input: Dispatch synthesized events at regular intervals.

content/browser/renderer_host/input/synthetic_gesture_controller.cc

 // Copyright 2013 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/browser/renderer_host/input/synthetic_gesture_controller.h"
 
 #include <utility>
 
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 22 matching lines @@
 
   bool was_empty = pending_gesture_queue_.IsEmpty();
 
   pending_gesture_queue_.Push(std::move(synthetic_gesture),
                               completion_callback);
 
   if (was_empty)
     StartGesture(*pending_gesture_queue_.FrontGesture());
 }
 
-void SyntheticGestureController::RequestBeginFrame() {
+void SyntheticGestureController::RequestBeginFrameIfNecessary() {
+  if (dispatch_timer_.IsRunning())
+    return;
   delegate_->RequestBeginFrameForSynthesizedInput(
       base::BindOnce(&SyntheticGestureController::OnBeginFrame,
                      weak_ptr_factory_.GetWeakPtr()));
 }
 
 void SyntheticGestureController::OnBeginFrame() {
-  // TODO(sad): Instead of dispatching the events immediately, dispatch after an
-  // offset.
-  DispatchNextEvent();
+  constexpr base::TimeDelta kSynthesizedDispatchDelay =

[dtapuska, 2017/05/19 18:32:27]

I think we need an explanation around why 2 is a *good* time. (Basically
identifying we felt 2 was good there is not a lot of experimentation that went
into it).

[sadrul, 2017/05/19 18:46:03]

Added a note. PTAL.

+      base::TimeDelta::FromMilliseconds(2);
+  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
+      FROM_HERE,
+      base::BindOnce(&SyntheticGestureController::StartTimer,
+                     weak_ptr_factory_.GetWeakPtr()),
+      kSynthesizedDispatchDelay);
+}
+
+void SyntheticGestureController::StartTimer() {
+  // TODO(sad): Change the interval to allow sending multiple events per begin
+  // frame.
+  dispatch_timer_.Start(
+      FROM_HERE, base::TimeDelta::FromMicroseconds(16666),
+      base::BindRepeating(
+          [](base::WeakPtr<SyntheticGestureController> weak_ptr) {
+            if (weak_ptr)
+              weak_ptr->DispatchNextEvent(base::TimeTicks::Now());
+          },
+          weak_ptr_factory_.GetWeakPtr()));
 }
 
 bool SyntheticGestureController::DispatchNextEvent(base::TimeTicks timestamp) {
   TRACE_EVENT0("input", "SyntheticGestureController::Flush");
   if (pending_gesture_queue_.IsEmpty())
     return false;
 
   if (!pending_gesture_queue_.is_current_gesture_complete()) {
     SyntheticGesture::Result result =
         pending_gesture_queue_.FrontGesture()->ForwardInputEvents(
             timestamp, gesture_target_.get());
 
     if (result == SyntheticGesture::GESTURE_RUNNING) {
-      RequestBeginFrame();
+      RequestBeginFrameIfNecessary();

[dtapuska, 2017/05/19 18:32:27]

Could this be a DCHECK(dispatch_timer_.IsRunning()) instead?

[sadrul, 2017/05/19 18:46:03]

I had a DCHECK() at the beginning of the function here. But the unit-tests
tripped on it (because they directly dispatch the events [1]). I can add the
DCHECK() back and update the test instead though.

[1]
https://cs.chromium.org/chromium/src/content/browser/renderer_host/input/synt...

[sadrul, 2017/05/19 19:02:49]

I have gone ahead and added the DCHECK() back, and updated the test to have a
ScopedTaskEnvironment, and start/stop the timer in the test.

       return true;
     }
     pending_gesture_queue_.mark_current_gesture_complete(result);
   }
 
   if (!delegate_->HasGestureStopped()) {
-    RequestBeginFrame();
+    RequestBeginFrameIfNecessary();

[dtapuska, 2017/05/19 18:32:27]

same here.

     return true;
   }
 
   StopGesture(*pending_gesture_queue_.FrontGesture(),
               pending_gesture_queue_.FrontCallback(),
               pending_gesture_queue_.current_gesture_result());
   pending_gesture_queue_.Pop();
-  if (pending_gesture_queue_.IsEmpty())
+  if (pending_gesture_queue_.IsEmpty()) {
+    dispatch_timer_.Stop();
     return false;
+  }
   StartGesture(*pending_gesture_queue_.FrontGesture());
   return true;
 }
 
 void SyntheticGestureController::StartGesture(const SyntheticGesture& gesture) {
   TRACE_EVENT_ASYNC_BEGIN0("input,benchmark",
                            "SyntheticGestureController::running",
                            &gesture);
-  RequestBeginFrame();
+  RequestBeginFrameIfNecessary();
 }
 
 void SyntheticGestureController::StopGesture(
     const SyntheticGesture& gesture,
     const OnGestureCompleteCallback& completion_callback,
     SyntheticGesture::Result result) {
   DCHECK_NE(result, SyntheticGesture::GESTURE_RUNNING);
   TRACE_EVENT_ASYNC_END0("input,benchmark",
                          "SyntheticGestureController::running",
                          &gesture);
 
   completion_callback.Run(result);
 }
 
 SyntheticGestureController::GestureAndCallbackQueue::GestureAndCallbackQueue() {
 }
 
 SyntheticGestureController::GestureAndCallbackQueue::
     ~GestureAndCallbackQueue() {
 }
 
 }  // namespace content