[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/task_queue_impl.h"
 #include "platform/scheduler/base/task_queue_selector.h"
+#include "wtf/SpinLock.h"
 
 namespace base {
 namespace trace_event {
 class ConvertableToTraceFormat;
 }  // namespace trace_event
 }  // namespace base
 
 namespace blink {
 namespace scheduler {
 namespace internal {
@@ skipping 102 matching lines @@
     DCHECK(main_thread_checker_.CalledOnValidThread());
     return currently_executing_task_queue_;
   }
 
   // Return number of pending tasks in task queues.
   size_t GetNumberOfPendingTasks() const;
 
   // Returns true if there is a task that could be executed immediately.
   bool HasImmediateWorkForTesting() const;
 
+  // There is a small overhead to recording task delay histograms. If you don't
+  // need them, you can turn them off.
+  void SetRecordTaskDelayHistograms(bool record_task_delay_histograms);
+
  private:
   friend class LazyNow;
   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 PostDoWorkContinuation(base::Optional<base::TimeDelta> next_delay,
+                              LazyNow* lazy_now);
 
   // Delayed Tasks with run_times <= Now() are enqueued onto the work queue and
   // reloads any empty work queues.
-  void UpdateWorkQueues(LazyNow lazy_now);
+  void UpdateWorkQueues(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);
 
   // Runs a single nestable task from the |queue|. On exit, |out_task| will
   // contain the task which was executed. Non-nestable task are reposted on the
   // run loop. The queue must not be empty.
   enum class ProcessTaskResult {
     DEFERRED,
     EXECUTED,
     TASK_QUEUE_MANAGER_DELETED
   };
   ProcessTaskResult ProcessTaskFromWorkQueue(internal::WorkQueue* work_queue,
                                              LazyNow*);
 
   bool RunsTasksOnCurrentThread() const;
   bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
                                   const base::Closure& task,
                                   base::TimeDelta delay);
 
   internal::EnqueueOrder GetNextSequenceNumber();
 
-  // Calls MaybeAdvanceTime on all time domains and returns true if one of them
-  // was able to advance.
-  bool TryAdvanceTimeDomains();
+  // Calls DelayTillNextTask on all time domains and returns the smallest delay
+  // requested if any.
+  base::Optional<base::TimeDelta> DelayTillNextTask(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);
+
+  void MaybeScheduleDelayedWorkInternal(
+      const tracked_objects::Location& from_here,
+      base::TimeTicks now,
+      base::TimeDelta delay);
+
+  // Adds |queue| to |has_incomming_immediate_work_| and if
+  // |ensure_do_work_posted| is true it calls MaybeScheduleImmediateWorkLocked.
+  void OnQueueHasImmediateWork(internal::TaskQueueImpl* queue,
+                               bool ensure_do_work_posted);
+
+  void NotifyQueuesOfIncomingImmediateWorkOnMainThreadLocked();
+
   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_;
+  // Protects |do_work_running_count_|, |immediate_do_work_posted_count_|,
+  // |is_nested_| and |has_incomming_immediate_work_|.
+  mutable WTF::SpinLock do_work_pending_lock_;

[Sami, 2016/12/07 16:13:42]

nit: I think this could just be base::subtle::Spinlock since we already use base
locking primitives for everything else.

[alex clarke (OOO till 29th), 2016/12/08 17:38:49]

I'm actually thinking we should initially use a mutex and try a spinlock in a
subsequent patch.

+  int do_work_running_count_;

[Sami, 2016/12/07 16:13:43]

Should we wrap these into a struct like we do in the scheduler?

[alex clarke (OOO till 29th), 2016/12/08 17:38:48]

Good idea. Done.

+  int immediate_do_work_posted_count_;
+  std::set<internal::TaskQueueImpl*> has_incomming_immediate_work_;

[Sami, 2016/12/07 16:13:43]

typo: incoming

[alex clarke (OOO till 29th), 2016/12/08 17:38:48]

Done.

+  bool is_nested_;  // Whether or not the message loop is currently nested.
 
-  // Protects |other_thread_pending_wakeup_|.
-  mutable base::Lock other_thread_lock_;
-  bool other_thread_pending_wakeup_;
+  bool record_task_delay_histograms_;
+
+  base::TimeTicks next_delayed_do_work_;
+  base::CancelableClosure cancelable_delayed_do_work_closure_;
 
   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_