Receiving signals the easy way?

[Kees Jongenburger]

Hi

I am trying to receive a signal in my dbus-glib based program. I found
a good example on the net to listen to dbus signals itself but am
currently failing
to implement it for my own purposes.

the code looks pretty much like this (the real code can be fetched from
( http://github.com/keesj/dbus_glib_pthread/raw/master/notification_test.c )


/* get a system bus
  create a proxy object
  register a known signal called Notify with no parameters
  register a callback
   runt the main loop */

connection = dbus_g_bus_get(DBUS_BUS_SYSTEM, &error);
proxy = dbus_g_proxy_new_for_name(connection,  "com.test.Notification",
                                          "/com/test/Notification",
"com.test.Notification");
dbus_g_proxy_add_signal(proxy, "Notify",G_TYPE_INVALID);
dbus_g_proxy_connect_signal(proxy, "Notify", test_callback, NULL, NULL);

=================

After that I call
dbus-send \
        --system \
        /com/test/Notification \
        com.test.Notification.Notify
but don't receive anything in my callback so I must be missing something.

I implemented the same signal listener in java
(http://github.com/keesj/dbus_glib_pthread/java) and that one works
like a charm. This leave me with the following questions
1) what am I doing wrong?
2) in this situation there is no object registered on the bus called
Notification, who owns the signal interface?
3) Is there any form of security that I might be missing (can
everybody send signals to everybody and can everybody listen?)

Greetings
_______________________________________________
dbus mailing list
dbus@...
http://lists.freedesktop.org/mailman/listinfo/dbus

[Will Thompson-5]

On 01/11/09 12:38, Kees Jongenburger wrote:
> proxy = dbus_g_proxy_new_for_name(connection,  "com.test.Notification",
>                                           "/com/test/Notification",
> "com.test.Notification");

You've constructed a proxy for an object on the bus name
"com.test.Notification"...

> dbus_g_proxy_add_signal(proxy, "Notify",G_TYPE_INVALID);
> dbus_g_proxy_connect_signal(proxy, "Notify", test_callback, NULL, NULL);

and bound to the Notify signal. Then:

> dbus-send \
>         --system \
>         /com/test/Notification \
>         com.test.Notification.Notify

a service connects to the bus, receives a unique name like :1.23, and
emits the com.test.Notification.Notify signal from its
/com/test/Notification object. But you bound to signal emissions by
com.test.Notification, not :1.23.

--
Will
_______________________________________________
dbus mailing list
dbus@...
http://lists.freedesktop.org/mailman/listinfo/dbus

[Kees Jongenburger]

Hi Will

On Sun, Nov 1, 2009 at 1:44 PM, Will Thompson
<will.thompson@...> wrote:

> On 01/11/09 12:38, Kees Jongenburger wrote:
>> dbus-send \
>>         --system \
>>         /com/test/Notification \
>>         com.test.Notification.Notify
>
> a service connects to the bus, receives a unique name like :1.23, and
> emits the com.test.Notification.Notify signal from its
> /com/test/Notification object. But you bound to signal emissions by
> com.test.Notification, not :1.23.

Thanks for clarifying what is happening. I am apparently trying to use
signals to broadcast changes. This doesn't work
because signals are "sent" from object and not fired at.

Part of what I am trying to achieve is for a UI to be aware of what is
happening downstairs and part of that design is that I don't want the
lower processes to call upon a interface of a higher layer.

on IRC Will suggested the following and I think this might be the
proper way of doing this:

Make all the processes take a name of the form
com.your.domain.Service.* for some *. And have the UI watch
NameOwnerChanged for people taking such names. Then make each service
have an object /com/your/domain/Service/Foo implementing the
com.your.domain.Service interface, with a signal that the UI listens
to

pseudo code:
def name_owner_changed_cb( name, old owner, new owner):
     if name.starts_with("com.your.domain.Service.") and new_owner != "":
         proxy = ProxyObject(name=name, path=("/" +
name.replace_all(".", "/")), interface="com.your.domain.Service")
         proxy.connect_to_signal("Notify", notify_cb)
 and in the "foo" service:
 def main():
     connect to the bus
     bus.RequestName("com.your.domain.Service.foo")

For the moment I went for a different approach (less code) and I am
possibly misusing signals. I used, thanks for WIll's hint, a lower
level API to allow myself to register a dbus match rule.

so I copied the code from here
http://www.ibm.com/developerworks/linux/library/l-dbus.html and
modified it to
http://github.com/keesj/dbus_glib_pthread/raw/master/notification_test2.c

Thanks for the help!
_______________________________________________
dbus mailing list
dbus@...
http://lists.freedesktop.org/mailman/listinfo/dbus