Lazily initialize MessageLoop for faster thread startup

base/message_loop/message_loop_proxy_impl.cc

 // Copyright (c) 2012 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/message_loop_proxy_impl.h"
 
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/message_loop/incoming_task_queue.h"
 #include "base/message_loop/message_loop.h"
 
 namespace base {
 namespace internal {
 
-MessageLoopProxyImpl::MessageLoopProxyImpl(
-    scoped_refptr<IncomingTaskQueue> incoming_queue)
-    : incoming_queue_(incoming_queue),
-      valid_thread_id_(PlatformThread::CurrentId()) {
+// static
+MessageLoopProxyImpl* MessageLoopProxyImpl::Create(
+    scoped_refptr<IncomingTaskQueue> incoming_queue) {
+  return new MessageLoopProxyImpl(incoming_queue, false /* lazy_init */);
+}
+
+// static
+MessageLoopProxyImpl* MessageLoopProxyImpl::CreateForLazyInit(
+    scoped_refptr<IncomingTaskQueue> incoming_queue) {
+  return new MessageLoopProxyImpl(incoming_queue, true /* lazy_init */);
 }
 
 bool MessageLoopProxyImpl::PostDelayedTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task,
     base::TimeDelta delay) {
   DCHECK(!task.is_null()) << from_here.ToString();
   return incoming_queue_->AddToIncomingQueue(from_here, task, delay, true);
 }
 
 bool MessageLoopProxyImpl::PostNonNestableDelayedTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task,
     base::TimeDelta delay) {
   DCHECK(!task.is_null()) << from_here.ToString();
   return incoming_queue_->AddToIncomingQueue(from_here, task, delay, false);
 }
 
 bool MessageLoopProxyImpl::RunsTasksOnCurrentThread() const {
   return valid_thread_id_ == PlatformThread::CurrentId();
 }
 
+void MessageLoopProxyImpl::LazyInit() {
+  DCHECK_EQ(kInvalidThreadId, valid_thread_id_);
+  valid_thread_id_ = PlatformThread::CurrentId();
+}
+
+MessageLoopProxyImpl::MessageLoopProxyImpl(
+    scoped_refptr<IncomingTaskQueue> incoming_queue,
+    bool lazy_init)

[rvargas (doing something else), 2015/03/26 02:19:27]

Maybe it's better to remove this argument and set valid_thread_id_ from the
factory method (if called from the proxied thread)

[kinuko, 2015/04/13 02:02:59]

Removed.

+    : incoming_queue_(incoming_queue),
+      valid_thread_id_(lazy_init ? kInvalidThreadId
+                                 : PlatformThread::CurrentId()) {
+}
+
 MessageLoopProxyImpl::~MessageLoopProxyImpl() {
 }
 
 }  // namespace internal
 
 scoped_refptr<MessageLoopProxy>
 MessageLoopProxy::current() {
   MessageLoop* cur_loop = MessageLoop::current();
   if (!cur_loop)
     return NULL;
   return cur_loop->message_loop_proxy();
 }
 
 }  // namespace base