Sander van Grieken
sander at 3v8.net
Thu Feb 28 20:06:06 CET 2008
On Thursday 28 February 2008 19:06:44 Shawn Rutledge wrote:
> On Thu, Feb 28, 2008 at 5:38 AM, Tilman Baumann <tilman at baumann.name> wrote:
> > Shawn Rutledge wrote:
> > > On Wed, Feb 27, 2008 at 10:46 AM, Tilman Baumann <tilman at baumann.name>
> > >> First, im not in any way a authority on this.
> > >> But i would say classic IPC is everything but d-bus.
> > >
> > > Well it's not old enough to be classic yet. :-)
> > >
> > > But I'm curious, what do you dislike about using it for IPC? (I'm
> > > just learning how to use it.)
> > Foremost Performance.
> > D-Bus is a abused unix domain socket interface for broadcasts and
> > multicast.
> Once I was messing with broadcast IP packets (I wrote a network
> caller-ID notifier and client program) and the trouble was that only
> one listener could be registered on a machine's broadcast address, so
> it can really be used only from one process on one machine to one
> process on another. But for multicast, multiple processes can listen
> on the same IP address and port, right?
No. multicast can only deliver the same packet to different IP addresses.
> So isn't it true that
> multicast UDP packets could be used both for between-process
> notifications on the same machine, and also across a network? Why
> wouldn't DBus have been based on that, rather than each process
> needing to keep a connection open to the bus daemon?
Maybe I don't know dbus well enough, but it seems to me that a process merely
registers a session with dbus, not keeping a connection open. Going through
the network stack is much slower than using assisted IPC (that's what d-bus
> DBus is not usually used for between-machine communication, right? So
> I figured the conclusion is that it doesn't scale well.
You could always use corba for that. It would be just a matter of writing an
IDL for the particular object you want to expose.
> It also seems to me that DBus has more namespace qualifiers than you
> need: service, interface, path, and method-name. I think I understand
> the inspiration behind all of those, but I believe path and
> method-name would have been enough. It's more string
> parsing/comparing work for the daemon to qualify incoming packets on
> the basis of 4 things rather than just 2. It would be a nice clean
> conceptual model to say that there is simply a tree of callbacks, and
> you need to provide the path to the node of the tree that you want.
> But "interface" seems thrown in as an afterthought, inspired by Java;
> and both interface and service resemble reverse-domain-names. But a
> domain name addresses a specific machine; an interface or a service is
> just an arbitrary namespace division.
Well not really, since a service could conform to multiple interfaces. It
enables applications to call a service, even if it doesn't know the actual
service, but only one of its interfaces.
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