Force events to be non blocking if main thread is unresponsive.

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h

Index: third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h
index bc0c3d61673941d281a437980f1da94c676af044..f43c1beacbd0364e6b3d90184e2907a29beb872e 100644
--- a/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl.h
@@ -8,6 +8,7 @@
 #include "base/atomicops.h"
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
+#include "device/base/synchronization/shared_memory_seqlock_buffer.h"
 #include "platform/scheduler/base/pollable_thread_safe_flag.h"
 #include "platform/scheduler/base/queueing_time_estimator.h"
 #include "platform/scheduler/base/thread_load_tracker.h"
@@ -122,6 +123,7 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
   void SetTopLevelBlameContext(
       base::trace_event::BlameContext* blame_context) override;
   void SetRAILModeObserver(RAILModeObserver* observer) override;
+  bool MainThreadSeemsUnresponsive() override;
 
   // RenderWidgetSignals::Observer implementation:
   void SetAllRenderWidgetsHidden(bool hidden) override;
@@ -134,9 +136,10 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
                                    const base::PendingTask& task) override;
 
   // TaskTimeObserver implementation:
-  void ReportTaskTime(TaskQueue* task_queue,
-                      double start_time,
-                      double end_time) override;
+  void ReportTaskStartTime(double start_time) override;
+  void ReportTaskEndTime(TaskQueue* task_queue,
+                         double start_time,
+                         double end_time) override;
 
   // QueueingTimeEstimator::Client implementation:
   void OnQueueingTimeForWindowEstimated(base::TimeDelta queueing_time) override;
@@ -378,6 +381,11 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
   CancelableClosureHolder end_renderer_hidden_idle_period_closure_;
   CancelableClosureHolder suspend_timers_when_backgrounded_closure_;
 
+  using SeqLockQueueingTimeEstimator =
+      device::SharedMemorySeqLockBuffer<QueueingTimeEstimator>;
+
+  SeqLockQueueingTimeEstimator seqlock_queueing_time_estimator_;

[Sami, 2016/11/14 21:16:45]

Please add a short note here saying that this only protects access to the data()
method of the estimator. I was trying to think of a way to have this be a ::Data
instead, but I couldn't think of a straightforward way (unless we make the class
that is signalling the client be able to use external storage for Data somehow).

[tdresser, 2016/12/15 13:17:00]

Why do you say it only protects access to the data() method of the estimator?
The SharedMemorySeqlockBuffer's data attribute is protected, which is the whole
QueueingTimeEstimatorObject.

[Sami, 2016/12/15 17:54:37]

I'm a little fuzzy on what I was going for here, but it may have been the fact
that this isn't an actual lock that lets two different parties mutate the object
concurrently. I now think it should be obvious enough since we have "seqlock" in
the name.

[tdresser, 2016/12/15 19:16:09]

Done.

+
   // We have decided to improve thread safety at the cost of some boilerplate
   // (the accessors) for the following data members.
 
@@ -390,7 +398,6 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
 
     TaskCostEstimator loading_task_cost_estimator;
     TaskCostEstimator timer_task_cost_estimator;
-    QueueingTimeEstimator queueing_time_estimator;
     IdleTimeEstimator idle_time_estimator;
     ThreadLoadTracker background_main_thread_load_tracker;
     ThreadLoadTracker foreground_main_thread_load_tracker;
@@ -398,6 +405,7 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
     Policy current_policy;
     base::TimeTicks current_policy_expiration_time;
     base::TimeTicks estimated_next_frame_begin;
+    base::TimeTicks current_task_start_time;
     base::TimeDelta compositor_frame_interval;
     base::TimeDelta longest_jank_free_task_duration;
     base::Optional<base::TimeTicks> last_audio_state_change;
@@ -426,7 +434,7 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
   };
 
   struct AnyThread {
-    AnyThread();
+    AnyThread(RendererSchedulerImpl* renderer_scheduler_impl);

[alex clarke (OOO till 29th), 2016/11/14 17:00:17]

explicit 

[tdresser, 2016/12/15 13:17:00]

Done.

     ~AnyThread();
 
     base::TimeTicks last_idle_period_end_time;
@@ -446,6 +454,7 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
     ~CompositorThreadOnly();
 
     WebInputEvent::Type last_input_type;
+    bool main_thread_seems_unresponsive;
     std::unique_ptr<base::ThreadChecker> compositor_thread_checker;
 
     void CheckOnValidThread() {
@@ -490,6 +499,10 @@ class BLINK_PLATFORM_EXPORT RendererSchedulerImpl
   }
 
   PollableThreadSafeFlag policy_may_need_update_;
+  // The maximum expected queueing time before the main thread is considered
+  // unresponsive.
+  base::TimeDelta main_thread_responsiveness_threshold_;

[Sami, 2016/11/14 21:16:45]

Do you still need this given the constant is a TimeDelta now too? (and the test
is using the same default value of 200ms)

[tdresser, 2016/12/15 13:17:00]

There's nothing worse than trying to land a change to a constant, and realizing
it makes all your tests fail. I'd prefer we keep the test value independent, so
that when we decide to tweak this, we don't need to update a bunch of tests.

+
   base::WeakPtrFactory<RendererSchedulerImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererSchedulerImpl);