[Interest] Q_PROPERTY notification across processes?

Mandeep Sandhu mandeepsandhu.chd at gmail.com
Mon May 20 07:46:38 CEST 2013

Suggestions in this thread (I'm researching further now):

>  - MPI (Arne suggested)
>  - QtDBus (Tony suggested)
>  - zeromp (Yves suggested)
>  - QxtRpc (Alex suggested)
> Interesting!! I was unaware of "zeromp", hadn't looked into MPI, and
> didn't think about QxtRpcService.  (I have lots of reading to do!)
> Mandeep (using Qxt's IPC/RPC) -- how many notifications-per-second does
> your system have, and do you have a feel for how it will scale (especially
> for the use model described above)?

Our usage was not heavy, as most of the communication happens on user
action and when it happens its probably just 2 or 3 invocations per second.

QxtRPC is not suitable for high volume traffic as the signals are
serialized into 'text' streams and sent over the comm channel.

For you use-case (and since you want to make it a generic solution), I
think DBus is the best bet as it uses a binary format for data transmission
which is much more efficient than what QxtRPC uses. DBus offers a lot more
functionality like object intorspection which can be used by others to see
what properties are exposed by such QObjects. Also hooking up signals using
proxy objects provided by QtDbus is very easy (you can simply chain out
your property change signals as Dbus signals).

What you have to see is whether such notifications happen over a bus or in
a peer-to-peer fashion. If there are a lot signals being generated then
it's best to avoid the bus (you'll probably use session bus as system bus
should be used only for system events) to avoid affecting other

Just my 2 cents.

Good luck,

> As an aside, it seems like this kind of interface would be useful in a
> number of settings.  It seems like the Q_PROPERTY/QML
> "notification-plumbing" allows "FOR-FREE" this type of cross-process
> synchronization.  If I get it working (seems do-able), I might be able to
> contribute the code to the Qt community (in the event the Community thinks
> it to be non-stupid as an approach).  -- I was just curious if anybody had
> this idea already, or (better-yet) had coded it already.  ;-))
> Thank you all for your input!  Looks like I have lots of reading to do...
> ;-)
> --charley
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