PropertiesChanged signal

Thiago Macieira thiago at
Sat May 8 01:37:44 PDT 2010

Em Sábado 8. Maio 2010, às 10.29.06, Michael 'Mickey' Lauer escreveu:
> Am Samstag, den 08.05.2010, 09:24 +0200 schrieb Thiago Macieira:
> > Em Sexta-feira 7. Maio 2010, às 23.10.00, Michael 'Mickey' Lauer escreveu:
> > > And while we're there we could/should also fix the client-based signal
> > > matching, which is IMO one of the major design flaws in DBus.
> > > I know that the desktop people don't care, but still...
> > 
> > What is the issue?
> Two issues:
> 1.) Listeners are always woken up on any kind of signals (to run the
> match function), no matter whether they are listening to a certain
> signal or not. That's a waste of CPU hence battery.

Wrong. Listeners are woken up if there's a message (a signal) that matches 
their listening rules. If they are woken up by a message that they weren't 
interested in, it's because the listener added a rule that was too broad.

The listener must be fixed to listen to the specific signals it's interested in.

> 2.) Signals are being computed and sent no matter whether anyone is
> listening or not. Again a terrible waste of CPU.

That is true and is the one I'm trying to avoid wasting more on. I like 
David's idea of making all senders be notified of signal connection, but it's 
going to take some more discussion to hash out a full proposal that works.

> Both issues are commonly worked around by introducing additional
> application-specific protocols, such as the 'agent-based' approach we
> see in bluez, connman, etc.; still it's merely done due to the lack of
> server-side signal handling.

Thiago Macieira - thiago (AT) - thiago (AT)
  Senior Product Manager - Nokia, Qt Development Frameworks
      PGP/GPG: 0x6EF45358; fingerprint:
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