Dbus multiple threading problem

[Simon McVittie]

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On 22/05/12 11:38, Vinoth V wrote:
> but  I have requirement like message need to pass from server to client
> also.

That's possible.

> for every 2 mins server will send a specific details to its client, this
> msg should be initiated by the server and client should respond back...

That's possible. I'd do this as an asynchronous method call sent by the
"server" to the "client". This reverses their usual roles, but that's OK
- all processes on D-Bus are treated the same. Telepathy and BlueZ both
have situations where the process you'd normally think of as the
"server" calls methods on the process you'd normally think of as the
"client".

It has to be an asynchronous method call (send request, go back to your
main loop, get a callback called from your main loop later) because if
two processes try to make synchronous method calls to each other,
they'll typically deadlock while each waits for the other to reply.

You should make asynchronous method calls anyway, though; see
<http://smcv.pseudorandom.co.uk/2008/11/nonblocking/>.

> Is there any API avaliable in glib to do this or we need to create a
> another message bus for the client side to meet my requirement.

Export an object with a method from the "client" (e.g. with
g_dbus_connection_register_object()); make the "client" tell the
"server" its unique name somehow (e.g. call
g_dbus_connection_get_unique_name() and send that to the "server"); make
the "server" call the client's method by using that unique name.

> whether my requirement can be  achieved using signals ..?

You could do this with signals too, although method calls would probably
be easier to understand:

* emit signal with your "specific details" every 2 minutes
* your client responds to that signal by calling a method on the server

> but i need to
> send data structures as arguments ..
> maximum  three arugments i need to send from the server to client.

You can send nearly any data structure that you can encode into a
GVariant (exceptions: you can't send any type involving "maybe", you can
only send a dict-entry if it's in an array of dict-entry, and you can't
send empty tuples).

If you have a complex data structure you will need to work out how to
encode it as a D-Bus message (or, equivalently, as a GVariant without
using the features I mentioned).

    S