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

base/message_loop/incoming_task_queue.cc

 // 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.
 
 #include "base/message_loop/incoming_task_queue.h"
 
 #include <limits>
 
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 21 matching lines @@
   // added
   // to the incoming queue.
   return type == MessageLoop::TYPE_UI || type == MessageLoop::TYPE_JAVA;
 #else
   return false;
 #endif
 }
 
 }  // namespace
 
-IncomingTaskQueue::IncomingTaskQueue(MessageLoop* message_loop)
+IncomingTaskQueue::IncomingTaskQueue()
     : high_res_task_count_(0),
-      message_loop_(message_loop),
-      next_sequence_num_(0),
-      message_loop_scheduled_(false),
-      always_schedule_work_(AlwaysNotifyPump(message_loop_->type())) {
+      message_loop_(nullptr),
+      next_sequence_num_(0) {
+}
+
+void IncomingTaskQueue::StartScheduling(MessageLoop* message_loop) {
+  AutoLock lock(incoming_queue_lock_);
+  DCHECK(!message_loop_);
+  DCHECK(!message_loop_terminated_);
+  DCHECK(message_loop);
+  message_loop_ = message_loop;
+  always_schedule_work_ = AlwaysNotifyPump(message_loop_->type());
+  if (!incoming_queue_.empty())
+    message_loop_->ScheduleWork();
 }
 
 bool IncomingTaskQueue::AddToIncomingQueue(
     const tracked_objects::Location& from_here,
     const Closure& task,
     TimeDelta delay,
     bool nestable) {
   DLOG_IF(WARNING,
           delay.InSeconds() > kTaskDelayWarningThresholdInSeconds)
       << "Requesting super-long task delay period of " << delay.InSeconds()
@@ skipping 42 matching lines @@
   }
   // Reset the count of high resolution tasks since our queue is now empty.
   int high_res_tasks = high_res_task_count_;
   high_res_task_count_ = 0;
   return high_res_tasks;
 }
 
 void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
   AutoLock lock(incoming_queue_lock_);
   message_loop_ = NULL;
+  message_loop_terminated_ = true;
 }
 
 IncomingTaskQueue::~IncomingTaskQueue() {
   // Verify that WillDestroyCurrentMessageLoop() has been called.
   DCHECK(!message_loop_);
+  DCHECK(message_loop_terminated_);
 }
 
 TimeTicks IncomingTaskQueue::CalculateDelayedRuntime(TimeDelta delay) {
   TimeTicks delayed_run_time;
   if (delay > TimeDelta())
     delayed_run_time = TimeTicks::Now() + delay;
   else
     DCHECK_EQ(delay.InMilliseconds(), 0) << "delay should not be negative";
   return delayed_run_time;
 }
 
 bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
   // Warning: Don't try to short-circuit, and handle this thread's tasks more
   // directly, as it could starve handling of foreign threads.  Put every task
   // into this queue.
 
   // This should only be called while the lock is taken.
   incoming_queue_lock_.AssertAcquired();
 
-  if (!message_loop_) {
+  if (message_loop_terminated_) {
     pending_task->task.Reset();
     return false;
   }
 
   // Initialize the sequence number. The sequence number is used for delayed
   // tasks (to faciliate FIFO sorting when two tasks have the same
   // delayed_run_time value) and for identifying the task in about:tracing.
   pending_task->sequence_num = next_sequence_num_++;
 
-  message_loop_->task_annotator()->DidQueueTask("MessageLoop::PostTask",
-                                                *pending_task);
+  task_annotator_.DidQueueTask("MessageLoop::PostTask", *pending_task);
 
   bool was_empty = incoming_queue_.empty();
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
-  if (always_schedule_work_ || (!message_loop_scheduled_ && was_empty)) {
+  if (message_loop_ &&
+      (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
     // Wake up the message loop.
     message_loop_->ScheduleWork();
     // After we've scheduled the message loop, we do not need to do so again
     // until we know it has processed all of the work in our queue and is
     // waiting for more work again. The message loop will always attempt to
     // reload from the incoming queue before waiting again so we clear this flag
     // in ReloadWorkQueue().
     message_loop_scheduled_ = true;
   }
 
   return true;
 }
 
 }  // namespace internal
 }  // namespace base