Re: [RFC 1/2] gdbus: Add g_dbus_flush_properties()

[Vinicius Costa Gomes <vinicius.gomes@openbossa.org>]

Hi Lucas,

On 14:33 Wed 24 Apr, Lucas De Marchi wrote:
> On Wed, Apr 24, 2013 at 10:58 AM, Johan Hedberg <johan.hedberg@gmail.com> wrote:
> > Hi,
> >
> > On Fri, Apr 19, 2013, Vinicius Costa Gomes wrote:
> >> On 09:30 Fri 19 Apr, Luiz Augusto von Dentz wrote:
> >> > What about creating a new flag for properties that need to emit a
> >> > signal immediately when they change?
> >>
> >> That would also solve the problem.
> >>
> >> The way I see it, we should still not make any guarantees about when
> >> a propery changed signal will be emitted, only when the API behaviour
> >> requires, we use some kind of barrier to keep the ordering in check.
> >>
> >> And having a function to call we make it easier to detect when this
> >> is abused, i.e. we know there's something very wrong if there's a flush
> >> after each emit.
> >
> > Is this where the discussion got stuck? Since this feature is really
> > only needed for quite exceptional situations if an API change needs to
> > be done I'd be in favor of a separate flush function.
> >
> > Another option is to make *all* D-Bus messages that gdbus sends to use
> > an idle callback, including method calls and returns. In the idle
> > callback the messages would be sent in the same order as they were added
> > to the send queue. This would not require any changes to the gdbus API.
> 
> 
> ugh.. no. This doesn't play well with sending the message directly
> through libdbus.
> 
> When we implemented the properties interface, the manner we talked
> about doing this (if it was indeed needed) was mostly what Luiz is
> saying now. I think I even sent a patch to this mailing list
> containing this flag. You would add something like:
> 
> G_DBUS_PROPERTY_FLAG_IMMEDIATE (or some better naming). Then
> g_dbus_emit_property_changed() would check this flag, in which case
> process_changes() would be called synchronously. I don't see why this
> wouldn't solve your problem and it doesn't require an API change. For
> the exceptional cases in which this is needed, we add such flag. And
> if a property needs to be sent immediately in one place I think it
> always will. Or am I missing something?

I understand the problem a little differently. To solve this problem in the
general sense, I want the remote application to have an updated view of the
device object before receiving the NewConnection() call.

Having some properties (Paired and UUIDs) marked as immediate would only solve
this particular problem.

But it could be that I am blowing this out of proportion.

> 
> I can send the patch again if you want.
> 
> Lucas De Marchi


Cheers,
-- 
Vinicius