Handle delayed tasks more natively in the scheduler

content/renderer/scheduler/task_queue_manager.cc

Index: content/renderer/scheduler/task_queue_manager.cc
diff --git a/content/renderer/scheduler/task_queue_manager.cc b/content/renderer/scheduler/task_queue_manager.cc
index 565aece83c5d1fb909da95aa011abe296315561d..7a9c124c36f7b3068fa9b43c28a1a97896585ef5 100644
--- a/content/renderer/scheduler/task_queue_manager.cc
+++ b/content/renderer/scheduler/task_queue_manager.cc
@@ -5,6 +5,7 @@
 #include "content/renderer/scheduler/task_queue_manager.h"
 
 #include <queue>
+#include <set>
 
 #include "base/bind.h"
 #include "base/trace_event/trace_event.h"
@@ -20,6 +21,29 @@ const int64_t kMaxTimeTicks = std::numeric_limits<int64>::max();
 namespace content {
 namespace internal {
 
+// Now() is somewhat expensive so it makes sense not to call Now() unless we
+// really need to.
+class LazyNow {
+ public:
+  explicit LazyNow(base::TimeTicks now)
+      : task_queue_manager_(nullptr), now_(now) {
+    DCHECK(!now.is_null());
+  }
+
+  explicit LazyNow(TaskQueueManager* task_queue_manager)
+      : task_queue_manager_(task_queue_manager) {}
+
+  base::TimeTicks Now() {
+    if (now_.is_null())
+      now_ = task_queue_manager_->Now();
+    return now_;
+  }
+
+ private:
+  TaskQueueManager* task_queue_manager_;  // NOT OWNED
+  base::TimeTicks now_;
+};
+
 class TaskQueue : public base::SingleThreadTaskRunner {
  public:
   TaskQueue(TaskQueueManager* task_queue_manager);
@@ -46,7 +70,7 @@ class TaskQueue : public base::SingleThreadTaskRunner {
   bool NextPendingDelayedTaskRunTime(
       base::TimeTicks* next_pending_delayed_task);
 
-  bool UpdateWorkQueue(base::TimeTicks* next_pending_delayed_task,
+  bool UpdateWorkQueue(LazyNow* lazy_now,
                        const base::PendingTask* previous_task);
   base::PendingTask TakeTaskFromWorkQueue();
 
@@ -71,37 +95,47 @@ class TaskQueue : public base::SingleThreadTaskRunner {
                            base::TimeDelta delay,
                            TaskType task_type);
 
-  // Adds a task at the end of the incoming task queue and schedules a call to
-  // TaskQueueManager::DoWork() if the incoming queue was empty and automatic
-  // pumping is enabled. Can be called on an arbitrary thread.
-  void EnqueueTask(const base::PendingTask& pending_task);
+  // Delayed task posted to the underlying run loop, which locks |lock_| and
+  // calls MoveReadyDelayedTasksToIncomingQueueLocked to process dealyed tasks
+  // that need to be run now.
+  void MoveReadyDelayedTasksToIncomingQueue();
+
+  // Enqueues any delayed tasks which should be run now on the incoming_queue_
+  // and calls ScheduleDelayedWorkLocked to ensure future tasks are scheduled.
+  // Must be called with |lock_| locked.
+  void MoveReadyDelayedTasksToIncomingQueueLocked(LazyNow* lazy_now);
+
+  // Posts MoveReadyDelayedTasksToIncomingQueue if there isn't already a task
+  // posted on the underlying runloop for the next task's scheduled run time.
+  void ScheduleDelayedWorkLocked(LazyNow* lazy_now);
 
   void PumpQueueLocked();
   bool TaskIsOlderThanQueuedTasks(const base::PendingTask* task);
   bool ShouldAutoPumpQueueLocked(const base::PendingTask* previous_task);
   void EnqueueTaskLocked(const base::PendingTask& pending_task);
-  bool NextPendingDelayedTaskRunTimeLocked(
-      base::TimeTicks* next_pending_delayed_task);
 
   void TraceQueueSize(bool is_locked) const;
   static const char* PumpPolicyToString(
       TaskQueueManager::PumpPolicy pump_policy);
   static void QueueAsValueInto(const base::TaskQueue& queue,
                                base::trace_event::TracedValue* state);
+  static void QueueAsValueInto(const base::DelayedTaskQueue& queue,
+                               base::trace_event::TracedValue* state);
   static void TaskAsValueInto(const base::PendingTask& task,
                               base::trace_event::TracedValue* state);
 
-  // This lock protects all members except the work queue.
+  // This lock protects all members except the work queue and the
+  // main_thread_checker_.
   mutable base::Lock lock_;
   base::PlatformThreadId thread_id_;
   TaskQueueManager* task_queue_manager_;
   base::TaskQueue incoming_queue_;
   TaskQueueManager::PumpPolicy pump_policy_;
   const char* name_;
-  std::priority_queue<base::TimeTicks,
-                      std::vector<base::TimeTicks>,
-                      std::greater<base::TimeTicks>> delayed_task_run_times_;
+  base::DelayedTaskQueue delayed_task_queue_;
+  std::set<base::TimeTicks> in_flight_kick_delayed_tasks_;
 
+  base::ThreadChecker main_thread_checker_;
   base::TaskQueue work_queue_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueue);
@@ -120,6 +154,8 @@ TaskQueue::~TaskQueue() {
 void TaskQueue::WillDeleteTaskQueueManager() {
   base::AutoLock lock(lock_);
   task_queue_manager_ = nullptr;
+  // TODO(scheduler-dev): Should we also clear the other queues here too?
+  delayed_task_queue_ = base::DelayedTaskQueue();
 }
 
 bool TaskQueue::RunsTasksOnCurrentThread() const {
@@ -140,15 +176,66 @@ bool TaskQueue::PostDelayedTaskImpl(const tracked_objects::Location& from_here,
   task_queue_manager_->DidQueueTask(&pending_task);
 
   if (delay > base::TimeDelta()) {
-    pending_task.delayed_run_time = task_queue_manager_->Now() + delay;
-    delayed_task_run_times_.push(pending_task.delayed_run_time);
-    return task_queue_manager_->PostDelayedTask(
-        FROM_HERE, Bind(&TaskQueue::EnqueueTask, this, pending_task), delay);
+    base::TimeTicks now = task_queue_manager_->Now();
+    pending_task.delayed_run_time = now + delay;
+    delayed_task_queue_.push(pending_task);
+    TraceQueueSize(true);
+    // If we changed the topmost task, then it is time to reschedule.
+    if (delayed_task_queue_.top().task.Equals(pending_task.task)) {
+      LazyNow lazy_now(now);
+      ScheduleDelayedWorkLocked(&lazy_now);
+    }
+    return true;
   }
   EnqueueTaskLocked(pending_task);
   return true;
 }
 
+void TaskQueue::MoveReadyDelayedTasksToIncomingQueue() {
+  DCHECK(main_thread_checker_.CalledOnValidThread());
+  base::AutoLock lock(lock_);
+  if (!task_queue_manager_)
+    return;
+
+  LazyNow lazy_now(task_queue_manager_);
+  MoveReadyDelayedTasksToIncomingQueueLocked(&lazy_now);
+}
+
+void TaskQueue::MoveReadyDelayedTasksToIncomingQueueLocked(LazyNow* lazy_now) {
+  lock_.AssertAcquired();
+  // Enqueue all delayed tasks that should be running now.
+  while (!delayed_task_queue_.empty() &&
+         delayed_task_queue_.top().delayed_run_time <= lazy_now->Now()) {
+    in_flight_kick_delayed_tasks_.erase(
+        delayed_task_queue_.top().delayed_run_time);
+    EnqueueTaskLocked(delayed_task_queue_.top());
+    delayed_task_queue_.pop();
+  }
+  TraceQueueSize(true);
+  ScheduleDelayedWorkLocked(lazy_now);
+}
+
+void TaskQueue::ScheduleDelayedWorkLocked(LazyNow* lazy_now) {
+  lock_.AssertAcquired();
+  // Any remaining tasks are in the future, so queue a task to kick them.
+  if (!delayed_task_queue_.empty()) {
+    base::TimeTicks next_run_time = delayed_task_queue_.top().delayed_run_time;
+    DCHECK_GT(next_run_time, lazy_now->Now());
+    // Make sure we don't have more than one
+    // MoveReadyDelayedTasksToIncomingQueue posted for a particular scheduled
+    // run time (note it's fine to have multiple ones in flight for distinct
+    // run times).
+    if (in_flight_kick_delayed_tasks_.find(next_run_time) ==
+        in_flight_kick_delayed_tasks_.end()) {
+      in_flight_kick_delayed_tasks_.insert(next_run_time);
+      base::TimeDelta delay = next_run_time - lazy_now->Now();
+      task_queue_manager_->PostDelayedTask(
+          FROM_HERE,
+          Bind(&TaskQueue::MoveReadyDelayedTasksToIncomingQueue, this), delay);
+    }
+  }
+}
+
 bool TaskQueue::IsQueueEmpty() const {
   if (!work_queue_.empty())
     return false;
@@ -197,31 +284,23 @@ bool TaskQueue::ShouldAutoPumpQueueLocked(
 bool TaskQueue::NextPendingDelayedTaskRunTime(
     base::TimeTicks* next_pending_delayed_task) {
   base::AutoLock lock(lock_);
-  return NextPendingDelayedTaskRunTimeLocked(next_pending_delayed_task);
-}
-
-bool TaskQueue::NextPendingDelayedTaskRunTimeLocked(
-    base::TimeTicks* next_pending_delayed_task) {
-  lock_.AssertAcquired();
-  if (!delayed_task_run_times_.empty()) {
-    *next_pending_delayed_task =
-        std::min(*next_pending_delayed_task, delayed_task_run_times_.top());
-    return true;
-  }
-  return false;
+  if (delayed_task_queue_.empty())
+    return false;
+  *next_pending_delayed_task = delayed_task_queue_.top().delayed_run_time;
+  return true;
 }
 
-bool TaskQueue::UpdateWorkQueue(
-    base::TimeTicks* next_pending_delayed_task,
-    const base::PendingTask* previous_task) {
+bool TaskQueue::UpdateWorkQueue(LazyNow* lazy_now,
+                                const base::PendingTask* previous_task) {
   if (!work_queue_.empty())
     return true;
 
   {
     base::AutoLock lock(lock_);
-    NextPendingDelayedTaskRunTimeLocked(next_pending_delayed_task);
+    MoveReadyDelayedTasksToIncomingQueueLocked(lazy_now);
     if (!ShouldAutoPumpQueueLocked(previous_task))
       return false;
+    MoveReadyDelayedTasksToIncomingQueueLocked(lazy_now);
     work_queue_.Swap(&incoming_queue_);
     TraceQueueSize(true);
     return true;
@@ -245,17 +324,13 @@ void TaskQueue::TraceQueueSize(bool is_locked) const {
     lock_.Acquire();
   else
     lock_.AssertAcquired();
-  TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"), name_,
-                 incoming_queue_.size() + work_queue_.size());
+  TRACE_COUNTER1(
+      TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"), name_,
+      incoming_queue_.size() + work_queue_.size() + delayed_task_queue_.size());
   if (!is_locked)
     lock_.Release();
 }
 
-void TaskQueue::EnqueueTask(const base::PendingTask& pending_task) {
-  base::AutoLock lock(lock_);
-  EnqueueTaskLocked(pending_task);
-}
-
 void TaskQueue::EnqueueTaskLocked(const base::PendingTask& pending_task) {
   lock_.AssertAcquired();
   if (!task_queue_manager_)
@@ -266,11 +341,6 @@ void TaskQueue::EnqueueTaskLocked(const base::PendingTask& pending_task) {
   incoming_queue_.push(pending_task);
 
   if (!pending_task.delayed_run_time.is_null()) {
-    // Update the time of the next pending delayed task.
-    while (!delayed_task_run_times_.empty() &&
-           delayed_task_run_times_.top() <= pending_task.delayed_run_time) {
-      delayed_task_run_times_.pop();
-    }
     // Clear the delayed run time because we've already applied the delay
     // before getting here.
     incoming_queue_.back().delayed_run_time = base::TimeTicks();
@@ -289,6 +359,10 @@ void TaskQueue::SetPumpPolicy(TaskQueueManager::PumpPolicy pump_policy) {
 
 void TaskQueue::PumpQueueLocked() {
   lock_.AssertAcquired();
+  if (task_queue_manager_) {
+    LazyNow lazy_now(task_queue_manager_);
+    MoveReadyDelayedTasksToIncomingQueueLocked(&lazy_now);
+  }
   while (!incoming_queue_.empty()) {
     work_queue_.push(incoming_queue_.front());
     incoming_queue_.pop();
@@ -313,6 +387,8 @@ void TaskQueue::AsValueInto(base::trace_event::TracedValue* state) const {
   state->EndArray();
   state->BeginArray("work_queue");
   QueueAsValueInto(work_queue_, state);
+  state->BeginArray("delayed_task_queue");
+  QueueAsValueInto(delayed_task_queue_, state);
   state->EndArray();
   state->EndDictionary();
 }
@@ -344,6 +420,16 @@ void TaskQueue::QueueAsValueInto(const base::TaskQueue& queue,
 }
 
 // static
+void TaskQueue::QueueAsValueInto(const base::DelayedTaskQueue& queue,
+                                 base::trace_event::TracedValue* state) {
+  base::DelayedTaskQueue queue_copy(queue);
+  while (!queue_copy.empty()) {
+    TaskAsValueInto(queue_copy.top(), state);
+    queue_copy.pop();
+  }
+}
+
+// static
 void TaskQueue::TaskAsValueInto(const base::PendingTask& task,
                                 base::trace_event::TracedValue* state) {
   state->BeginDictionary();
@@ -416,8 +502,13 @@ base::TimeTicks TaskQueueManager::NextPendingDelayedTaskRunTime() {
   base::TimeTicks next_pending_delayed_task(
       base::TimeTicks::FromInternalValue(kMaxTimeTicks));
   for (auto& queue : queues_) {
-    found_pending_task |=
-        queue->NextPendingDelayedTaskRunTime(&next_pending_delayed_task);
+    base::TimeTicks queues_next_pending_delayed_task;
+    if (queue->NextPendingDelayedTaskRunTime(
+            &queues_next_pending_delayed_task)) {
+      found_pending_task = true;
+      next_pending_delayed_task =
+          std::min(next_pending_delayed_task, queues_next_pending_delayed_task);
+    }
   }
 
   if (!found_pending_task)
@@ -442,16 +533,15 @@ void TaskQueueManager::PumpQueue(size_t queue_index) {
 }
 
 bool TaskQueueManager::UpdateWorkQueues(
-    base::TimeTicks* next_pending_delayed_task,
     const base::PendingTask* previous_task) {
   // TODO(skyostil): This is not efficient when the number of queues grows very
   // large due to the number of locks taken. Consider optimizing when we get
   // there.
   DCHECK(main_thread_checker_.CalledOnValidThread());
+  internal::LazyNow lazy_now(this);
   bool has_work = false;
   for (auto& queue : queues_) {
-    has_work |= queue->UpdateWorkQueue(next_pending_delayed_task,
-                                       previous_task);
+    has_work |= queue->UpdateWorkQueue(&lazy_now, previous_task);
     if (!queue->work_queue().empty()) {
       // Currently we should not be getting tasks with delayed run times in any
       // of the work queues.
@@ -484,22 +574,14 @@ void TaskQueueManager::DoWork(bool posted_from_main_thread) {
   }
   DCHECK(main_thread_checker_.CalledOnValidThread());
 
-  base::TimeTicks next_pending_delayed_task(
-      base::TimeTicks::FromInternalValue(kMaxTimeTicks));
-
-  // Pass nullptr to UpdateWorkQueues here to prevent waking up an
+  // Pass nullptr to UpdateWorkQueues here to prevent waking up a
   // pump-after-wakeup queue.
-  if (!UpdateWorkQueues(&next_pending_delayed_task, nullptr))
+  if (!UpdateWorkQueues(nullptr))
     return;
 
   base::PendingTask previous_task((tracked_objects::Location()),
                                   (base::Closure()));
   for (int i = 0; i < work_batch_size_; i++) {
-    // Interrupt the work batch if we should run the next delayed task.
-    if (i > 0 && next_pending_delayed_task.ToInternalValue() != kMaxTimeTicks &&
-        Now() >= next_pending_delayed_task)
-      return;
-
     size_t queue_index;
     if (!SelectWorkQueueToService(&queue_index))
       return;
@@ -508,7 +590,7 @@ void TaskQueueManager::DoWork(bool posted_from_main_thread) {
     MaybePostDoWorkOnMainRunner();
     ProcessTaskFromWorkQueue(queue_index, i > 0, &previous_task);
 
-    if (!UpdateWorkQueues(&next_pending_delayed_task, &previous_task))
+    if (!UpdateWorkQueues(&previous_task))
       return;
   }
 }