Don't use PostTask queueing between compositor and main thread.

content/renderer/input/main_thread_event_queue.h

 // 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.
 
 #ifndef CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_H_
 #define CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_H_
 
 #include <deque>
+#include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "content/common/input/event_with_latency_info.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "content/common/input/input_event_dispatch_type.h"
 #include "content/common/input/web_input_event_queue.h"
 #include "content/common/input/web_input_event_traits.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/events/latency_info.h"
 
 namespace content {
 
-template <typename BaseClass, typename BaseType>
-class EventWithDispatchType : public BaseClass {
+class EventWithDispatchType : public ScopedWebInputEventWithLatencyInfo {
  public:
-  EventWithDispatchType(const BaseType& e,
-                        const ui::LatencyInfo& l,
-                        InputEventDispatchType t)
-      : BaseClass(e, l), type(t) {}
+  EventWithDispatchType(const blink::WebInputEvent& event,
+                        const ui::LatencyInfo& latency,
+                        InputEventDispatchType dispatch_type);
+  ~EventWithDispatchType();
+  bool CanCoalesceWith(const EventWithDispatchType& other) const
+      WARN_UNUSED_RESULT;
+  void CoalesceWith(const EventWithDispatchType& other);
 
-  InputEventDispatchType type;
-  std::deque<uint32_t> eventsToAck;
+  const std::deque<uint32_t>& eventsToAck() const { return eventsToAck_; }
+  InputEventDispatchType dispatchType() const { return dispatch_type_; }
 
-  bool CanCoalesceWith(const EventWithDispatchType& other) const
-      WARN_UNUSED_RESULT {
-    return other.type == type && BaseClass::CanCoalesceWith(other);
-  }
-
-  void CoalesceWith(const EventWithDispatchType& other) {
-    // If we are blocking and are coalescing touch, make sure to keep
-    // the touch ids that need to be acked.
-    if (type == DISPATCH_TYPE_BLOCKING_NOTIFY_MAIN) {
-      // We should only have blocking touch events that need coalescing.
-      DCHECK(blink::WebInputEvent::isTouchEventType(other.event.type));
-      eventsToAck.push_back(
-          WebInputEventTraits::GetUniqueTouchEventId(other.event));
-    }
-    BaseClass::CoalesceWith(other);
-  }
+ private:
+  InputEventDispatchType dispatch_type_;
+  std::deque<uint32_t> eventsToAck_;

[tdresser, 2016/07/20 20:52:27]

Make it clear this is touch only.

[dtapuska, 2016/07/27 05:29:00]

Acknowledged.

 };
 
-using PendingMouseWheelEvent =
-    EventWithDispatchType<MouseWheelEventWithLatencyInfo,
-                          blink::WebMouseWheelEvent>;
-
-using PendingTouchEvent =
-    EventWithDispatchType<TouchEventWithLatencyInfo, blink::WebTouchEvent>;
-
 class CONTENT_EXPORT MainThreadEventQueueClient {
  public:
-  // Send an |event| that was previously queued (possibly
+  // Handle an |event| that was previously queued (possibly
   // coalesced with another event) to the |routing_id|'s
   // channel. Implementors must implement this callback.
-  virtual void SendEventToMainThread(int routing_id,
-                                     const blink::WebInputEvent* event,
-                                     const ui::LatencyInfo& latency,
-                                     InputEventDispatchType dispatch_type) = 0;
+  virtual void HandleEventOnMainThread(
+      int routing_id,
+      const blink::WebInputEvent* event,
+      const ui::LatencyInfo& latency,
+      InputEventDispatchType dispatch_type) = 0;
 
   virtual void SendInputEventAck(int routing_id,
                                  blink::WebInputEvent::Type type,
                                  InputEventAckState ack_result,
                                  uint32_t touch_event_id) = 0;
 };
 
 // MainThreadEventQueue implements a series of queues (one touch
 // and one mouse wheel) for events that need to be queued between

[tdresser, 2016/07/20 20:52:27]

Update comment.

 // the compositor and main threads. When an event is sent
 // from the compositor to main it can either be sent directly if no
 // outstanding events of that type are in flight; or it needs to
 // wait in a queue until the main thread has finished processing
 // the in-flight event. This class tracks the state and queues
 // for the event types. Methods on this class should only be called
 // from the compositor thread.
 //
 // Below some example flows are how the code behaves.
 // Legend: B=Browser, C=Compositor, M=Main Thread, NB=Non-blocking
@@ skipping 14 matching lines @@
 // Non-blocking followed by blocking event sent to main thread.
 //   B        C        M
 //   ---(NB)-->
 //            ---(PT)-->
 //   ---(BL)-->
 //            <--(PT)---     // Notify from NB event.
 //            ---(PT)-->     // Release blocking event.
 //            <--(PT)---     // Notify from BL event.
 //   <-------(ACK)------
 //
-class CONTENT_EXPORT MainThreadEventQueue {
+class CONTENT_EXPORT MainThreadEventQueue
+    : public base::RefCountedThreadSafe<MainThreadEventQueue> {
  public:
-  MainThreadEventQueue(int routing_id, MainThreadEventQueueClient* client);
-  ~MainThreadEventQueue();
+  MainThreadEventQueue(
+      int routing_id,
+      MainThreadEventQueueClient* client,
+      const scoped_refptr<base::SingleThreadTaskRunner>& main_task_runner);
 
   // Called once the compositor has handled |event| and indicated that it is
   // a non-blocking event to be queued to the main thread.
   bool HandleEvent(const blink::WebInputEvent* event,
                    const ui::LatencyInfo& latency,
                    InputEventDispatchType dispatch_type,
                    InputEventAckState ack_result);
 
   // Call once the main thread has handled an outstanding |type| event
   // in flight.
   void EventHandled(blink::WebInputEvent::Type type,
                     InputEventAckState ack_result);
 
   void set_is_flinging(bool is_flinging) { is_flinging_ = is_flinging; }
 
  private:
+  friend class base::RefCountedThreadSafe<MainThreadEventQueue>;
+  ~MainThreadEventQueue();
+  void QueueEvent(std::unique_ptr<EventWithDispatchType>&& event);
+  void SendEventNotificationToMainThread();
+  void PopEventOnMainThread();
+  void SendEventToMainThread(const blink::WebInputEvent* event,
+                             const ui::LatencyInfo& latency,
+                             InputEventDispatchType original_dispatch_type);
+
   friend class MainThreadEventQueueTest;
   int routing_id_;
   MainThreadEventQueueClient* client_;
-  WebInputEventQueue<PendingMouseWheelEvent> wheel_events_;
-  WebInputEventQueue<PendingTouchEvent> touch_events_;
+  WebInputEventQueue<EventWithDispatchType> events_;
+  std::unique_ptr<EventWithDispatchType> in_flight_event_;
   bool is_flinging_;

[tdresser, 2016/07/20 20:52:27]

Do we still need is_flinging?

[dtapuska, 2016/07/27 05:29:00]

yes sorry that was missing code.

-
-  // TODO(dtapuska): These can be removed when the queues are dequeued
-  // on the main thread. See crbug.com/624021
-  std::unique_ptr<PendingMouseWheelEvent> in_flight_wheel_event_;
-  std::unique_ptr<PendingTouchEvent> in_flight_touch_event_;
+  base::Lock event_queue_mutex_;
+  scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(MainThreadEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_H_