Lazily initialize MessageLoop for faster thread startup

base/message_loop/incoming_task_queue.cc

Index: base/message_loop/incoming_task_queue.cc
diff --git a/base/message_loop/incoming_task_queue.cc b/base/message_loop/incoming_task_queue.cc
index c1ce939b0c4708ac431d80b54a35ee8ef73b314c..067cbb1bf5e984329a953adc29a5f1b80e542b52 100644
--- a/base/message_loop/incoming_task_queue.cc
+++ b/base/message_loop/incoming_task_queue.cc
@@ -109,6 +109,21 @@ void IncomingTaskQueue::WillDestroyCurrentMessageLoop() {
   message_loop_ = NULL;
 }
 
+void IncomingTaskQueue::StartScheduling() {
+  AutoLock lock(incoming_queue_lock_);
+  DCHECK(!is_ready_for_scheduling_);

[Nico, 2015/04/24 21:31:15]

DCHECK(!message_loop_scheduled_) (…right?)

[kinuko, 2015/04/27 16:36:04]

Done.

+  is_ready_for_scheduling_ = true;

[danakj, 2015/04/24 20:54:39]

Can you DCHECK !message_loop_scheduled_ here?

[kinuko, 2015/04/27 16:36:04]

Done.

+  if (!incoming_queue_.empty()) {
+    message_loop_->ScheduleWork();
+    message_loop_scheduled_ = true;
+  }
+}
+
+bool IncomingTaskQueue::empty() {
+  AutoLock lock(incoming_queue_lock_);
+  return incoming_queue_.empty();
+}
+
 IncomingTaskQueue::~IncomingTaskQueue() {
   // Verify that WillDestroyCurrentMessageLoop() has been called.
   DCHECK(!message_loop_);
@@ -148,7 +163,8 @@ bool IncomingTaskQueue::PostPendingTask(PendingTask* pending_task) {
   incoming_queue_.push(*pending_task);
   pending_task->task.Reset();
 
-  if (always_schedule_work_ || (!message_loop_scheduled_ && was_empty)) {
+  if (is_ready_for_scheduling_ &&
+      (always_schedule_work_ || (!message_loop_scheduled_ && was_empty))) {
     // Wake up the message loop.

[danakj, 2015/04/24 20:54:39]

Can you break this into a helper method so you can share the code (and more
especially the comments)?

[kinuko, 2015/04/27 16:36:04]

Done.

     message_loop_->ScheduleWork();
     // After we've scheduled the message loop, we do not need to do so again