Make JingleThreadMessageLoop usable without JingleThread.

remoting/jingle_glue/jingle_thread.h

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
 #ifndef REMOTING_JINGLE_GLUE_JINGLE_THREAD_H_
 #define REMOTING_JINGLE_GLUE_JINGLE_THREAD_H_
 
 #include "base/message_loop.h"
 #include "base/tracked_objects.h"
 #include "base/synchronization/waitable_event.h"
 #include "third_party/libjingle/source/talk/base/messagequeue.h"
@@ skipping 12 matching lines @@
   TaskPump();
 
   // TaskRunner methods.
   virtual void WakeTasks();
   virtual int64 CurrentTime();
 
   // MessageHandler methods.
   virtual void OnMessage(talk_base::Message* pmsg);
 };
 
+class JingleThreadMessageLoop : public MessageLoop {

[Wez, 2011/07/01 20:33:00]

Isn't this really a Jingle-aware MessageLoop, so no need for Thread in the name?

[Sergey Ulanov, 2011/07/01 21:14:28]

It's a MessageLoop that runs tasks on a libjingle thread. JingleMessageLoop - is
very confusing. For example it may be interpreted as a MessageLoop that can run
libjingle tasks/messages.

[Wez, 2011/07/01 21:49:28]

OK, understood.

+ public:
+  JingleThreadMessageLoop(talk_base::Thread* thread);
+  virtual ~JingleThreadMessageLoop();
+
+  void Initialize();
+
+ private:
+  // AutoRunState sets |state_| for this message loop. It needs to be
+  // created here because we never call Run() or RunAllPending() for

[Wez, 2011/07/01 20:33:00]

nit: It's not being created here, this is just the definition of the member that
holds it.

AutoRunState is actually for use when nesting MessageLoop::Run() calls, to
ensure that only the top-most Run() is exited by Quit() calls made within it. 
It also seems to be an un-documented detail within MessageLoop, so I'm dubious
about using it, especially in this context.

Would it make more sense to call talk_base::Thread::Run() *through*
JingleThreadMessageLoop::Run()?  The latter Run call would then create the
JingleMessagePump, create the AutoRunState on the stack, and call Run() on the
pump with itself as the delegate; the pump would then call
talk_base::Thread::Run().

[Sergey Ulanov, 2011/07/01 21:14:28]

Moved the comment.
Yes, it's a bit hacky, but MessageLoop was never intended to be used in a ways
we use it here. We will be able to get rid of this code when we switch to using
chromium-based IO in the host.
Yes, we have something like this in jingle/glue/thread_wrapper.[h|cc]. This
class accomplishes the opposite task: it runs MessageLoop on a jingle thread.
The reason we need it is because we use libjingle-based IO (on host and in
tests) which works only on a thread that runs talk_base::Thread::Run(). If try
to use libjingle IO code on a regular chromium code it will not work because
there is no way it can get async IO notifications.

[Wez, 2011/07/01 21:49:28]

Yes, but what I'm suggesting is that since we are in control of the
JingleThread::Run(), we can have it create the MessageLoop & Run() it, then have
that Run() the MessagePump, and finally have the MessagePump call
talk_base::Thread::Run()?  That way jingle has the right kind of thread to run
on.

[Sergey Ulanov, 2011/07/01 22:40:54]

Done.

+  // the thread.
+  scoped_ptr<AutoRunState> jingle_message_loop_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(JingleThreadMessageLoop);
+};
+
 // TODO(sergeyu): This class should be changed to inherit from Chromiums
 // base::Thread instead of libjingle's thread.
 class JingleThread : public talk_base::Thread,
                      public talk_base::MessageHandler {
  public:
   JingleThread();
   virtual ~JingleThread();
 
   void Start();
 
   // Main function for the thread. Should not be called directly.
   virtual void Run();
 
   // Stop the thread.
   virtual void Stop();
 
   // Returns Chromiums message loop for this thread.
   // TODO(sergeyu): remove this method when we use base::Thread instead of
   // talk_base::Thread
   MessageLoop* message_loop();
 
   // Returns task pump if the thread is running, otherwise NULL is returned.
   TaskPump* task_pump();
 
  private:
-  class JingleMessageLoop;
-  class JingleMessagePump;
-
   virtual void OnMessage(talk_base::Message* msg);
 
   TaskPump* task_pump_;
   base::WaitableEvent started_event_;
   base::WaitableEvent stopped_event_;
   MessageLoop* message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(JingleThread);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_JINGLE_GLUE_JINGLE_THREAD_H_