Question on service activation

[Kevin Krammer]

Hi Havoc,

thanks for responding.

On Thursday 22 February 2007 14:46, Havoc Pennington wrote:
> Kevin Krammer wrote:
> > Examples from the Maemo documentation and an activation tutorial linked
> > from the D-Bus tutorial suggest that interface name == D-Bus name ==
> > object path (with slash as separator), e.g. a .service file specifying a
> > service "org.example.Foo" will result in a process available at D-Bus
> > name "org.example.Foo", with an object at "/org/example/Foo" having the
> > interface "org.example.Foo"
>
> When the three line up, it is just a coincidence - for example I
> recently defined a "Prefs" interface which was implemented by a couple
> different object paths under a couple different bus names.

I see, we were already quite sure about this but there were too many such 
examples to not take it into consideration.

> > However, we weren't sure how service providers (i.e. processes with a
> > D-Bus connection providing interface implementations) would specify
> > multiple interfaces.
>
> Interfaces are implemented by objects within a process, while bus names
> are owned on the bus (by a process's connection).

Yes, that's what I tried to convey :)

> > For example consider PIM interfaces (kept short to ease typing):
> > pim.EMail, pim.Contacts, pim.Calendar.
>
> Do you mean interface or bus name here? (just to be sure)

interfaces

> > A "just email" application like Thunderbird would probably just implement
> > pim.EMail and pim.Contacts, a full PIM suite like Evolution would
> > implement all.
> >
> > (1) If none if the is running yet and an application would make a call to
> > pim.Contacts, will the bus wait until it has registered all its names?
>
> If you have multiple bus names then for a given activation, the bus will
> only care about one of them. i.e. it will only block the pim.Contacts
> call until pim.Contacts has an owner.

Yeah, thought so, but we had to make sure.

> > (2) Is there a race condition if two applications activate two different
> > services?
>
> Bus name ownership is only atomic for a single bus name. So yes you
> could get different apps owning the different names.
>
> > (3) If Evolution is the default handler as configured by the desktop, can
> > Thunderbird be prevented from claiming the default names if started
> > manually?
>
> Not right now. It's not clear this is right anyway (if someone has
> thunderbird open, maybe it should be used for mail - at least, it seems
> as good a guess as any)

Well, from my point of view I want to have my preferred mail application to 
handle mails, which is the one I have told by desktop to consider the 
default.

> You can imagine various solutions, obviously, but in general nobody has
> yet defined the connection between the default handler choices and dbus
> activation.

I see. We were basically discussion the design and even the need for a broker 
to map from a service (interface) to a service provider (D-Bus name)

Since a couple of examples suggested that people are using the interface name 
and D-Bus name interchangably, we'd rather ask if this was just concidentally 
or meant to work this way.

It wouldn't have made sense to continue designing a service broker if that's 
already handled by the existing infrastructure.

Cheers,
Kevin

-- 
Kevin Krammer, KDE developer, xdg-utils developer
KDE user support, developer mentoring
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