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

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

 // Copyright 2014 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 THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_
 
 #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"
 #include "platform/scheduler/child/idle_helper.h"
 #include "platform/scheduler/child/scheduler_helper.h"
 #include "platform/scheduler/renderer/deadline_task_runner.h"
 #include "platform/scheduler/renderer/idle_time_estimator.h"
 #include "platform/scheduler/renderer/render_widget_signals.h"
 #include "platform/scheduler/renderer/task_cost_estimator.h"
 #include "platform/scheduler/renderer/user_model.h"
@@ skipping 94 matching lines @@
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer) override;
   void RemoveTaskObserver(
       base::MessageLoop::TaskObserver* task_observer) override;
   void Shutdown() override;
   void SuspendTimerQueue() override;
   void ResumeTimerQueue() override;
   void SetTimerQueueSuspensionWhenBackgroundedEnabled(bool enabled) override;
   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;
   void SetHasVisibleRenderWidgetWithTouchHandler(
       bool has_visible_render_widget_with_touch_handler) override;
 
   // SchedulerHelper::Observer implementation:
   void OnUnregisterTaskQueue(const scoped_refptr<TaskQueue>& queue) override;
   void OnTriedToExecuteBlockedTask(const TaskQueue& queue,
                                    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;
 
   // Returns a task runner where tasks run at the highest possible priority.
   scoped_refptr<TaskQueue> ControlTaskRunner();
 
   void RegisterTimeDomain(TimeDomain* time_domain);
   void UnregisterTimeDomain(TimeDomain* time_domain);
 
@@ skipping 221 matching lines @@
   scoped_refptr<TaskQueue> default_timer_task_runner_;
 
   // Note |virtual_time_domain_| is lazily created.
   std::unique_ptr<AutoAdvancingVirtualTimeDomain> virtual_time_domain_;
 
   base::Closure update_policy_closure_;
   DeadlineTaskRunner delayed_update_policy_runner_;
   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.
 
   struct MainThreadOnly {
     MainThreadOnly(RendererSchedulerImpl* renderer_scheduler_impl,
                    const scoped_refptr<TaskQueue>& compositor_task_runner,
                    base::TickClock* time_source,
                    base::TimeTicks now);
     ~MainThreadOnly();
 
     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;
     UseCase current_use_case;
     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;
     int timer_queue_suspend_count;  // TIMER_TASK_QUEUE suspended if non-zero.
     int navigation_task_expected_count;
     ExpensiveTaskPolicy expensive_task_policy;
     bool renderer_hidden;
     bool renderer_backgrounded;
     bool renderer_suspended;
     bool timer_queue_suspension_when_backgrounded_enabled;
     bool timer_queue_suspended_when_backgrounded;
     bool was_shutdown;
     bool loading_tasks_seem_expensive;
     bool timer_tasks_seem_expensive;
     bool touchstart_expected_soon;
     bool have_seen_a_begin_main_frame;
     bool have_reported_blocking_intervention_in_current_policy;
     bool have_reported_blocking_intervention_since_navigation;
     bool has_visible_render_widget_with_touch_handler;
     bool begin_frame_not_expected_soon;
     bool in_idle_period_for_testing;
     bool use_virtual_time;
     bool is_audio_playing;
     std::set<WebViewSchedulerImpl*> web_view_schedulers;  // Not owned.
     RAILModeObserver* rail_mode_observer;                 // Not owned.
   };
 
   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;
     base::TimeTicks rails_loading_priority_deadline;
     base::TimeTicks fling_compositor_escalation_deadline;
     UserModel user_model;
     bool awaiting_touch_start_response;
     bool in_idle_period;
     bool begin_main_frame_on_critical_path;
     bool last_gesture_was_compositor_driven;
     bool default_gesture_prevented;
     bool have_seen_touchstart;
   };
 
   struct CompositorThreadOnly {
     CompositorThreadOnly();
     ~CompositorThreadOnly();
 
     WebInputEvent::Type last_input_type;
+    bool main_thread_seems_unresponsive;
     std::unique_ptr<base::ThreadChecker> compositor_thread_checker;
 
     void CheckOnValidThread() {
 #if DCHECK_IS_ON()
       // We don't actually care which thread this called from, just so long as
       // its consistent.
       if (!compositor_thread_checker)
         compositor_thread_checker.reset(new base::ThreadChecker());
       DCHECK(compositor_thread_checker->CalledOnValidThread());
 #endif
@@ skipping 24 matching lines @@
   }
 
   // Don't access compositor_thread_only_, instead use CompositorThreadOnly().
   CompositorThreadOnly compositor_thread_only_;
   CompositorThreadOnly& CompositorThreadOnly() {
     compositor_thread_only_.CheckOnValidThread();
     return compositor_thread_only_;
   }
 
   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);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_