[Try # 3] Scheduler refactoring to virtually eliminate redundant DoWorks

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

 // 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.
 
 #ifndef THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_
 
 #include <map>
 
 #include "base/atomic_sequence_num.h"
+#include "base/cancelable_callback.h"
 #include "base/debug/task_annotator.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/pending_task.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "platform/scheduler/base/enqueue_order.h"
+#include "platform/scheduler/base/moveable_auto_lock.h"
 #include "platform/scheduler/base/task_queue_impl.h"
 #include "platform/scheduler/base/task_queue_selector.h"
 
 namespace base {
 namespace trace_event {
 class ConvertableToTraceFormat;
 }  // namespace trace_event
 }  // namespace base
 
 namespace blink {
@@ skipping 123 matching lines @@
   friend class internal::TaskQueueImpl;
   friend class TaskQueueManagerTest;
 
   class DeletionSentinel : public base::RefCounted<DeletionSentinel> {
    private:
     friend class base::RefCounted<DeletionSentinel>;
     ~DeletionSentinel() {}
   };
 
   // Unregisters a TaskQueue previously created by |NewTaskQueue()|.
-  // NOTE we have to flush the queue from |newly_updatable_| which means as a
-  // side effect MoveNewlyUpdatableQueuesIntoUpdatableQueueSet is called by this
-  // function.
   void UnregisterTaskQueue(scoped_refptr<internal::TaskQueueImpl> task_queue);
 
   // TaskQueueSelector::Observer implementation:
   void OnTaskQueueEnabled(internal::TaskQueueImpl* queue) override;
   void OnTriedToSelectBlockedWorkQueue(
       internal::WorkQueue* work_queue) override;
 
   // base::MessageLoop::NestingObserver implementation:
   void OnBeginNestedMessageLoop() override;
 
   // Called by the task queue to register a new pending task.
   void DidQueueTask(const internal::TaskQueueImpl::Task& pending_task);
 
   // Use the selector to choose a pending task and run it.
-  void DoWork(base::TimeTicks run_time, bool from_main_thread);
+  void DoWork(bool delayed);
+
+  // Post a DoWork continuation if |next_delay| is not empty.
+  void PostDoWorkContinuationLocked(base::Optional<base::TimeDelta> next_delay,
+                                    LazyNow* lazy_now,
+                                    MoveableAutoLock&& lock);
 
   // Delayed Tasks with run_times <= Now() are enqueued onto the work queue and
   // reloads any empty work queues.
   void WakeupReadyDelayedQueues(LazyNow* lazy_now);
 
   // Chooses the next work queue to service. Returns true if |out_queue|
   // indicates the queue from which the next task should be run, false to
   // avoid running any tasks.
   bool SelectWorkQueueToService(internal::WorkQueue** out_work_queue);
 
@@ skipping 15 matching lines @@
 
   bool RunsTasksOnCurrentThread() const;
   bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
                                   const base::Closure& task,
                                   base::TimeDelta delay);
 
   internal::EnqueueOrder GetNextSequenceNumber();
 
   // Calls DelayTillNextTask on all time domains and returns the smallest delay
   // requested if any.
-  base::Optional<base::TimeDelta> ComputeDelayTillNextTask(LazyNow* lazy_now);
+  base::Optional<base::TimeDelta> ComputeDelayTillNextTaskLocked(
+      LazyNow* lazy_now);
 
   void MaybeRecordTaskDelayHistograms(
       const internal::TaskQueueImpl::Task& pending_task,
       const internal::TaskQueueImpl* queue);
 
   std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
   AsValueWithSelectorResult(bool should_run,
                             internal::WorkQueue* selected_work_queue) const;
 
+  void MaybeScheduleImmediateWorkLocked(
+      const tracked_objects::Location& from_here,
+      MoveableAutoLock&& lock);
+
   // Adds |queue| to |any_thread().has_incoming_immediate_work_| and if
   // |queue_is_blocked| is false it makes sure a DoWork is posted.
   // Can be called from any thread.
   void OnQueueHasIncomingImmediateWork(internal::TaskQueueImpl* queue,
                                        bool queue_is_blocked);
 
   // Calls |ReloadImmediateWorkQueueIfEmpty| on all queues in
   // |queues_to_reload|.
   void ReloadEmptyWorkQueues(const std::unordered_set<internal::TaskQueueImpl*>&
                                  queues_to_reload) const;
 
   std::set<TimeDomain*> time_domains_;
   std::unique_ptr<RealTimeDomain> real_time_domain_;
 
   std::set<scoped_refptr<internal::TaskQueueImpl>> queues_;
 
   // We have to be careful when deleting a queue because some of the code uses
   // raw pointers and doesn't expect the rug to be pulled out from underneath.
   std::set<scoped_refptr<internal::TaskQueueImpl>> queues_to_delete_;
 
   internal::EnqueueOrderGenerator enqueue_order_generator_;
   base::debug::TaskAnnotator task_annotator_;
 
   base::ThreadChecker main_thread_checker_;
   scoped_refptr<TaskQueueManagerDelegate> delegate_;
   internal::TaskQueueSelector selector_;
 
-  base::Closure from_main_thread_immediate_do_work_closure_;
-  base::Closure from_other_thread_immediate_do_work_closure_;
+  base::Closure immediate_do_work_closure_;
+  base::Closure delayed_do_work_closure_;
 
   bool task_was_run_on_quiescence_monitored_queue_;
 
-  // To reduce locking overhead we track pending calls to DoWork separately for
-  // the main thread and other threads.
-  std::set<base::TimeTicks> main_thread_pending_wakeups_;
-
   struct AnyThread {
     AnyThread();
 
     // Set of task queues with newly available work on the incoming queue.
     std::unordered_set<internal::TaskQueueImpl*> has_incoming_immediate_work;
 
-    bool other_thread_pending_wakeup;
+    int do_work_running_count;
+    int immediate_do_work_posted_count;
+    bool is_nested;  // Whether or not the message loop is currently nested.
   };
 
   // TODO(alexclarke): Add a MainThreadOnly struct too.
 
   mutable base::Lock any_thread_lock_;
   AnyThread any_thread_;
 
   struct AnyThread& any_thread() {
     any_thread_lock_.AssertAcquired();
     return any_thread_;
   }
   const struct AnyThread& any_thread() const {
     any_thread_lock_.AssertAcquired();
     return any_thread_;
   }
 
+  base::TimeTicks next_delayed_do_work_;

[Sami, 2017/01/26 12:29:17]

nit: Should we call this next_delayed_do_work_time_,
next_posted_delayed_do_work_ or something to make the purpose a little more
obvious and match the other names better (e.g., *_closure)?

[alex clarke (OOO till 29th), 2017/01/26 15:22:38]

Done.

+  base::CancelableClosure cancelable_delayed_do_work_closure_;

[Sami, 2017/01/26 12:29:17]

Mind moving this next to |delayed_do_work_closure_| since they're pretty
related?

[alex clarke (OOO till 29th), 2017/01/26 15:22:38]

Done.

+
   bool record_task_delay_histograms_;
 
   int work_batch_size_;
   size_t task_count_;
 
   base::ObserverList<base::MessageLoop::TaskObserver> task_observers_;
 
   base::ObserverList<TaskTimeObserver> task_time_observers_;
 
   const char* tracing_category_;
   const char* disabled_by_default_tracing_category_;
   const char* disabled_by_default_verbose_tracing_category_;
 
   internal::TaskQueueImpl* currently_executing_task_queue_;  // NOT OWNED
 
   Observer* observer_;  // NOT OWNED
   scoped_refptr<DeletionSentinel> deletion_sentinel_;
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TASK_QUEUE_MANAGER_H_