Lazily initialize MessageLoop for faster thread startup

base/threading/thread.cc

Index: base/threading/thread.cc
diff --git a/base/threading/thread.cc b/base/threading/thread.cc
index ea5b1747e3836a8092517b19e8197d1cf3debb62..6e7dcfa86ac1b828b352172c287dcf848dd53148 100644
--- a/base/threading/thread.cc
+++ b/base/threading/thread.cc
@@ -36,20 +36,6 @@ void ThreadQuitHelper() {
   Thread::SetThreadWasQuitProperly(true);
 }
 
-// Used to pass data to ThreadMain.  This structure is allocated on the stack
-// from within StartWithOptions.
-struct Thread::StartupData {
-  // We get away with a const reference here because of how we are allocated.
-  const Thread::Options& options;
-
-  // Used to synchronize thread startup.
-  WaitableEvent event;
-
-  explicit StartupData(const Options& opt)
-      : options(opt),
-        event(false, false) {}
-};
-
 Thread::Options::Options()
     : message_loop_type(MessageLoop::TYPE_DEFAULT),
       timer_slack(TIMER_SLACK_NONE),
@@ -71,13 +57,10 @@ Thread::Thread(const std::string& name)
 #if defined(OS_WIN)
       com_status_(NONE),
 #endif
-      started_(false),
       stopping_(false),
       running_(false),
-      startup_data_(NULL),
       thread_(0),
-      message_loop_(NULL),
-      thread_id_(kInvalidThreadId),
+      message_loop_(nullptr),
       name_(name) {
 }
 
@@ -108,34 +91,49 @@ bool Thread::StartWithOptions(const Options& options) {
 
   SetThreadWasQuitProperly(false);
 
-  StartupData startup_data(options);
-  startup_data_ = &startup_data;
+  scoped_ptr<MessageLoop::LazyInitOptions> message_loop_options(
+      new MessageLoop::LazyInitOptions);
+  message_loop_options->message_loop_type = options.message_loop_type;
+  message_loop_options->message_pump_factory = options.message_pump_factory;
+  message_loop_options->timer_slack = options.timer_slack;
+  message_loop_ = MessageLoop::CreateForLazyInit(message_loop_options.Pass());
+
+  start_event_.reset(new WaitableEvent(false, false));
 
   if (!PlatformThread::Create(options.stack_size, this, &thread_)) {
     DLOG(ERROR) << "failed to create thread";
-    startup_data_ = NULL;
+    delete message_loop_;
+    message_loop_ = NULL;
+    start_event_.reset();
     return false;
   }
 
-  // TODO(eroman): Remove once crbug.com/465458 is solved.
-  tracked_objects::ScopedTracker tracking_profile_wait(
-      FROM_HERE_WITH_EXPLICIT_FUNCTION(
-          "465458 base::Thread::StartWithOptions (Wait)"));
-
-  // Wait for the thread to start and initialize message_loop_
-  base::ThreadRestrictions::ScopedAllowWait allow_wait;
-  startup_data.event.Wait();
+  DCHECK(message_loop_);
+  return true;
+}
 
-  // set it to NULL so we don't keep a pointer to some object on the stack.
-  startup_data_ = NULL;
-  started_ = true;
+bool Thread::StartAndWait() {
+  bool result = Start();
+  if (!result)
+    return result;
+  WaitUntilThreadStarted();
+  return result;
+}
 
-  DCHECK(message_loop_);
+bool Thread::WaitUntilThreadStarted() {
+  if (!start_event_)
+    return false;
+  // TODO(kinuko): Remove once crbug.com/465458 is solved.
+  tracked_objects::ScopedTracker tracking_profile(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+        "465458 base::Thread::WaitUntilThreadStarted()"));
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
+  start_event_->Wait();
   return true;
 }
 
 void Thread::Stop() {
-  if (!started_)
+  if (!start_event_)
     return;
 
   StopSoon();
@@ -151,7 +149,7 @@ void Thread::Stop() {
   DCHECK(!message_loop_);
 
   // The thread no longer needs to be joined.
-  started_ = false;
+  start_event_.reset();
 
   stopping_ = false;
 }
@@ -159,9 +157,7 @@ void Thread::Stop() {
 void Thread::StopSoon() {
   // We should only be called on the same thread that started us.
 
-  // Reading thread_id_ without a lock can lead to a benign data race
-  // with ThreadMain, so we annotate it to stay silent under ThreadSanitizer.
-  DCHECK_NE(ANNOTATE_UNPROTECTED_READ(thread_id_), PlatformThread::CurrentId());
+  DCHECK_NE(thread_id(), PlatformThread::CurrentId());
 
   if (stopping_ || !message_loop_)
     return;
@@ -171,13 +167,15 @@ void Thread::StopSoon() {
 }
 
 bool Thread::IsRunning() const {
-  return running_;
+  if (stopping_)

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

Now I see... there's a giant lock in Stop (Join), can we just use the event
without stopping_ and lock_?. I presume a test complained.

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

Not only for testing but also in production code (e.g.
PrintJob::ControlledWorkerShutdown()) this behavior seems to be expected.  We
can probably change the callsite code but I'd like to keep the existing behavior
during the refactoring.

+    return IsInRunLoop();
+  return !!start_event_;
 }
 
 void Thread::SetPriority(ThreadPriority priority) {
   // The thread must be started (and id known) for this to be
   // compatible with all platforms.
-  DCHECK_NE(thread_id_, kInvalidThreadId);
+  DCHECK(!!start_event_);

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

nit: shouldn't need !! (scoped_ptr is testable)

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

Done.

   PlatformThread::SetThreadPriority(thread_, priority);
 }
 
@@ -199,24 +197,16 @@ bool Thread::GetThreadWasQuitProperly() {
 
 void Thread::ThreadMain() {
   {

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

nit: remove this

[kinuko, 2015/04/13 02:03:00]

Done.

-    // The message loop for this thread.
-    // Allocated on the heap to centralize any leak reports at this line.
-    scoped_ptr<MessageLoop> message_loop;
-    if (!startup_data_->options.message_pump_factory.is_null()) {
-      message_loop.reset(
-          new MessageLoop(startup_data_->options.message_pump_factory.Run()));
-    } else {
-      message_loop.reset(
-          new MessageLoop(startup_data_->options.message_loop_type));
-    }
-
     // Complete the initialization of our Thread object.
-    thread_id_ = PlatformThread::CurrentId();
+    DCHECK_EQ(thread_id(), PlatformThread::CurrentId());
     PlatformThread::SetName(name_.c_str());
     ANNOTATE_THREAD_NAME(name_.c_str());  // Tell the name to race detector.
-    message_loop->set_thread_name(name_);
-    message_loop->SetTimerSlack(startup_data_->options.timer_slack);
-    message_loop_ = message_loop.get();
+
+    // Lazily initialize the message_loop so that it can run on this thread.
+    DCHECK(message_loop_);
+    scoped_ptr<MessageLoop> message_loop(message_loop_);

[rvargas (doing something else), 2015/03/26 02:19:28]

Is this intentional?

[kinuko, 2015/04/13 02:03:00]

Sort of. (This needs to be freed at the end of main)

+    message_loop_->set_thread_name(name_);
+    message_loop_->LazyInit();
 
 #if defined(OS_WIN)
     scoped_ptr<win::ScopedCOMInitializer> com_initializer;
@@ -228,16 +218,21 @@ void Thread::ThreadMain() {
 #endif
 
     // Let the thread do extra initialization.
-    // Let's do this before signaling we are started.
     Init();
 
-    running_ = true;
-    startup_data_->event.Signal();
-    // startup_data_ can't be touched anymore since the starting thread is now
-    // unlocked.
+    {
+      AutoLock lock(lock_);
+      running_ = true;
+    }
+
+    start_event_->Signal();
 
     Run(message_loop_);
-    running_ = false;
+
+    {
+      AutoLock lock(lock_);
+      running_ = false;
+    }
 
     // Let the thread do extra cleanup.
     CleanUp();
@@ -254,4 +249,9 @@ void Thread::ThreadMain() {
   }
 }
 
+bool Thread::IsInRunLoop() const {
+  base::AutoLock lock(lock_);
+  return running_;
+}
+
 }  // namespace base