[Approach 3] Pre-allocate IncomigTaskQueue before MessageLoop for faster thread startup

base/message_loop/incoming_task_queue.h

 // Copyright 2013 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 BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
 #define BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_
 
 #include "base/base_export.h"
+#include "base/debug/task_annotator.h"
 #include "base/memory/ref_counted.h"
 #include "base/pending_task.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class MessageLoop;
 class WaitableEvent;
 
 namespace internal {
 
 // Implements a queue of tasks posted to the message loop running on the current
 // thread. This class takes care of synchronizing posting tasks from different
 // threads and together with MessageLoop ensures clean shutdown.
 class BASE_EXPORT IncomingTaskQueue
     : public RefCountedThreadSafe<IncomingTaskQueue> {
  public:
-  explicit IncomingTaskQueue(MessageLoop* message_loop);
+  IncomingTaskQueue();
+
+  // Associates the |message_loop| to this task queue and starts scheduling
+  // tasks.
+  void StartScheduling(MessageLoop* message_loop);
 
   // Appends a task to the incoming queue. Posting of all tasks is routed though
   // AddToIncomingQueue() or TryAddToIncomingQueue() to make sure that posting
   // task is properly synchronized between different threads.
   //
   // Returns true if the task was successfully added to the queue, otherwise
   // returns false. In all cases, the ownership of |task| is transferred to the
   // called method.
   bool AddToIncomingQueue(const tracked_objects::Location& from_here,
                           const Closure& task,
                           TimeDelta delay,
                           bool nestable);
 
   // Returns true if the queue contains tasks that require higher than default
   // timer resolution. Currently only needed for Windows.
   bool HasHighResolutionTasks();
 
   // Returns true if the message loop is "idle". Provided for testing.
   bool IsIdleForTesting();
 
   // Loads tasks from the |incoming_queue_| into |*work_queue|. Must be called
   // from the thread that is running the loop. Returns the number of tasks that
   // require high resolution timers.
   int ReloadWorkQueue(TaskQueue* work_queue);
 
   // Disconnects |this| from the parent message loop.
   void WillDestroyCurrentMessageLoop();
 
+  // Returns the TaskAnnotator which is used to add debug information to posted
+  // tasks.
+  debug::TaskAnnotator* task_annotator() { return &task_annotator_; }
+
  private:
   friend class RefCountedThreadSafe<IncomingTaskQueue>;
   virtual ~IncomingTaskQueue();
 
   // Calculates the time at which a PendingTask should run.
   TimeTicks CalculateDelayedRuntime(TimeDelta delay);
 
   // Adds a task to |incoming_queue_|. The caller retains ownership of
   // |pending_task|, but this function will reset the value of
   // |pending_task->task|. This is needed to ensure that the posting call stack
@@ skipping 13 matching lines @@
   TaskQueue incoming_queue_;
 
   // Points to the message loop that owns |this|.
   MessageLoop* message_loop_;
 
   // The next sequence number to use for delayed tasks.
   int next_sequence_num_;
 
   // True if our message loop has already been scheduled and does not need to be
   // scheduled again until an empty reload occurs.
-  bool message_loop_scheduled_;
+  bool message_loop_scheduled_ = false;
+
+  // True after WillDestroyCurrentMessageLoop is called.
+  bool message_loop_terminated_ = false;
 
   // True if we always need to call ScheduleWork when receiving a new task, even
   // if the incoming queue was not empty.
-  const bool always_schedule_work_;
+  bool always_schedule_work_ = false;
+
+  debug::TaskAnnotator task_annotator_;
 
   DISALLOW_COPY_AND_ASSIGN(IncomingTaskQueue);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_INCOMING_TASK_QUEUE_H_