[scheduler] Make TaskQueueImpl own next_scheduled_wake_up information.

Refactor the scheme where TaskQueueImpl notifies TimeDomain about a
delayed wake up and TimeDomain notifies TaskQueueImpl about next wake-up for it.

Make TaskQueueImpl be the ground truth for delayed wake-ups for the
particular queue and task TimeDomain with aggregating wake-ups across
different queues.

R=alexclarke@chromium.org,skyostil@chromium.org

Change-Id: I7d56d35e9c7b5b2bb1240a6a659d0d9a1f00c473
Reviewed-on: https://chromium-review.googlesource.com/955847Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543730}

third_party/WebKit/Source/platform/scheduler/base/lazy_now.cc

@@ -9,9 +9,9 @@
 namespace blink {
 namespace scheduler {
 base::TimeTicks LazyNow::Now() {
-  if (now_.is_null())
+  if (!now_)
     now_ = tick_clock_->NowTicks();
-  return now_;
+  return now_.value();
 }
 
 }  // namespace scheduler

third_party/WebKit/Source/platform/scheduler/base/lazy_now.h

@@ -5,6 +5,7 @@
 #ifndef THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_LAZY_NOW_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_LAZY_NOW_H_
 
+#include "base/optional.h"
 #include "base/time/time.h"
 #include "platform/PlatformExport.h"
 
@@ -20,7 +21,6 @@ namespace scheduler {
 class PLATFORM_EXPORT LazyNow {
  public:
   explicit LazyNow(base::TimeTicks now) : tick_clock_(nullptr), now_(now) {
-    DCHECK(!now.is_null());
   }
 
   explicit LazyNow(base::TickClock* tick_clock) : tick_clock_(tick_clock) {}
@@ -30,7 +30,7 @@ class PLATFORM_EXPORT LazyNow {
 
  private:
   base::TickClock* tick_clock_;  // NOT OWNED
-  base::TimeTicks now_;
+  base::Optional<base::TimeTicks> now_;
 };
 
 }  // namespace scheduler

third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.cc

@@ -254,20 +254,11 @@ TaskQueueImpl::PostTaskResult TaskQueueImpl::PostDelayedTaskImpl(
 
 void TaskQueueImpl::PushOntoDelayedIncomingQueueFromMainThread(
     Task pending_task, base::TimeTicks now) {
-  DelayedWakeUp wake_up = pending_task.delayed_wake_up();
   main_thread_only().task_queue_manager->DidQueueTask(pending_task);
   main_thread_only().delayed_incoming_queue.push(std::move(pending_task));
 
-  // If |pending_task| is at the head of the queue, then make sure a wake-up
-  // is requested if the queue is enabled.  Note we still want to schedule a
-  // wake-up even if blocked by a fence, because we'd break throttling logic
-  // otherwise.
-  DelayedWakeUp new_wake_up =
-      main_thread_only().delayed_incoming_queue.top().delayed_wake_up();
-  if (wake_up.time == new_wake_up.time &&
-      wake_up.sequence_num == new_wake_up.sequence_num) {
-    ScheduleDelayedWorkInTimeDomain(now);
-  }
+  LazyNow lazy_now = main_thread_only().time_domain->CreateLazyNow();
+  UpdateDelayedWakeUp(&lazy_now);
 
   TraceQueueSize();
 }
@@ -420,16 +411,23 @@ bool TaskQueueImpl::HasTaskToRunImmediately() const {
   return !immediate_incoming_queue().empty();
 }
 
-base::Optional<base::TimeTicks> TaskQueueImpl::GetNextScheduledWakeUp() {
+base::Optional<TaskQueueImpl::DelayedWakeUp>
+TaskQueueImpl::GetNextScheduledWakeUpImpl() {
   // Note we don't scheduled a wake-up for disabled queues.
   if (main_thread_only().delayed_incoming_queue.empty() || !IsQueueEnabled())
     return base::nullopt;
 
-  return main_thread_only().delayed_incoming_queue.top().delayed_run_time;
+  return main_thread_only().delayed_incoming_queue.top().delayed_wake_up();
 }
 
-base::Optional<TaskQueueImpl::DelayedWakeUp>
-TaskQueueImpl::WakeUpForDelayedWork(LazyNow* lazy_now) {
+base::Optional<base::TimeTicks> TaskQueueImpl::GetNextScheduledWakeUp() {
+  base::Optional<DelayedWakeUp> wake_up = GetNextScheduledWakeUpImpl();
+  if (!wake_up)
+    return base::nullopt;
+  return wake_up->time;
+}
+
+void TaskQueueImpl::WakeUpForDelayedWork(LazyNow* lazy_now) {
   // Enqueue all delayed tasks that should be running now, skipping any that
   // have been canceled.
   while (!main_thread_only().delayed_incoming_queue.empty()) {
@@ -446,14 +444,18 @@ TaskQueueImpl::WakeUpForDelayedWork(LazyNow* lazy_now) {
         main_thread_only().task_queue_manager->GetNextSequenceNumber());
     main_thread_only().delayed_work_queue->Push(std::move(task));
     main_thread_only().delayed_incoming_queue.pop();
-  }
 
-  // Make sure the next wake up is scheduled.
-  if (!main_thread_only().delayed_incoming_queue.empty()) {
-    return main_thread_only().delayed_incoming_queue.top().delayed_wake_up();
+    // Normally WakeUpForDelayedWork is called inside DoWork, but it also
+    // can be called elsewhere (e.g. tests and fast-path for posting
+    // delayed tasks). Ensure that there is a DoWork posting. No-op inside
+    // existing DoWork due to DoWork deduplication.
+    if (IsQueueEnabled() || !main_thread_only().current_fence) {
+      main_thread_only().task_queue_manager->MaybeScheduleImmediateWork(
+          FROM_HERE);
+    }
   }
 
-  return base::nullopt;
+  UpdateDelayedWakeUp(lazy_now);
 }
 
 void TaskQueueImpl::TraceQueueSize() const {
@@ -599,7 +601,13 @@ void TaskQueueImpl::SetTimeDomain(TimeDomain* time_domain) {
   main_thread_only().time_domain = time_domain;
   time_domain->RegisterQueue(this);
 
-  ScheduleDelayedWorkInTimeDomain(time_domain->Now());
+  LazyNow lazy_now = time_domain->CreateLazyNow();
+  // Clear scheduled wake up to ensure that new notifications are issued
+  // correctly.
+  // TODO(altimin): Remove this when we won't have to support changing time
+  // domains.
+  main_thread_only().scheduled_wake_up = base::nullopt;
+  UpdateDelayedWakeUp(&lazy_now);
 }
 
 TimeDomain* TaskQueueImpl::GetTimeDomain() const {
@@ -836,6 +844,9 @@ void TaskQueueImpl::EnableOrDisableWithSelector(bool enable) {
   if (!main_thread_only().task_queue_manager)
     return;
 
+  LazyNow lazy_now = main_thread_only().time_domain->CreateLazyNow();
+  UpdateDelayedWakeUp(&lazy_now);
+
   if (enable) {
     if (HasPendingImmediateWork() &&
         !main_thread_only().on_next_wake_up_changed_callback.is_null()) {
@@ -844,16 +855,12 @@ void TaskQueueImpl::EnableOrDisableWithSelector(bool enable) {
           base::TimeTicks());
     }
 
-    ScheduleDelayedWorkInTimeDomain(main_thread_only().time_domain->Now());
-
-    // Note the selector calls TaskQueueManagerImpl::OnTaskQueueEnabled which
-    // posts a DoWork if needed.
+    // Note the selector calls TaskQueueManager::OnTaskQueueEnabled which posts
+    // a DoWork if needed.
     main_thread_only()
         .task_queue_manager->main_thread_only()
         .selector.EnableQueue(this);
   } else {
-    if (!main_thread_only().delayed_incoming_queue.empty())
-      main_thread_only().time_domain->CancelDelayedWork(this);
     main_thread_only()
         .task_queue_manager->main_thread_only()
         .selector.DisableQueue(this);
@@ -872,9 +879,6 @@ void TaskQueueImpl::SweepCanceledDelayedTasks(base::TimeTicks now) {
   if (main_thread_only().delayed_incoming_queue.empty())
     return;
 
-  base::TimeTicks first_task_runtime =
-      main_thread_only().delayed_incoming_queue.top().delayed_run_time;
-
   // Remove canceled tasks.
   std::priority_queue<Task> remaining_tasks;
   while (!main_thread_only().delayed_incoming_queue.empty()) {
@@ -887,13 +891,8 @@ void TaskQueueImpl::SweepCanceledDelayedTasks(base::TimeTicks now) {
 
   main_thread_only().delayed_incoming_queue = std::move(remaining_tasks);
 
-  // Re-schedule delayed call to WakeUpForDelayedWork if needed.
-  if (main_thread_only().delayed_incoming_queue.empty()) {
-    main_thread_only().time_domain->CancelDelayedWork(this);
-  } else if (first_task_runtime !=
-             main_thread_only().delayed_incoming_queue.top().delayed_run_time) {
-    ScheduleDelayedWorkInTimeDomain(main_thread_only().time_domain->Now());
-  }
+  LazyNow lazy_now(now);
+  UpdateDelayedWakeUp(&lazy_now);
 }
 
 void TaskQueueImpl::PushImmediateIncomingTaskForTest(
@@ -933,31 +932,31 @@ void TaskQueueImpl::SetOnNextWakeUpChangedCallback(
   main_thread_only().on_next_wake_up_changed_callback = callback;
 }
 
-void TaskQueueImpl::ScheduleDelayedWorkInTimeDomain(base::TimeTicks now) {
-  if (!IsQueueEnabled())
-    return;
-  if (main_thread_only().delayed_incoming_queue.empty())
-    return;
-
-  main_thread_only().time_domain->ScheduleDelayedWork(
-      this, main_thread_only().delayed_incoming_queue.top().delayed_wake_up(),
-      now);
+void TaskQueueImpl::UpdateDelayedWakeUp(LazyNow* lazy_now) {
+  return UpdateDelayedWakeUpImpl(lazy_now, GetNextScheduledWakeUpImpl());
 }
 
-void TaskQueueImpl::SetScheduledTimeDomainWakeUp(
-    base::Optional<base::TimeTicks> scheduled_time_domain_wake_up) {
-  main_thread_only().scheduled_time_domain_wake_up =
-      scheduled_time_domain_wake_up;
-
-  // If queue has immediate work an appropriate notification has already
-  // been issued.
-  if (!scheduled_time_domain_wake_up ||
-      main_thread_only().on_next_wake_up_changed_callback.is_null() ||
-      HasPendingImmediateWork())
+void TaskQueueImpl::UpdateDelayedWakeUpImpl(
+    LazyNow* lazy_now,
+    base::Optional<TaskQueueImpl::DelayedWakeUp> wake_up) {
+  if (main_thread_only().scheduled_wake_up == wake_up)
     return;
+  main_thread_only().scheduled_wake_up = wake_up;
 
-  main_thread_only().on_next_wake_up_changed_callback.Run(
-      scheduled_time_domain_wake_up.value());
+  if (wake_up &&
+      !main_thread_only().on_next_wake_up_changed_callback.is_null() &&
+      !HasPendingImmediateWork()) {
+    main_thread_only().on_next_wake_up_changed_callback.Run(wake_up->time);
+  }
+
+  main_thread_only().time_domain->ScheduleWakeUpForQueue(this, wake_up,
+                                                         lazy_now);
+}
+
+void TaskQueueImpl::SetDelayedWakeUpForTesting(
+    base::Optional<TaskQueueImpl::DelayedWakeUp> wake_up) {
+  LazyNow lazy_now = main_thread_only().time_domain->CreateLazyNow();
+  UpdateDelayedWakeUpImpl(&lazy_now, wake_up);
 }
 
 bool TaskQueueImpl::HasPendingImmediateWork() {

third_party/WebKit/Source/platform/scheduler/base/task_queue_impl.h

@@ -75,6 +75,14 @@ class PLATFORM_EXPORT TaskQueueImpl {
     base::TimeTicks time;
     int sequence_num;
 
+    bool operator!=(const DelayedWakeUp& other) const {
+      return time != other.time || other.sequence_num != sequence_num;
+    }
+
+    bool operator==(const DelayedWakeUp& other) const {
+      return !(*this != other);
+    }
+
     bool operator<=(const DelayedWakeUp& other) const {
       if (time == other.time) {
         // Debug gcc builds can compare an element against itself.
@@ -166,6 +174,7 @@ class PLATFORM_EXPORT TaskQueueImpl {
   size_t GetNumberOfPendingTasks() const;
   bool HasTaskToRunImmediately() const;
   base::Optional<base::TimeTicks> GetNextScheduledWakeUp();
+  base::Optional<DelayedWakeUp> GetNextScheduledWakeUpImpl();
   void SetQueuePriority(TaskQueue::QueuePriority priority);
   TaskQueue::QueuePriority GetQueuePriority() const;
   void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
@@ -200,14 +209,6 @@ class PLATFORM_EXPORT TaskQueueImpl {
   void NotifyWillProcessTask(const base::PendingTask& pending_task);
   void NotifyDidProcessTask(const base::PendingTask& pending_task);
 
-  // Called by TimeDomain when the wake-up for this queue has changed.
-  // There is only one wake-up, new wake-up cancels any previous wake-ups.
-  // If |scheduled_time_domain_wake_up| is base::nullopt then the wake-up
-  // has been cancelled.
-  // Must be called from the main thread.
-  void SetScheduledTimeDomainWakeUp(
-      base::Optional<base::TimeTicks> scheduled_time_domain_wake_up);
-
   // Check for available tasks in immediate work queues.
   // Used to check if we need to generate notifications about delayed work.
   bool HasPendingImmediateWork();
@@ -229,13 +230,9 @@ class PLATFORM_EXPORT TaskQueueImpl {
   }
 
   // Enqueues any delayed tasks which should be run now on the
-  // |delayed_work_queue|. Returns the subsequent wake-up that is required, if
-  // any. Must be called from the main thread.
-  base::Optional<DelayedWakeUp> WakeUpForDelayedWork(LazyNow* lazy_now);
-
-  base::Optional<base::TimeTicks> scheduled_time_domain_wake_up() const {
-    return main_thread_only().scheduled_time_domain_wake_up;
-  }
+  // |delayed_work_queue|.
+  // Must be called from the main thread.
+  void WakeUpForDelayedWork(LazyNow* lazy_now);
 
   HeapHandle heap_handle() const { return main_thread_only().heap_handle; }
 
@@ -296,6 +293,9 @@ class PLATFORM_EXPORT TaskQueueImpl {
   // constructed due to not having TaskQueue.
   void SetQueueEnabledForTest(bool enabled);
 
+ protected:
+  void SetDelayedWakeUpForTesting(base::Optional<DelayedWakeUp> wake_up);
+
  private:
   friend class WorkQueue;
   friend class WorkQueueTest;
@@ -340,9 +340,11 @@ class PLATFORM_EXPORT TaskQueueImpl {
     base::trace_event::BlameContext* blame_context;  // Not owned.
     EnqueueOrder current_fence;
     base::Optional<base::TimeTicks> delayed_fence;
-    base::Optional<base::TimeTicks> scheduled_time_domain_wake_up;
     OnTaskStartedHandler on_task_started_handler;
     OnTaskCompletedHandler on_task_completed_handler;
+    // Last reported wake up, used only in UpdateWakeUp to avoid
+    // excessive calls.
+    base::Optional<DelayedWakeUp> scheduled_wake_up;
     // If false, queue will be disabled. Used only for tests.
     bool is_enabled_for_test;
   };
@@ -392,7 +394,9 @@ class PLATFORM_EXPORT TaskQueueImpl {
   void EnableOrDisableWithSelector(bool enable);
 
   // Schedules delayed work on time domain and calls the observer.
-  void ScheduleDelayedWorkInTimeDomain(base::TimeTicks now);
+  void UpdateDelayedWakeUp(LazyNow* lazy_now);
+  void UpdateDelayedWakeUpImpl(LazyNow* lazy_now,
+                               base::Optional<DelayedWakeUp> wake_up);
 
   // Activate a delayed fence if a time has come.
   void ActivateDelayedFenceIfNeeded(base::TimeTicks now);

third_party/WebKit/Source/platform/scheduler/base/time_domain.cc

@@ -27,57 +27,49 @@ void TimeDomain::UnregisterQueue(internal::TaskQueueImpl* queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK_EQ(queue->GetTimeDomain(), this);
 
-  CancelDelayedWork(queue);
+  LazyNow lazy_now = CreateLazyNow();
+  ScheduleWakeUpForQueue(queue, base::nullopt, &lazy_now);
 }
 
-void TimeDomain::ScheduleDelayedWork(
+void TimeDomain::ScheduleWakeUpForQueue(
     internal::TaskQueueImpl* queue,
-    internal::TaskQueueImpl::DelayedWakeUp wake_up,
-    base::TimeTicks now) {
+    base::Optional<internal::TaskQueueImpl::DelayedWakeUp> wake_up,
+    LazyNow* lazy_now) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK_EQ(queue->GetTimeDomain(), this);
-  DCHECK(queue->IsQueueEnabled());
-  // We only want to store a single wake-up per queue, so we need to remove any
-  // previously registered wake up for |queue|.
-  if (queue->heap_handle().IsValid()) {
-    DCHECK(queue->scheduled_time_domain_wake_up());
+  DCHECK(queue->IsQueueEnabled() || !wake_up);
+
+  base::Optional<base::TimeTicks> previous_wake_up;
+  if (!delayed_wake_up_queue_.empty())
+    previous_wake_up = delayed_wake_up_queue_.Min().wake_up.time;
 
+  if (wake_up) {
+    // Insert a new wake-up into the heap.
+    if (queue->heap_handle().IsValid()) {
       // O(log n)
-    delayed_wake_up_queue_.ChangeKey(queue->heap_handle(), {wake_up, queue});
+      delayed_wake_up_queue_.ChangeKey(queue->heap_handle(),
+                                       {wake_up.value(), queue});
     } else {
       // O(log n)
-    delayed_wake_up_queue_.insert({wake_up, queue});
+      delayed_wake_up_queue_.insert({wake_up.value(), queue});
+    }
+  } else {
+    // Remove a wake-up from heap if present.
+    if (queue->heap_handle().IsValid())
+      delayed_wake_up_queue_.erase(queue->heap_handle());
   }
 
-  queue->SetScheduledTimeDomainWakeUp(wake_up.time);
-
-  // If |queue| is the first wake-up then request the wake-up.
-  if (delayed_wake_up_queue_.Min().queue == queue)
-    RequestWakeUpAt(now, wake_up.time);
-}
-
-void TimeDomain::CancelDelayedWork(internal::TaskQueueImpl* queue) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  DCHECK_EQ(queue->GetTimeDomain(), this);
+  base::Optional<base::TimeTicks> new_wake_up;
+  if (!delayed_wake_up_queue_.empty())
+    new_wake_up = delayed_wake_up_queue_.Min().wake_up.time;
 
-  // If no wake-up has been requested then bail out.
-  if (!queue->heap_handle().IsValid())
+  if (previous_wake_up == new_wake_up)
     return;
 
-  DCHECK(queue->scheduled_time_domain_wake_up());
-  DCHECK(!delayed_wake_up_queue_.empty());
-  base::TimeTicks prev_first_wake_up =
-      delayed_wake_up_queue_.Min().wake_up.time;
-
-  // O(log n)
-  delayed_wake_up_queue_.erase(queue->heap_handle());
-
-  if (delayed_wake_up_queue_.empty()) {
-    CancelWakeUpAt(prev_first_wake_up);
-  } else if (prev_first_wake_up != delayed_wake_up_queue_.Min().wake_up.time) {
-    CancelWakeUpAt(prev_first_wake_up);
-    RequestWakeUpAt(Now(), delayed_wake_up_queue_.Min().wake_up.time);
-  }
+  if (previous_wake_up)
+    CancelWakeUpAt(previous_wake_up.value());
+  if (new_wake_up)
+    RequestWakeUpAt(lazy_now->Now(), new_wake_up.value());
 }
 
 void TimeDomain::WakeUpReadyDelayedQueues(LazyNow* lazy_now) {
@@ -88,18 +80,7 @@ void TimeDomain::WakeUpReadyDelayedQueues(LazyNow* lazy_now) {
   while (!delayed_wake_up_queue_.empty() &&
          delayed_wake_up_queue_.Min().wake_up.time <= lazy_now->Now()) {
     internal::TaskQueueImpl* queue = delayed_wake_up_queue_.Min().queue;
-    base::Optional<internal::TaskQueueImpl::DelayedWakeUp> next_wake_up =
     queue->WakeUpForDelayedWork(lazy_now);
-
-    if (next_wake_up) {
-      // O(log n)
-      delayed_wake_up_queue_.ReplaceMin({*next_wake_up, queue});
-      queue->SetScheduledTimeDomainWakeUp(next_wake_up->time);
-    } else {
-      // O(log n)
-      delayed_wake_up_queue_.Pop();
-      DCHECK(!queue->scheduled_time_domain_wake_up());
-    }
   }
 }
 

third_party/WebKit/Source/platform/scheduler/base/time_domain.h

@@ -69,16 +69,10 @@ class PLATFORM_EXPORT TimeDomain {
   // the next task was posted to and it returns true.  Returns false otherwise.
   bool NextScheduledTaskQueue(internal::TaskQueueImpl** out_task_queue) const;
 
-  // Schedules a call to TaskQueueImpl::WakeUpForDelayedWork when this
-  // TimeDomain reaches |delayed_run_time|.  This supersedes any previously
-  // registered wake-up for |queue|.
-  void ScheduleDelayedWork(internal::TaskQueueImpl* queue,
-                           internal::TaskQueueImpl::DelayedWakeUp wake_up,
-                           base::TimeTicks now);
-
-  // Cancels any scheduled calls to TaskQueueImpl::WakeUpForDelayedWork for
-  // |queue|.
-  void CancelDelayedWork(internal::TaskQueueImpl* queue);
+  void ScheduleWakeUpForQueue(
+      internal::TaskQueueImpl* queue,
+      base::Optional<internal::TaskQueueImpl::DelayedWakeUp> wake_up,
+      LazyNow* lazy_now);
 
   // Registers the |queue|.
   void RegisterQueue(internal::TaskQueueImpl* queue);
@@ -132,9 +126,6 @@ class PLATFORM_EXPORT TimeDomain {
     void ClearHeapHandle() {
       DCHECK(queue->heap_handle().IsValid());
       queue->set_heap_handle(HeapHandle());
-
-      DCHECK(queue->scheduled_time_domain_wake_up());
-      queue->SetScheduledTimeDomainWakeUp(base::nullopt);
     }
   };