Adds a flag to support "Virtual Time" to the blink scheduler

components/scheduler/base/task_queue_manager.cc

 // 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.
 
 #include "components/scheduler/base/task_queue_manager.h"
 
 #include <queue>
 #include <set>
 
 #include "base/bind.h"
-#include "base/time/default_tick_clock.h"
 #include "components/scheduler/base/lazy_now.h"
 #include "components/scheduler/base/nestable_single_thread_task_runner.h"
 #include "components/scheduler/base/task_queue_impl.h"
 #include "components/scheduler/base/task_queue_selector.h"
 #include "components/scheduler/base/task_queue_sets.h"
 
 namespace {
 const int64_t kMaxTimeTicks = std::numeric_limits<int64>::max();
 }
 
 namespace scheduler {
 
 TaskQueueManager::TaskQueueManager(
     scoped_refptr<NestableSingleThreadTaskRunner> main_task_runner,
     const char* tracing_category,
     const char* disabled_by_default_tracing_category,
     const char* disabled_by_default_verbose_tracing_category)
     : main_task_runner_(main_task_runner),
       task_was_run_on_quiescence_monitored_queue_(false),
       pending_dowork_count_(0),
       work_batch_size_(1),
-      time_source_(new base::DefaultTickClock),
       tracing_category_(tracing_category),
       disabled_by_default_tracing_category_(
           disabled_by_default_tracing_category),
       disabled_by_default_verbose_tracing_category_(
           disabled_by_default_verbose_tracing_category),
       observer_(nullptr),
       deletion_sentinel_(new DeletionSentinel()),
       weak_factory_(this) {
   DCHECK(main_task_runner->RunsTasksOnCurrentThread());
   TRACE_EVENT_OBJECT_CREATED_WITH_ID(disabled_by_default_tracing_category,
@@ skipping 124 matching lines @@
     newly_updatable_.pop_back();
   }
 }
 
 void TaskQueueManager::UpdateWorkQueues(
     bool should_trigger_wakeup,
     const internal::TaskQueueImpl::Task* previous_task) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   TRACE_EVENT0(disabled_by_default_tracing_category_,
                "TaskQueueManager::UpdateWorkQueues");
-  internal::LazyNow lazy_now(this);
+  internal::LazyNow lazy_now(tick_clock());
 
   // Move any ready delayed tasks into the incomming queues.
   WakeupReadyDelayedQueues(&lazy_now);
 
   MoveNewlyUpdatableQueuesIntoUpdatableQueueSet();
 
   auto iter = updatable_queue_set_.begin();
   while (iter != updatable_queue_set_.end()) {
     internal::TaskQueueImpl* queue = *iter++;
     // NOTE Update work queue may erase itself from |updatable_queue_set_|.
     // This is fine, erasing an element won't invalidate any interator, as long
     // as the iterator isn't the element being delated.
     if (queue->work_queue().empty())
       queue->UpdateWorkQueue(&lazy_now, should_trigger_wakeup, previous_task);
   }
 }
 
 void TaskQueueManager::ScheduleDelayedWorkTask(
     scoped_refptr<internal::TaskQueueImpl> queue,
     base::TimeTicks delayed_run_time) {
-  internal::LazyNow lazy_now(this);
+  internal::LazyNow lazy_now(tick_clock());
   ScheduleDelayedWork(queue.get(), delayed_run_time, &lazy_now);
 }
 
 void TaskQueueManager::ScheduleDelayedWork(internal::TaskQueueImpl* queue,
                                            base::TimeTicks delayed_run_time,
                                            internal::LazyNow* lazy_now) {
   if (!main_task_runner_->BelongsToCurrentThread()) {
     // NOTE posting a delayed task from a different thread is not expected to be
     // common. This pathway is less optimal than perhaps it could be because
     // it causes two main thread tasks to be run.  Should this assumption prove
@@ skipping 15 matching lines @@
     main_task_runner_->PostDelayedTask(FROM_HERE, delayed_queue_wakeup_closure_,
                                        delay);
   }
   delayed_wakeup_multimap_.insert(std::make_pair(delayed_run_time, queue));
 }
 
 void TaskQueueManager::DelayedDoWork() {
   DCHECK(main_thread_checker_.CalledOnValidThread());
 
   {
-    internal::LazyNow lazy_now(this);
+    internal::LazyNow lazy_now(tick_clock());
     WakeupReadyDelayedQueues(&lazy_now);
   }
 
   DoWork(false);
 }
 
 void TaskQueueManager::WakeupReadyDelayedQueues(internal::LazyNow* lazy_now) {
   // Wake up any queues with pending delayed work.  Note std::multipmap stores
   // the elements sorted by key, so the begin() iterator points to the earliest
   // queue to wakeup.
@@ skipping 66 matching lines @@
 
     // Only run a single task per batch in nested run loops so that we can
     // properly exit the nested loop when someone calls RunLoop::Quit().
     if (main_task_runner_->IsNested())
       break;
   }
 
   // TODO(alexclarke): Consider refactoring the above loop to terminate only
   // when there's no more work left to be done, rather than posting a
   // continuation task.
-  if (!selector_.EnabledWorkQueuesEmpty())
+  if (!selector_.EnabledWorkQueuesEmpty()) {
     MaybePostDoWorkOnMainRunner();
+  } else {
+    // Tell the task runner we have no more work.
+    main_task_runner_->OnNoMoreWork();
+  }
 }
 
 bool TaskQueueManager::SelectQueueToService(
     internal::TaskQueueImpl** out_queue) {
   bool should_run = selector_.SelectQueueToService(out_queue);
   TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(
       disabled_by_default_tracing_category_, "TaskQueueManager", this,
       AsValueWithSelectorResult(should_run, *out_queue));
   return should_run;
 }
@@ skipping 74 matching lines @@
   DCHECK(main_thread_checker_.CalledOnValidThread());
   task_observers_.AddObserver(task_observer);
 }
 
 void TaskQueueManager::RemoveTaskObserver(
     base::MessageLoop::TaskObserver* task_observer) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   task_observers_.RemoveObserver(task_observer);
 }
 
-void TaskQueueManager::SetTimeSourceForTesting(
-    scoped_ptr<base::TickClock> time_source) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  time_source_ = time_source.Pass();
-}
-
 bool TaskQueueManager::GetAndClearSystemIsQuiescentBit() {
   bool task_was_run = task_was_run_on_quiescence_monitored_queue_;
   task_was_run_on_quiescence_monitored_queue_ = false;
   return !task_was_run;
 }
 
-base::TimeTicks TaskQueueManager::Now() const {
-  return time_source_->NowTicks();
+base::TickClock* TaskQueueManager::tick_clock() const {
+  return main_task_runner_.get();
 }
 
 int TaskQueueManager::GetNextSequenceNumber() {
   return task_sequence_num_.GetNext();
 }
 
 scoped_refptr<base::trace_event::ConvertableToTraceFormat>
 TaskQueueManager::AsValueWithSelectorResult(
     bool should_run,
     internal::TaskQueueImpl* selected_queue) const {
@@ skipping 18 matching lines @@
 }
 
 void TaskQueueManager::OnTaskQueueEnabled(internal::TaskQueueImpl* queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   // Only schedule DoWork if there's something to do.
   if (!queue->work_queue().empty())
     MaybePostDoWorkOnMainRunner();
 }
 
 }  // namespace scheduler