scheduler: Implement task observers

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/message_loop/message_loop.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 trace_event {
 class ConvertableToTraceFormat;
 class TracedValue;
@@ skipping 61 matching lines @@
   // 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);
 
+  // These functions can only be called on the same thread that the task queue
+  // manager executes its tasks on.
+  void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
+  void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
+
   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.
   // |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);
+  // |queue_index|. |first_task_in_batch| should be true if this the first task
+  // we are executing in the current work batch. Non-nestable task are reposted
+  // on the run loop. The queue must not be empty.
+  void ProcessTaskFromWorkQueue(size_t queue_index, bool first_task_in_batch);
 
   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;
 
@@ skipping 13 matching lines @@
   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_;
 
+  ObserverList<base::MessageLoop::TaskObserver> task_observers_;
+
+  // Previously executed task. Only valid during a call to DoWork().
+  base::PendingTask previous_task_;
+
   base::WeakPtrFactory<TaskQueueManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskQueueManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_SCHEDULER_TASK_QUEUE_MANAGER_H_