Fwd: Circular calls with DBUS

[Rob Taylor]

John (J5) Palmieri wrote:
> On Fri, 2007-03-23 at 15:30 +0000, Rob Taylor wrote:
>> Jacques Guillou wrote:
>>> Is there a way to configure the GLib binding in such a way that an incoming
>>> message can be preocessed even if the main loop execution is stopped into a
>>> synchronous call (waiting for its answer) ?
>>> Would that be safe ?
>>>
>>> I really think using asynchronous calls only would make a system much more
>>> complex than it would be if synchronous calls were allowed.
>>>
>> Async call handling is the only way to (possibly) totally avoid
>> deadlock, any other scheme leads to subtle deadlock cases (see mailing
>> list history for a discussion of this, in respect to DCOP deadlock
>> breaking).
>>
>> Note that only code providing objects on the bus needs to use async
>> calling, normal clients can still use synchronous calls.
> 
> I never like to say this because of the "programmers are lazy" syndrome.
> I think learning how to do async calls and using them everywhere will
> make them much easier to deal with in the long run (sure mainloop event
> programming was once hard to deal with but when is the last time you
> wrote something serious without a mainloop?).  


Yeah, I agree, it makes sense to encourage async usage everywhere for
glib based code, at least.

> That being said we should
> look at our bindings and figure out if there is a way to make chaining
> async calls easier.  In python we could do something similar to twisted
> deferred methods.

Hmm, it may be a lack of imagination on my part, but for c, I can't
think of anything easier than callbacks :/ We could possibly do some
crazy multiple-stack coroutine-type stuff, I guess, but that'd be a
portability nightmare. Of course, running the mainloop when making
synchronous calls gives a pretty similar effect, but as Simon said, it
violates the principle of least surprise and also could lead to
unpredictable stack growth and interesting side effects. I gather this
is what Qt4 currently does, so I'd be interested to hear what Thiago has
to say on it.

Thanks,
Rob Taylor

Thanks,
Rob Taylor