Run task queue manager work in batches

content/renderer/scheduler/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 CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
 #define CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_
 
 #include "base/atomic_sequence_num.h"
 #include "base/debug/task_annotator.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/pending_task.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
 
 namespace base {
 namespace debug {
 class ConvertableToTraceFormat;
 class TracedValue;
 }
 }
 
+namespace cc {
+class TestNowSource;
+}
+
 namespace content {
 namespace internal {
 class TaskQueue;
 }
 class TaskQueueSelector;
 
 // The task queue manager provides N task queues and a selector interface for
 // choosing which task queue to service next. Each task queue consists of two
 // sub queues:
 //
@@ skipping 38 matching lines @@
 
   // Returns true if there no tasks in either the work or incoming task queue
   // identified by |queue_index|. Note that this function involves taking a
   // lock, so calling it has some overhead.
   bool IsQueueEmpty(size_t queue_index) const;
 
   // Set the name |queue_index| for tracing purposes. |name| must be a pointer
   // to a static string.
   void SetQueueName(size_t queue_index, const char* name);
 
+  // Set the number of tasks executed in a single invocation of the task queue
+  // manager. Increasing the batch size can reduce the overhead of yielding
+  // back to the main message loop -- at the cost of potentially delaying other
+  // tasks posted to the main loop. The batch size is 1 by default.
+  void SetWorkBatchSize(int work_batch_size);
+
+  void SetTimeSourceForTesting(scoped_refptr<cc::TestNowSource> time_source);
+
  private:
   friend class internal::TaskQueue;
 
   // Called by the task queue to register a new pending task and allocate a
   // sequence number for it.
   void DidQueueTask(base::PendingTask* pending_task);
 
   // Post a task to call DoWork() on the main task runner.  Only one pending
   // DoWork is allowed from the main thread, to prevent an explosion of pending
   // DoWorks.
   void MaybePostDoWorkOnMainRunner();
 
   // Use the selector to choose a pending task and run it.
   void DoWork(bool posted_from_main_thread);
 
   // Reloads any empty work queues which have automatic pumping enabled.
   // Returns true if any work queue has tasks after doing this.
-  bool UpdateWorkQueues();
+  // |next_pending_delayed_task| should be the time of the next known delayed
+  // task. It is updated if any task is found which should run earlier.
+  bool UpdateWorkQueues(base::TimeTicks* next_pending_delayed_task);
 
   // Chooses the next work queue to service. Returns true if |out_queue_index|
   // indicates the queue from which the next task should be run, false to
   // avoid running any tasks.
   bool SelectWorkQueueToService(size_t* out_queue_index);
 
   // Runs a single nestable task from the work queue designated by
   // |queue_index|. Non-nestable task are reposted on the run loop.
   // The queue must not be empty.
   void ProcessTaskFromWorkQueue(size_t queue_index);
 
   bool RunsTasksOnCurrentThread() const;
   bool PostDelayedTask(const tracked_objects::Location& from_here,
                        const base::Closure& task,
                        base::TimeDelta delay);
   bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
                                   const base::Closure& task,
                                   base::TimeDelta delay);
   internal::TaskQueue* Queue(size_t queue_index) const;
 
+  base::TimeTicks Now() const;
+
   scoped_refptr<base::debug::ConvertableToTraceFormat>
   AsValueWithSelectorResult(bool should_run, size_t selected_queue) const;
 
   std::vector<scoped_refptr<internal::TaskQueue>> queues_;
   base::AtomicSequenceNumber task_sequence_num_;
   base::debug::TaskAnnotator task_annotator_;
 
   base::ThreadChecker main_thread_checker_;
   scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;
   TaskQueueSelector* selector_;
 
   base::WeakPtr<TaskQueueManager> task_queue_manager_weak_ptr_;
 
   // The pending_dowork_count_ is only tracked on the main thread since that's
   // where re-entrant problems happen.
   int pending_dowork_count_;
 
+  int work_batch_size_;
+
+  scoped_refptr<cc::TestNowSource> time_source_;
+
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_