.empty()) {
+      if (!IsRafAlignedEvent(events_to_process.back()))
+        break;
+      shared_state_.events_.emplace_front(std::move(events_to_process.back()));
+      events_to_process.pop_back();
+    }
   }
-  DispatchInFlightEvent();
+  while (!events_to_process.empty()) {
+    in_flight_event_ = std::move(events_to_process.front());
+    events_to_process.pop_front();
+    DispatchInFlightEvent();
+  }
   PossiblyScheduleMainFrame();
 }
 
 void MainThreadEventQueue::EventHandled(blink::WebInputEvent::Type type,
                                         blink::WebInputEventResult result,
                                         InputEventAckState ack_result) {
   if (in_flight_event_) {
-    for (const auto id : in_flight_event_->blockingCoalescedEventIds()) {
-      client_->SendInputEventAck(routing_id_, type, ack_result, id);
-      if (renderer_scheduler_) {
-        renderer_scheduler_->DidHandleInputEventOnMainThread(
-            in_flight_event_->event(), result);
-      }
-    }
+    in_flight_event_->EventHandled(routing_id_, renderer_scheduler_, client_,
+                                   type, result, ack_result);
   }
 }
 
 void MainThreadEventQueue::DispatchRafAlignedInput(base::TimeTicks frame_time) {
   if (IsRafAlignedInputDisabled())
     return;
 
-  std::deque<std::unique_ptr<EventWithDispatchType>> events_to_process;
+  std::deque<std::unique_ptr<QueuedItem>> events_to_process;
   {
     base::AutoLock lock(shared_state_lock_);
     shared_state_.sent_main_frame_request_ = false;
 
     while (!shared_state_.events_.empty()) {
-      if (!IsRafAlignedEvent(shared_state_.events_.front()->event()))
-        break;
-
-      // Throttle touchmoves that are async.
-      if (handle_raf_aligned_touch_input_ &&
-          IsAsyncTouchMove(shared_state_.events_.front())) {
-        if (shared_state_.events_.size() == 1 &&
-            frame_time < shared_state_.last_async_touch_move_timestamp_ +
-                             kAsyncTouchMoveInterval) {
-          break;
+      if (IsRafAlignedEvent(shared_state_.events_.front())) {
+        // Throttle touchmoves that are async.
+        if (handle_raf_aligned_touch_input_ &&
+            IsAsyncTouchMove(shared_state_.events_.front())) {
+          if (shared_state_.events_.size() == 1 &&
+              frame_time < shared_state_.last_async_touch_move_timestamp_ +
+                               kAsyncTouchMoveInterval) {
+            break;
+          }
+          shared_state_.last_async_touch_move_timestamp_ = frame_time;
         }
-        shared_state_.last_async_touch_move_timestamp_ = frame_time;
       }
       events_to_process.emplace_back(shared_state_.events_.Pop());
     }
   }
 
   while(!events_to_process.empty()) {
     in_flight_event_ = std::move(events_to_process.front());
     events_to_process.pop_front();
     DispatchInFlightEvent();
   }
   PossiblyScheduleMainFrame();
 }
 
 void MainThreadEventQueue::SendEventNotificationToMainThread() {

[mustaq, 2017/03/24 15:31:18]

Since there is really no notification here, may be call it
|DispatchEventsToMainThread|?

[dtapuska, 2017/03/24 20:16:33]

That would mean that we are somehow transferring them. But I've renamed it to
PostTaskToMainThread()

   main_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&MainThreadEventQueue::DispatchSingleEvent, this));
+      FROM_HERE, base::Bind(&MainThreadEventQueue::DispatchEvents, this));
 }
 
-void MainThreadEventQueue::QueueEvent(
-    std::unique_ptr<EventWithDispatchType> event) {
-  bool is_raf_aligned = IsRafAlignedEvent(event->event());
-  size_t send_notification_count = 0;
+void MainThreadEventQueue::QueueEvent(std::unique_ptr<QueuedItem> event) {
+  bool is_raf_aligned = IsRafAlignedEvent(event);
   bool needs_main_frame = false;
+  bool needs_post_task = false;
   {

[mustaq, 2017/03/24 15:31:18]

I will take a look at this block again.

[dtapuska, 2017/03/24 20:16:31]

Acknowledged.

     base::AutoLock lock(shared_state_lock_);
     size_t size_before = shared_state_.events_.size();
 
     // Stash if the tail of the queue was rAF aligned.
     bool was_raf_aligned = false;
     if (size_before > 0) {
       was_raf_aligned =
-          IsRafAlignedEvent(shared_state_.events_.at(size_before - 1)->event());
+          IsRafAlignedEvent(shared_state_.events_.at(size_before - 1));
     }
     shared_state_.events_.Queue(std::move(event));
     size_t size_after = shared_state_.events_.size();
 
     if (size_before != size_after) {
-      if (IsRafAlignedInputDisabled()) {
-        send_notification_count = 1;
-      } else if (!is_raf_aligned) {
-        send_notification_count = 1;
-        // If we had just enqueued a non-rAF input event we will send a series
-        // of normal post messages to ensure they are all handled right away.
-        for (size_t pos = size_after - 1; pos >= 1; --pos) {
-          if (IsRafAlignedEvent(shared_state_.events_.at(pos - 1)->event()))
-            send_notification_count++;
-          else
-            break;
-        }
+      if (IsRafAlignedInputDisabled() || !is_raf_aligned) {
+        needs_post_task = !shared_state_.sent_post_task_;
+        shared_state_.sent_post_task_ = true;
       } else {
         needs_main_frame = !shared_state_.sent_main_frame_request_;
         shared_state_.sent_main_frame_request_ = true;
       }
     } else if (size_before > 0) {

[mustaq, 2017/03/24 15:31:18]

I think we never expect size_before == 0 here right? Please add a dcheck then.

[dtapuska, 2017/03/24 20:16:31]

Well the elseif condition is size_before > 0 so why would we add a dcheck?

[mustaq, 2017/03/27 15:54:30]

Let me clarify: the |else| should be unconditional, and the condition should
move to a dcheck inside |else {...}| instead.

- shared_state_.events_.Queue() => size_after > 0.
- |if|-|else| block => size_before == _after.
- Therefore, size_before > 0 here.

       // The event was coalesced. The queue size didn't change but
       // the rAF alignment of the event may have and we need to schedule
       // a notification.
       bool is_coalesced_raf_aligned =
-          IsRafAlignedEvent(shared_state_.events_.at(size_before - 1)->event());
-      if (was_raf_aligned != is_coalesced_raf_aligned)
-        send_notification_count = 1;
+          IsRafAlignedEvent(shared_state_.events_.at(size_before - 1));
+      if (was_raf_aligned != is_coalesced_raf_aligned) {
+        needs_post_task = !shared_state_.sent_post_task_;
+        shared_state_.sent_post_task_ = true;
+      }
     }
   }
 
-  for (size_t i = 0; i < send_notification_count; ++i)
+  if (needs_post_task)
     SendEventNotificationToMainThread();
   if (needs_main_frame)
     client_->NeedsMainFrame(routing_id_);
 }
 
-bool MainThreadEventQueue::IsRafAlignedInputDisabled() {
+bool MainThreadEventQueue::IsRafAlignedInputDisabled() const {
   return !handle_raf_aligned_mouse_input_ && !handle_raf_aligned_touch_input_;
 }
 
 bool MainThreadEventQueue::IsRafAlignedEvent(
-    const blink::WebInputEvent& event) {
-  switch (event.type()) {
+    const std::unique_ptr<QueuedItem>& item) const {
+  if (!item->IsEvent())
+    return false;
+  const EventWithDispatchType* event =
+      static_cast<const EventWithDispatchType*>(item.get());
+  switch (event->event().type()) {
     case blink::WebInputEvent::MouseMove:
     case blink::WebInputEvent::MouseWheel:
       return handle_raf_aligned_mouse_input_;
     case blink::WebInputEvent::TouchMove:
       return handle_raf_aligned_touch_input_;
     default:
       return false;
   }
 }
 
 }  // namespace content