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

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

Index: third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
diff --git a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
index 0fbfa7e12e62b6ad42849512d88b5ad089bbf1d9..073b1d1676319708435b3b1979e61d929befc8e4 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
+++ b/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.h
@@ -8,6 +8,7 @@
 #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"
@@ -18,6 +19,7 @@
 #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 {
@@ -140,6 +142,10 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   // 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;
@@ -152,9 +158,6 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   };
 
   // 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:
@@ -169,11 +172,15 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   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
@@ -198,9 +205,9 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
 
   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,
@@ -210,6 +217,21 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   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_;
 
@@ -226,18 +248,23 @@ class BLINK_PLATFORM_EXPORT TaskQueueManager
   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.
+
+  bool record_task_delay_histograms_;
 
-  // Protects |other_thread_pending_wakeup_|.
-  mutable base::Lock other_thread_lock_;
-  bool other_thread_pending_wakeup_;
+  base::TimeTicks next_delayed_do_work_;
+  base::CancelableClosure cancelable_delayed_do_work_closure_;
 
   int work_batch_size_;
   size_t task_count_;