maemo.org - Talk - Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

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Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Hi, developers...
I'd like to enhance Queen Beecon Widget with the ability to perform QBW to QBW instance and System to QBW instance IPC (Inter Process Communication).

I just need a very basic and simple IPC mechanism which responds to commands like these:

Code:

run-standalone.sh dbus-send --session --type=signal /com/nokia/qbw/Object com.nokia.qbw.Interface.update string:"id0" string:"layout"

Code:

run-standalone.sh dbus-send --session --type=signal /com/nokia/qbw/Object com.nokia.qbw.Interface.update string:"id<xx>" string:"content"

and let QBW instance (id0 ... id<xx>) perform relevant actions (update QBW layout or update QBW content or ...)

I already coded some snippets into QBW:

DBUS, Signal & Marshalling includes:

PHP Code:


		
			
...
#include <dbus/dbus-glib.h>
...
#include <signal.h>
...
#include <marshal.h>

Signal Callback declaration:

PHP Code:


		
			
static void queen_beecon_handle_dbus_signal_update (const DBusGProxy *object G_GNUC_UNUSED, const gchar *id, const gchar *status G_GNUC_UNUSED, const QueenBeecon *self);

Constants declarations:

PHP Code:


		
			
/* libcsnet D-Bus definitions */
#define QBW_DBUS_SERVICE  "com.nokia.qbw.Service"
#define QBW_DBUS_PATH  "/com/nokia/qbw/Object"
#define QBW_DBUS_IFACE "com.nokia.qbw.Interface"

#define QBW_UPDATE_SIGNAL            "update"
#define QBW_UPDATE_SIGNAL_LAYOUT    "layout"
#define QBW_UPDATE_SIGNAL_CONTENT    "content"

Global DBUS Connection and Proxy definitions:

PHP Code:


		
			
static DBusGConnection    *dbus_conn=NULL;
static DBusGProxy        *qbw_proxy=NULL;

Private class instance ID definition for signals:

PHP Code:


		
			
struct _QueenBeeconPrivate
{
        ...

        // DBUS Signal
        gchar             *qbwSigId;
};

Signal callback function definition:

PHP Code:


		
			
static void queen_beecon_handle_dbus_signal_update (const DBusGProxy *object G_GNUC_UNUSED, const gchar *id, const gchar *action, const QueenBeecon *self)
{
    g_warning ("(%p) queen_beecon_handle_dbus_signal (id=%s, action=%s)",self, id, action);

    if (g_strcmp0(id,self->priv->qbwSigId)) return; //if signal is not for current instance .... return

    if (!g_strcmp0(action, QBW_UPDATE_SIGNAL_LAYOUT))
        queen_beecon_update_content_layout ((QueenBeecon *)self); // No... only update layout
    else
        queen_beecon_update_content ((QueenBeecon *)self);
}

Signal connection at instance initialization:

PHP Code:


		
			
static void queen_beecon_realize (GtkWidget *widget)
{
g_warning ("(%p) queen_beecon_realize",widget);
    QueenBeecon *self = QUEEN_BEECON (widget);
    ...
    self->priv->qbwSigId = NULL;
    self->priv->qbwSigId = g_strdup_printf("id%s",&last_dot[1]);
    dbus_g_proxy_connect_signal (qbw_proxy, QBW_UPDATE_SIGNAL, G_CALLBACK (queen_beecon_handle_dbus_signal_update), self, NULL);
}

Signal disconnection at instance termination:

PHP Code:


		
			
static void queen_beecon_finalize (GObject *object)
{
g_warning ("(%p) queen_beecon_finalize",object);
    QueenBeecon *self = QUEEN_BEECON (object);

    ...
    dbus_g_proxy_disconnect_signal (qbw_proxy, QBW_UPDATE_SIGNAL, G_CALLBACK (queen_beecon_handle_dbus_signal_update), self);

DBUS connection and Proxy creation at QBW main class instantiation:

PHP Code:


		
			
static void queen_beecon_class_init (QueenBeeconClass *klass)
{
g_warning ("(%p) queen_beecon_class_init",klass);
    ...
    GError* error = NULL;
    DBusGProxy *remote_object;

    dbus_conn = dbus_g_bus_get(DBUS_BUS_SESSION, &error);
    if (error != NULL) {
        ...
      }

    qbw_proxy = dbus_g_proxy_new_for_name (dbus_conn, QBW_DBUS_SERVICE, QBW_DBUS_PATH, QBW_DBUS_IFACE);

    if (G_LIKELY (qbw_proxy))    {
        dbus_g_object_register_marshaller (marshal_VOID__STRING_STRING, G_TYPE_NONE, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_INVALID);
        dbus_g_proxy_add_signal (qbw_proxy, QBW_UPDATE_SIGNAL, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_INVALID);
    }
    dbus_g_connection_flush (dbus_conn);
    ...
}

Signal disconnection and DBUS unreferencing when last QBW instance closed and class dismissed:

PHP Code:


		
			
static void queen_beecon_class_finalize (QueenBeeconClass *klass G_GNUC_UNUSED)
{
    ...
    if (qbw_proxy) {
        g_object_unref (qbw_proxy);
    }

    if (dbus_conn) dbus_g_connection_unref (dbus_conn);
}

To test my code, I issue dbus-send commands:

Code:

[sbox-FREMANTLE_X86: ~] > run-standalone.sh dbus-send --session --type=signal /com/nokia/qbw/Object com.nokia.qbw.Interface.update string:"id0" string:"layout"

[sbox-FREMANTLE_X86: ~] > run-standalone.sh dbus-send --session --type=signal /com/nokia/qbw/Object com.nokia.qbw.Interface.update string:"id0" string:"xxx"

[sbox-FREMANTLE_X86: ~] >

dbus-monitor reports signals on the bus:

Code:

[sbox-FREMANTLE_X86: ~] >  run-standalone.sh dbus-monitor "type='signal',interface='com.nokia.qbw.Interface'"

signal sender=org.freedesktop.DBus -> dest=:1.35 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired

   string ":1.35"

signal sender=:1.36 -> dest=(null destination) serial=2 path=/com/nokia/qbw/Object; interface=com.nokia.qbw.Interface; member=update

   string "id0"

   string "layout"

signal sender=:1.37 -> dest=(null destination) serial=2 path=/com/nokia/qbw/Object; interface=com.nokia.qbw.Interface; member=update

   string "id0"

   string "xxx"

but QBW is unable to receive any signal at all, thus not triggering callback functions to perform requested actions.

Any help will be greately appreciated.

I already googled here and there for hints but without success.
Also I already had a look at Help with creating daemon for n900 thread here
Ciao.

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Hello,

I'm no D-Bus expert, but I don't think signals are what you want. Signals, generally, are emitted when your application does something and you want listeners to be notified of a change. A method call would be better suited to this application.

Anyway, what you appear to be doing would be listening for a signal emission. I guess you'd specify that it is your program providing the method call.

The DBus-GLib way would be http://dbus.freedesktop.org/doc/dbus...ml#glib-server

Examples of programs doing this are, off the top of my head: Evince (look for its XML files), Diablo's hildon-desktop (look in the background-manager folder), my FMTX Faker (I would not recommend looking at it, however) and N900 FMRX Enabler among others.

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by qwerty12 (Post 656759)

Xx for really quick response ...

I know signals is not the most orthodox way to do that and methods are the way to go ... I just needed a quick, cheap and dirty solution to provide very basic IPC.

For use case and very simple POC: imagine 1 QBW (button) which gives "roll" impulse to 2 instances of QBW Naive Dice Roller, or drives "shuffle" of - say - 5 cards-looking QBWs or (long requested) have many QBW buttons for changing CPU overclocking frequencies and impulse to a gauge QBW for displaying results and other stats.

I'll inspect much further but it's still a mistery why QBW doesn't receive signals (I tried also with a basic signal with no parameters and no marshalling)

Second mistery is how I can debug issues like this one...

Ciao.

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

My attempt is attached. It's pretty bad and I'm not sure all instances recieve the signal...

Test with "dbus-send --session --type=method_call --dest=com.nokia.qbw /com/nokia/qbw com.nokia.qbw.update string:"id0" string:"layout""

Crap, I forgot to apply the org.freedesktop.DBus.GLib.NoReply attribute

OK, it does only work for one instance. What you probably should do is when dbus-g-connection-register-g-object is called, is to append the path "/com/nokia/qbw" so that it looks like "/com/nokia/qbw/$ID" so that each instance of the object has their own path - this way you also don't need to pass the id as a parameter too

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by qwerty12 (Post 657284)

Can't see the "SUPER-MEGA-HYPER-THANKS" button!!!
R E S P E C T... my friend!

I'll give it a shot tomorrow!!! :D

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Also remember that you're trying to use D-Bus not in an app, but in a hildon-desktop widget. Therefore, you need a special way to get hold of the DBusConnection.
An alternate hackish python way can be found in my recaller sourcecode (I'm using it for the autorecording, listening to systemdbus).

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by twaelti (Post 657402)

Yes, you are right ... I was aware of those special functions/stubs for hd_home_plugin_item* DBUS acquisition:

PHP Code:


		
			
/**

* hd_home_plugin_item_get_dbus_connection:

* @item: A #HDHomePluginItem

* @type: The #DBusBusType %DBUS_BUS_SESSION or %DBUS_BUS_SYSTEM

* @error: A #DBusError to return error messages

*

* Creates a new private #DBusConnection to the D-Bus session or system bus.

*

* It is similar to the dbus_bus_get_private() function but in contrast to the

* dbus_bus_get_private() function the application will not exit if the connection

* closes. Additionally this function is used to map the unique D-Bus name to the

* plugin.

*

* So this function should be used by plugins to create D-Bus connections.

*

* Returns: A new private connection to bus %type. The connection must be unrefed with

* dbus_connection_unref() when it is not longer needed.

**/

DBusConnection *

hd_home_plugin_item_get_dbus_connection (HDHomePluginItem *item,

DBusBusType type,

DBusError *error)

{

HDHomePluginItemPrivate *priv;

DBusConnection *connection;



g_return_val_if_fail (HD_IS_HOME_PLUGIN_ITEM (item), NULL);



priv = item->priv;



/* Create a private connection */

connection = dbus_bus_get_private (type, error);



if (!connection || (error != NULL && dbus_error_is_set (error)))

return NULL;



/* Do not exit on disconnect */

dbus_connection_set_exit_on_disconnect (connection, FALSE);



/* Log the connection name for debug purposes */

g_debug ("Plugin '%s' opened D-Bus connection '%s'.",

hd_home_plugin_item_get_dl_filename (item),

dbus_bus_get_unique_name (connection));



return connection;

}



/**

* hd_home_plugin_item_get_dbus_g_connection:

* @item: A #HDHomePluginItem

* @type: The #DBusBusType %DBUS_BUS_SESSION or %DBUS_BUS_SYSTEM

* @error: A #GError to return error messages

*

* Creates a new #DBusGConnection to the D-Bus session or system bus.

*

* Internally, calls dbus_g_bus_get(). See there for further informations.

*

* Returns: A shared connection.

**/

DBusGConnection *

hd_home_plugin_item_get_dbus_g_connection (HDHomePluginItem *item,

DBusBusType type,

GError **error)

{

HDHomePluginItemPrivate *priv;

DBusGConnection *g_connection;

DBusConnection *connection;

GError *tmp_error = NULL;



g_return_val_if_fail (HD_IS_HOME_PLUGIN_ITEM (item), NULL);



priv = item->priv;



/* Create a DBusGConnection (not private yet) */

g_connection = dbus_g_bus_get (type, &tmp_error);



if (tmp_error != NULL)

{

g_propagate_error (error, tmp_error);

return NULL;

}



connection = dbus_g_connection_get_connection (g_connection);



/* Log the connection name for debug purposes */

g_debug ("Plugin '%s' opened D-Bus connection '%s'.",

hd_home_plugin_item_get_dl_filename (item),

dbus_bus_get_unique_name (connection));



return g_connection;

}

but first time i tried I got and "assertion failed" notification stating that caller was not a hd_home_plugin_item.
However that could have been my mistake in calling the function back in my "try-this-and-see-what-happens" hours!!!

GOD SAVE THE MAEMO COMMUNITY!!!!
:cool:

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by qwerty12 (Post 657284)

...
Crap, I forgot to apply the org.freedesktop.DBus.GLib.NoReply attribute

Sorry ... not sure what to change for this ... could you please elaborate 2/3 lines more?

Quote:

Originally Posted by qwerty12 (Post 657284)

...
OK, it does only work for one instance. What you probably should do is when dbus-g-connection-register-g-object is called, is to append the path "/com/nokia/qbw" so that it looks like "/com/nokia/qbw/$ID" so that each instance of the object has their own path - this way you also don't need to pass the id as a parameter too

Yeah... that was one of my first concerns which ended up that way (string:id<xx>) because of the signal issues. But I agree "/com/nokia/qbw/$ID" is the way to go for multi-instance awareness.

Secondly got your warning here:

PHP Code:


		
			
#You are discouraged from using "com.nokia"!

QBW_DBUS_SERVICE="com.nokia.qbw"

AC_DEFINE_UNQUOTED(QBW_DBUS_SERVICE, "$QBW_DBUS_SERVICE", [Name of D-Bus service])

AC_SUBST([QBW_DBUS_SERVICE])

Could you suggest any other "safe" "not-well-known" name to use here?

Ciao.

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by No!No!No!Yes! (Post 657532)

Sorry ... not sure what to change for this ... could you please elaborate 2/3 lines more?

Sorry, please ignore me - that attribute is only for the client-side bindings.

Quote:

Originally Posted by No!No!No!Yes! (Post 657532)

Could you suggest any other "safe" "not-well-known" name to use here?

Well, anything within reason I guess :)

"it.nononoyes.qbw"? :P

Best regards.

Re: Help needed: DBUS signals not received by hildon-desktop widget (I need widget2widget & system2widget IPC)

Quote:

Originally Posted by No!No!No!Yes! (Post 657509)

Yes, you are right ... I was aware of those special functions/stubs for

but first time i tried I got and "assertion failed" notification stating that caller was not a hd_home_plugin_item.
However that could have been my mistake in calling the function back in my "try-this-and-see-what-happens" hours!!!

You could take a look at the code in gpesummary. Look at gpe_summary_plugin_init for the way I use hd_home_plugin_item_get_dbus_connection.

As for debugging these sorts of issues, it can be pretty horrible. I recommend using scratchbox, in an X86 session. Start up the hildon environment, then kill hildon-desktop and re-run it under gdb (see http://wiki.maemo.org/Using_Valgrind..._in_Scratchbox,
particularly the section on "Starting Maemo-Launched Application with Maemo-Summoner ").