Lazily initialize MessageLoop for faster thread startup

base/message_loop/message_loop_proxy_impl.cc

Index: base/message_loop/message_loop_proxy_impl.cc
diff --git a/base/message_loop/message_loop_proxy_impl.cc b/base/message_loop/message_loop_proxy_impl.cc
index b7abca377e668270d2f1db89f54c3731de577602..1a54ddad00bb0c1f9c554c43c913ac24a32cf561 100644
--- a/base/message_loop/message_loop_proxy_impl.cc
+++ b/base/message_loop/message_loop_proxy_impl.cc
@@ -12,10 +12,16 @@
 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(
@@ -38,6 +44,19 @@ 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() {
 }