scheduler: Maintain a constant enqueue order for every task

third_party/WebKit/Source/platform/scheduler/base/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 THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_IMPL_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_IMPL_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 31 matching lines @@
 //    delayed_work_queue
 //
 // The immediate_incoming_queue can be accessed from any thread, the other
 // queues are main-thread only. To reduce the overhead of locking,
 // immediate_work_queue is swapped with immediate_incoming_queue when
 // immediate_work_queue becomes empty.
 //
 // Delayed tasks are initially posted to delayed_incoming_queue and a wake-up
 // is scheduled with the TimeDomain.  When the delay has elapsed, the TimeDomain
 // calls UpdateDelayedWorkQueue and ready delayed tasks are moved into the
-// delayed_work_queue.  Note the EnqueueOrder (used for ordering) for a delayed
-// task is not set until it's moved into the delayed_work_queue.
+// delayed_work_queue.
 //
 // TaskQueueImpl uses the WorkQueueSets and the TaskQueueSelector to implement
 // prioritization. Task selection is done by the TaskQueueSelector and when a
 // queue is selected, it round-robins between the immediate_work_queue and
 // delayed_work_queue.  The reason for this is we want to make sure delayed
 // tasks (normally the most common type) don't starve out immediate work.
 class BLINK_PLATFORM_EXPORT TaskQueueImpl final : public TaskQueue {
  public:
   TaskQueueImpl(TaskQueueManager* task_queue_manager,
                 TimeDomain* time_domain,
@@ skipping 14 matching lines @@
       }
       return time < other.time;
     }
   };
 
   class BLINK_PLATFORM_EXPORT Task : public base::PendingTask {
    public:
     Task();
     Task(const tracked_objects::Location& posted_from,
          base::OnceClosure task,
-         base::TimeTicks desired_run_time,
-         EnqueueOrder sequence_number,
+         EnqueueOrder enqueue_order,
          bool nestable);
 
     Task(const tracked_objects::Location& posted_from,
          base::OnceClosure task,
          base::TimeTicks desired_run_time,
          EnqueueOrder sequence_number,
          bool nestable,
          EnqueueOrder enqueue_order);
 
     DelayedWakeUp delayed_wake_up() const {
       return DelayedWakeUp{delayed_run_time, sequence_num};
     }
 
     EnqueueOrder enqueue_order() const {
-#ifndef NDEBUG
-      DCHECK(enqueue_order_set_);
-#endif
       return enqueue_order_;
     }
 
-    void set_enqueue_order(EnqueueOrder enqueue_order) {
-#ifndef NDEBUG
-      DCHECK(!enqueue_order_set_);
-      enqueue_order_set_ = true;
-#endif
-      enqueue_order_ = enqueue_order;
-    }
-
-#ifndef NDEBUG
-    bool enqueue_order_set() const { return enqueue_order_set_; }
-#endif
-
    private:
-#ifndef NDEBUG
-    bool enqueue_order_set_;
-#endif
     // Similar to sequence number, but ultimately the |enqueue_order_| is what
     // the scheduler uses for task ordering. For immediate tasks |enqueue_order|
     // is set when posted, but for delayed tasks it's not defined until they are
     // enqueued on the |delayed_work_queue_|. This is because otherwise delayed
     // tasks could run before an immediate task posted after the delayed task.
     EnqueueOrder enqueue_order_;
   };
 
   // TaskQueue implementation.
   void UnregisterTaskQueue() override;
@@ skipping 76 matching lines @@
         scheduled_time_domain_wake_up;
   }
 
   HeapHandle heap_handle() const { return main_thread_only().heap_handle; }
 
   void set_heap_handle(HeapHandle heap_handle) {
     main_thread_only().heap_handle = heap_handle;
   }
 
   void PushImmediateIncomingTaskForTest(TaskQueueImpl::Task&& task);
-  EnqueueOrder GetFenceForTest() const;
+  uint64_t GetFenceForTest() const;
 
   class QueueEnabledVoterImpl : public QueueEnabledVoter {
    public:
     explicit QueueEnabledVoterImpl(TaskQueueImpl* task_queue);
     ~QueueEnabledVoterImpl() override;
 
     // QueueEnabledVoter implementation.
     void SetQueueEnabled(bool enabled) override;
 
     TaskQueueImpl* GetTaskQueueForTest() const { return task_queue_.get(); }
@@ skipping 44 matching lines @@
 
     std::unique_ptr<WorkQueue> delayed_work_queue;
     std::unique_ptr<WorkQueue> immediate_work_queue;
     std::priority_queue<Task> delayed_incoming_queue;
     base::ObserverList<base::MessageLoop::TaskObserver> task_observers;
     size_t set_index;
     HeapHandle heap_handle;
     int is_enabled_refcount;
     int voter_refcount;
     base::trace_event::BlameContext* blame_context;  // Not owned.
-    EnqueueOrder current_fence;
+    uint64_t current_fence;
     base::TimeTicks scheduled_time_domain_wake_up;
   };
 
   ~TaskQueueImpl() override;
 
   bool PostImmediateTaskImpl(const tracked_objects::Location& from_here,
                              base::OnceClosure task,
                              TaskType task_type);
   bool PostDelayedTaskImpl(const tracked_objects::Location& from_here,
                            base::OnceClosure task,
@@ skipping 12 matching lines @@
   void ScheduleDelayedWorkTask(Task pending_task);
 
   void MoveReadyImmediateTasksToImmediateWorkQueueLocked();
 
   // Push the task onto the |immediate_incoming_queue| and for auto pumped
   // queues it calls MaybePostDoWorkOnMainRunner if the Incoming queue was
   // empty.
   void PushOntoImmediateIncomingQueueLocked(
       const tracked_objects::Location& posted_from,
       base::OnceClosure task,
-      base::TimeTicks desired_run_time,
-      EnqueueOrder sequence_number,
+      EnqueueOrder enqueue_order,
       bool nestable);
 
   // Extracts all the tasks from the immediate incoming queue and clears it.
   // Can be called from any thread.
   WTF::Deque<TaskQueueImpl::Task> TakeImmediateIncomingQueue();
 
   void TraceQueueSize() const;
   static void QueueAsValueInto(const WTF::Deque<Task>& queue,
                                base::trace_event::TracedValue* state);
   static void QueueAsValueInto(const std::priority_queue<Task>& queue,
@@ skipping 55 matching lines @@
   const bool should_report_when_execution_blocked_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueImpl);
 };
 
 }  // namespace internal
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_IMPL_H_