Reland: Explicitly track the scheduler task enqueueing order in a new field

components/scheduler/child/task_queue_impl.h

 // Copyright 2015 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 CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_IMPL_H_
 #define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_IMPL_H_
 
 #include <set>
 
 #include "base/pending_task.h"
 #include "base/threading/thread_checker.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "components/scheduler/child/lazy_now.h"
 #include "components/scheduler/child/task_queue.h"
 #include "components/scheduler/scheduler_export.h"
 
 namespace scheduler {
 class TaskQueueManager;
 
 namespace internal {
 
 class SCHEDULER_EXPORT TaskQueueImpl final : public TaskQueue {
  public:
   TaskQueueImpl(TaskQueueManager* task_queue_manager,
                 const Spec& spec,
                 const char* disabled_by_default_tracing_category,
                 const char* disabled_by_default_verbose_tracing_category);
 
+  class SCHEDULER_EXPORT Task : public base::PendingTask {
+   public:
+    Task();
+    Task(const tracked_objects::Location& posted_from,
+         const base::Closure& task,
+         int sequence_number,
+         bool nestable);
+
+    int enqueue_order() const {
+#ifndef NDEBUG
+      DCHECK(enqueue_order_set_);
+#endif
+      return enqueue_order_;
+    }
+
+    void set_enqueue_order(int enqueue_order) {
+#ifndef NDEBUG
+      DCHECK(!enqueue_order_set_);
+      enqueue_order_set_ = true;
+#endif
+      enqueue_order_ = enqueue_order;
+    }
+
+   private:
+#ifndef NDEBUG
+    bool enqueue_order_set_;
+#endif
+    // Similar to sequence number, but the |enqueue_order| is set by
+    // EnqueueTasksLocked and is not initially defined for delayed tasks until
+    // they are enqueued on the |incoming_queue_|.
+    int enqueue_order_;
+  };
+
   // TaskQueue implementation.
   bool RunsTasksOnCurrentThread() const override;
   bool PostDelayedTask(const tracked_objects::Location& from_here,
                        const base::Closure& task,
                        base::TimeDelta delay) override;
   bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
                                   const base::Closure& task,
                                   base::TimeDelta delay) override;
   bool PostDelayedTaskAt(const tracked_objects::Location& from_here,
                          const base::Closure& task,
                          base::TimeTicks desired_run_time) override;
 
   bool IsQueueEnabled() const override;
   QueueState GetQueueState() const override;
   void SetQueuePriority(QueuePriority priority) override;
   void PumpQueue() override;
   void SetPumpPolicy(PumpPolicy pump_policy) override;
 
   bool NextPendingDelayedTaskRunTime(
       base::TimeTicks* next_pending_delayed_task);
 
   void UpdateWorkQueue(LazyNow* lazy_now,
                        bool should_trigger_wakeup,
-                       const base::PendingTask* previous_task);
-  base::PendingTask TakeTaskFromWorkQueue();
+                       const Task* previous_task);
+  Task TakeTaskFromWorkQueue();
 
   void WillDeleteTaskQueueManager();
 
-  base::TaskQueue& work_queue() { return work_queue_; }
+  std::queue<Task>& work_queue() { return work_queue_; }
 
   WakeupPolicy wakeup_policy() const {
     DCHECK(main_thread_checker_.CalledOnValidThread());
     return wakeup_policy_;
   }
 
   const char* GetName() const override;
 
   void AsValueInto(base::trace_event::TracedValue* state) const;
 
   size_t get_task_queue_set_index() const { return set_index_; }
 
   void set_task_queue_set_index(size_t set_index) { set_index_ = set_index; }
 
-  // If the work queue isn't empty, |age| gets set to the sequence number of the
-  // front task and the dunctio returns true.  Otherwise the function returns
-  // false.
-  bool GetWorkQueueFrontTaskAge(int* age) const;
+  // If the work queue isn't empty, |enqueue_order| gets set to the enqueue
+  // order of the front task and the function returns true.  Otherwise the
+  // function returns false.
+  bool GetWorkQueueFrontTaskEnqueueOrder(int* enqueue_order) const;
 
   bool GetQuiescenceMonitored() const { return should_monitor_quiescence_; }
   bool GetShouldNotifyObservers() const { return should_notify_observers_; }
 
   // Test support functions.  These should not be used in production code.
-  void PushTaskOntoWorkQueueForTest(const base::PendingTask& task);
+  void PushTaskOntoWorkQueueForTest(const Task& task);
   void PopTaskFromWorkQueueForTest();
   size_t WorkQueueSizeForTest() const { return work_queue_.size(); }
 
   // Can be called on any thread.
   static const char* PumpPolicyToString(TaskQueue::PumpPolicy pump_policy);
 
   // Can be called on any thread.
   static const char* WakeupPolicyToString(
       TaskQueue::WakeupPolicy wakeup_policy);
 
@@ skipping 26 matching lines @@
   // 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 TaskIsOlderThanQueuedTasks(const Task* task);
   bool ShouldAutoPumpQueueLocked(bool should_trigger_wakeup,
-                                 const base::PendingTask* previous_task);
+                                 const Task* previous_task);
 
-  // Push the task onto the |incoming_queue_| and allocate a sequence number
-  // for it.
-  void EnqueueTaskLocked(const base::PendingTask& pending_task);
+  enum class EnqueueOrderPolicy { SET_ENQUEUE_ORDER, DONT_SET_ENQUEUE_ORDER };
+
+  // Push the task onto the |incoming_queue_| and maybe allocate an
+  // enqueue_order for it based on |enqueue_order_policy|.
+  void EnqueueTaskLocked(const Task& pending_task,
+                         EnqueueOrderPolicy enqueue_order_policy);
 
   void TraceQueueSize(bool is_locked) const;
-  static void QueueAsValueInto(const base::TaskQueue& queue,
+  static void QueueAsValueInto(const std::queue<Task>& queue,
                                base::trace_event::TracedValue* state);
-  static void QueueAsValueInto(const base::DelayedTaskQueue& queue,
+  static void QueueAsValueInto(const std::priority_queue<Task>& queue,
                                base::trace_event::TracedValue* state);
-  static void TaskAsValueInto(const base::PendingTask& task,
+  static void TaskAsValueInto(const Task& task,
                               base::trace_event::TracedValue* state);
 
   // This lock protects all members in the contigious block below.
   // TODO(alexclarke): Group all the members protected by the lock into a struct
   mutable base::Lock lock_;
   base::PlatformThreadId thread_id_;
   TaskQueueManager* task_queue_manager_;
-  base::TaskQueue incoming_queue_;
+  std::queue<Task> incoming_queue_;
   PumpPolicy pump_policy_;
-  // Queue-local task sequence number for maintaining the order of delayed
-  // tasks which are posted for the exact same time. Note that this will be
-  // replaced by the global sequence number when the delay has elapsed.
-  int delayed_task_sequence_number_;
-  base::DelayedTaskQueue delayed_task_queue_;
+  std::priority_queue<Task> delayed_task_queue_;
   std::set<base::TimeTicks> in_flight_kick_delayed_tasks_;
 
   const char* name_;
   const char* disabled_by_default_tracing_category_;
   const char* disabled_by_default_verbose_tracing_category_;
 
   base::ThreadChecker main_thread_checker_;
-  base::TaskQueue work_queue_;
+  std::queue<Task> work_queue_;
   WakeupPolicy wakeup_policy_;
   size_t set_index_;
   bool should_monitor_quiescence_;
   bool should_notify_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueImpl);
 };
 
 }  // namespace internal
 }  // namespace scheduler
 
 #endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_IMPL_H_