Send idle notifications to V8 after commit

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 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/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 20 matching lines @@
 #include "content/common/content_switches_internal.h"
 #include "content/common/gpu/client/context_provider_command_buffer.h"
 #include "content/public/common/content_switches.h"
 #include "content/renderer/compositor_bindings/web_layer_impl.h"
 #include "content/renderer/input/input_handler_manager.h"
 #include "content/renderer/render_thread_impl.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "third_party/WebKit/public/platform/WebCompositeAndReadbackAsyncCallback.h"
 #include "third_party/WebKit/public/platform/WebSelectionBound.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
+#include "third_party/WebKit/public/web/WebKit.h"
 #include "third_party/WebKit/public/web/WebWidget.h"
 #include "ui/gfx/frame_time.h"
 #include "ui/gl/gl_switches.h"
 #include "ui/native_theme/native_theme_switches.h"
 
 #if defined(OS_ANDROID)
 #include "content/renderer/android/synchronous_compositor_factory.h"
 #include "ui/gfx/android/device_display_info.h"
 #endif
 
@@ skipping 699 matching lines @@
 void RenderWidgetCompositor::WillBeginMainFrame(int frame_id) {
   widget_->InstrumentWillBeginFrame(frame_id);
   widget_->willBeginCompositorFrame();
 }
 
 void RenderWidgetCompositor::DidBeginMainFrame() {
   widget_->InstrumentDidBeginFrame();
 }
 
 void RenderWidgetCompositor::BeginMainFrame(const cc::BeginFrameArgs& args) {
+  begin_main_frame_args_ = args;
   double frame_time = (args.frame_time - base::TimeTicks()).InSecondsF();
   WebBeginFrameArgs web_begin_frame_args = WebBeginFrameArgs(frame_time);
   widget_->webwidget()->beginFrame(web_begin_frame_args);
 }
 
 void RenderWidgetCompositor::Layout() {
   widget_->webwidget()->layout();
 }
 
 void RenderWidgetCompositor::ApplyScrollAndScale(
     const gfx::Vector2d& scroll_delta,
     float page_scale) {
   widget_->webwidget()->applyScrollAndScale(scroll_delta, page_scale);
 }
 
 scoped_ptr<cc::OutputSurface> RenderWidgetCompositor::CreateOutputSurface(
     bool fallback) {
   return widget_->CreateOutputSurface(fallback);
 }
 
 void RenderWidgetCompositor::DidInitializeOutputSurface() {
 }
 
 void RenderWidgetCompositor::WillCommit() {
   widget_->InstrumentWillComposite();
 }
 
 void RenderWidgetCompositor::DidCommit() {
+  CommandLine* cmd = CommandLine::ForCurrentProcess();
+  if (cmd->HasSwitch(switches::kSendV8IdleNotificationAfterCommit)) {

[jamesr, 2014/08/20 19:38:41]

grab this value once and stash it in a bool, it can't change over time. 
HasSwitch() is a lowercase conversion (on windows) and an std::map<> lookup, so
not terribly slow, but no need to bother doing this over and over when it'll
always give us the same answer

[ernstm, 2014/08/21 18:22:00]

Done.

+    int idle_time_in_ms =
+        std::max(0L, (begin_main_frame_args_.frame_time +
+                      begin_main_frame_args_.interval -
+                      base::TimeTicks::HighResNow()).InMilliseconds());

[jamesr, 2014/08/20 19:38:41]

i was under the impression BeginFrameArgs was built on top of
gfx::FrameTime::Now(), not base::TimeTicks::HighResNow().  Can you check this
please?

[brianderson, 2014/08/20 20:07:47]

James is correct. Using HighResNow() here directly will break on Windows. You
should use gfx::FrameTime::Now() instead.

[ernstm, 2014/08/21 18:22:00]

Done.

+    if (idle_time_in_ms)
+      blink::mainThreadIsolate()->IdleNotification(idle_time_in_ms);

[jamesr, 2014/08/20 19:38:41]

why the main thread isolate in particular? what about other heaps?

[ernstm, 2014/08/21 18:22:00]

The goal is to reduce jank caused by GC on the main thread before the commit.
Web workers already run in separate threads, so shouldn't cause problems.

+  }
+
   widget_->DidCommitCompositorFrame();
   widget_->didBecomeReadyForAdditionalInput();
 }
 
 void RenderWidgetCompositor::DidCommitAndDrawFrame() {
   widget_->didCommitAndDrawCompositorFrame();
 }
 
 void RenderWidgetCompositor::DidCompleteSwapBuffers() {
   widget_->didCompleteSwapBuffers();
@@ skipping 18 matching lines @@
   widget_->OnSwapBuffersAborted();
 }
 
 void RenderWidgetCompositor::RateLimitSharedMainThreadContext() {
   cc::ContextProvider* provider =
       RenderThreadImpl::current()->SharedMainThreadContextProvider().get();
   provider->ContextGL()->RateLimitOffscreenContextCHROMIUM();
 }
 
 }  // namespace content