[POC; Not for Review] 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 "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 "ipc/message_filter.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 {
  public:
   EventWithDispatchType(const BaseType& e,
                         const ui::LatencyInfo& l,
@@ skipping 12 matching lines @@
   }
 };
 
 using PendingMouseWheelEvent =
     EventWithDispatchType<MouseWheelEventWithLatencyInfo,
                           blink::WebMouseWheelEvent>;
 
 using PendingTouchEvent =
     EventWithDispatchType<TouchEventWithLatencyInfo, blink::WebTouchEvent>;
 
+using PendingMouseEvent =
+    EventWithDispatchType<MouseEventWithLatencyInfo, blink::WebMouseEvent>;
+
 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;
 };
 
 // MainThreadEventQueue implements a series of queues (one touch
 // and one mouse wheel) for events that need to be queued between
 // 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.

[tdresser, 2016/05/30 14:05:32]

Don't forget to change this comment.

 //
 // Below some example flows are how the code behaves.
 // Legend: B=Browser, C=Compositor, M=Main Thread, NB=Non-blocking
 //         BL=Blocking, PT=Post Task, ACK=Acknowledgement
 //
 // Normal blocking event sent to main thread.
 //   B        C        M
 //   ---(BL)-->
 //            ---(PT)-->
 //   <-------(ACK)------
 //
 // Non-blocking event sent to main thread.
 //   B        C        M
 //   ---(NB)-->
 //            ---(PT)-->
 //            <--(PT)---
 //
 // 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 {
  public:
-  MainThreadEventQueue(int routing_id, MainThreadEventQueueClient* client);
+  MainThreadEventQueue(
+      int routing_id,
+      MainThreadEventQueueClient* client,
+      const base::Callback<void(const IPC::Message&)>& main_listener,
+      const scoped_refptr<base::SingleThreadTaskRunner>& main_task_runner);
   ~MainThreadEventQueue();
 
   // 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);
 
   void set_is_flinging(bool is_flinging) { is_flinging_ = is_flinging; }
 
  private:
+  void QueueWheelEvent(const PendingMouseWheelEvent& event);
+  void QueueTouchEvent(const PendingTouchEvent& event);
+  void QueueMouseEvent(const PendingMouseEvent& event);
+  void SendWheelEventNotificationToMainThread();
+  void SendTouchEventNotificationToMainThread();
+  void SendMouseEventNotificationToMainThread();
+  void PopTouchEventOnMainThread();
+  void PopWheelEventOnMainThread();
+  void PopMouseEventOnMainThread();
+  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<PendingMouseEvent> mouse_events_;
   bool is_flinging_;
+  base::Lock event_queue_mutex_;
+  scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
+  base::Callback<void(const IPC::Message&)> main_listener_;

[tdresser, 2016/05/30 14:05:32]

Eventually we'll want a couple ThreadChecker's in here.

https://code.google.com/p/chromium/codesearch#chromium/src/base/threading/thr...

[dtapuska, 2016/06/01 18:22:54]

Acknowledged.

 
   DISALLOW_COPY_AND_ASSIGN(MainThreadEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_INPUT_MAIN_THREAD_EVENT_QUEUE_H_