dbus: allow unregistering of exported objects

dbus/bus.h

Index: dbus/bus.h
diff --git a/dbus/bus.h b/dbus/bus.h
index 2684dcd0235f1982ae90e7ee90f72668c5dc0eba..10a3dfe11c128ee3657e90d30c3fdd05038135d8 100644
--- a/dbus/bus.h
+++ b/dbus/bus.h
@@ -226,6 +226,15 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
   // Must be called in the origin thread.
   virtual ExportedObject* GetExportedObject(const ObjectPath& object_path);
 
+  // Unregisters the exported object for the given object path |object_path|.
+  //
+  // Getting an exported object for the same object path after this call
+  // will return a new object, method calls on any remaining copies of the
+  // previous object will not be called.
+  //
+  // BLOCKING CALL. Must be called in the origin thread.

[satorux1, 2012/03/13 18:27:25]

On what thread this function is called? For instance, we shouldn't block the UI
thread.

[keybuk, 2012/03/13 18:32:41]

probably the UI thread ... alternate suggestions welcome

[satorux1, 2012/03/13 18:42:01]

maybe:

1) add a callback parameter to UnregisterExportedObject, and let
BluetoothAgentServiceProviderImpl use it properly, before the destructor is
called. would it be difficult?

2) rather than block in UnregisterExportedObject, block in
Bus::ShutdownAndBlockOnDBusThreadInternal? we can probably do this by
dbus_thread_message_loop_->RunAllPendings()

[keybuk, 2012/03/13 18:53:31]

1) there's no place to call because the destructor is called as a result of the
scoped_ptr<> freeing the contained object - there isn't a sensible shutdown path
here

2) this isn't shutdown, this is unregistering an object without shutting down
the bus

[satorux1, 2012/03/13 18:56:36]

re 2, i meant to just post tasks to d-bus thread from
UnregisterExportedObject(), and make sure all of these tasks
were run at the shutdown time.

+  virtual void UnregisterExportedObject(const ObjectPath& object_path);
+
   // Shuts down the bus and blocks until it's done. More specifically, this
   // function does the following:
   //
@@ -420,6 +429,11 @@ class Bus : public base::RefCountedThreadSafe<Bus> {
  private:
   friend class base::RefCountedThreadSafe<Bus>;
 
+  // Helper function used for UnregisterExportedObject(), |completion| is
+  // the waitable event that allows the caller to block until complete.
+  void UnregisterExportedObjectInternal(const ObjectPath& object_path,
+                                        base::WaitableEvent* completion);
+
   // Helper function used for ShutdownOnDBusThreadAndBlock().
   void ShutdownOnDBusThreadAndBlockInternal();