Add a method to check if a D-Bus service has an owner. Use it for mtpd.

dbus/bus.h

Index: dbus/bus.h
===================================================================
--- dbus/bus.h	(revision 197157)
+++ dbus/bus.h	(working copy)
@@ -211,6 +211,12 @@
   // - the requested service name.
   // - whether ownership has been obtained or not.
   typedef base::Callback<void (const std::string&, bool)> OnOwnershipCallback;
+
+  // Called when GetServiceOwner() completes.
+  // |service_owner| is the return value from GetServiceOwnerAndBlock().
+  typedef base::Callback<void (const std::string& service_owner)>
+      GetServiceOwnerCallback;
+
   // TODO(satorux): Remove the service name parameter as the caller of
   // RequestOwnership() knows the service name.
 
@@ -530,6 +536,19 @@
   // AssertOnOriginThread().
   virtual void AssertOnDBusThread();
 
+  // Gets the owner for |service_name| via org.freedesktop.DBus.GetNameOwner.
+  // Returns the owner name, if any, or an empty string on failure.
+  // Set |suppress_errors| to true to avoid printing error messages.
+  //
+  // BLOCKING CALL.
+  virtual std::string GetServiceOwnerAndBlock(const std::string& service_name,

[satorux1, 2013/04/30 04:50:00]

Seems to me that we we don't need to expose the blocking version. Please move
this to private: section.

[Lei Zhang, 2013/04/30 20:49:23]

Used in object_proxy.cc.

+                                              bool suppress_errors);

[satorux1, 2013/04/30 04:50:00]

so far, this is always true, right? please remove this parameter.

[Lei Zhang, 2013/04/30 20:49:23]

It's false in object_proxy.cc.

[satorux1, 2013/05/01 01:19:27]

I see. Then could you make it an enum as boolean is hard to read in client code
(ex. false of what?) like

enum GetServiceOwnerOption {
  REPORT_ERRORS,
  SUPPRESS_ERRORS,
}

[Lei Zhang, 2013/05/01 01:40:50]

Done.

+
+  // A non-blocking version of GetServiceOwnerAndBlock().
+  // Must be called in the origin thread.
+  virtual void GetServiceOwner(const std::string& service_name,
+                               const GetServiceOwnerCallback& callback);
+
   // Returns true if the bus is connected to D-Bus.
   bool is_connected() { return connection_ != NULL; }
 
@@ -555,6 +574,10 @@
   void RequestOwnershipInternal(const std::string& service_name,
                                 OnOwnershipCallback on_ownership_callback);
 
+  // Helper function used for GetServiceOwner().
+  void GetServiceOwnerInternal(const std::string& service_name,
+                               const GetServiceOwnerCallback& callback);
+
   // Processes the all incoming data to the connection, if any.
   //
   // BLOCKING CALL.