Synchronously sends message to the peer represented by this and blocks the calling thread 
            until a reply is received or the timeout is reached.
See send_message_with_reply for the asynchronous version of this method.
Unless flags contain the g_dbus_send_message_flags_preserve_serial flag, the 
            serial number will be assigned by this and set on message via 
            set_serial. If out_serial is not 
            null, then the serial number used will be written to this location prior to submitting the 
            message to the underlying transport.
If this is closed then the operation will fail with 
              g_io_error_closed. If cancellable is canceled, the operation will fail with 
              g_io_error_cancelled. If message is not well-formed, the operation fails with 
              g_io_error_invalid_argument.
Note that throws is only set if a local in-process error occurred. That is to say that the returned DBusMessage object may be of type g_dbus_message_type_error. Use to_gerror to transcode this to a Error.
See this server and client for an example of how to use this low-level API to send and receive UNIX file descriptors.
Note that message must be unlocked, unless flags contain the 
              g_dbus_send_message_flags_preserve_serial flag.
| this | |
| message | |
| flags | flags affecting how the message is sent. | 
| timeout_msec | the timeout in milliseconds, -1 to use the default timeout or g_maxint for no timeout | 
| out_serial | return location for serial number  assigned to  | 
| cancellable | a Cancellable or null | 
| a locked DBusMessage that is the reply  to  |