Unix FD Passing

[Lennart Poettering]

On Mon, 04.05.09 19:38, Simon McVittie (simon.mcvittie at collabora.co.uk) wrote:

> 
> On Mon, 04 May 2009 at 19:44:41 +0200, Lennart Poettering wrote:
> > On Mon, 04.05.09 16:53, Alp Toker (alp at atoker.com) wrote:
> > > Thanks for paying attention to this. ndesk-dbus is actively using 'f'
> > > for 32 bit single precision floating point values and dbus-java and
> > > dbus-python support it as well now to some extent too I believe.
> > 
> > Uh. Could you please post this upstream to the spec, then? If it's
> > that well accepted then this should really be added to the spec!
> 
> FYI, the extent of float32 support in dbus-python is that the C part contains
> #ifdef'd code for it at Alp's urging; it should work, but has never been
> compiled, let alone tested. So, don't consider me to be part of the float32
> implementor cabal :-)
> 
> I seem to remember someone benchmarked sending messages with arrays of 32- and
> 64-bit floats and was unable to find a performance difference, but I can't
> find a URL.

Oh, I absolutely believe in the validity of having float32 in the
spec. In fact coming from an audio background I can say that float32
is one of the most often used types for audio samples and for good
reasons. 32bit floats already give about 10bit of headroom beyond the
theoretic limits of DACs (in the real world even more) Using 64bit fp
samples hence has only minimal (if not none) benefits at the price of
doubling the memory usage/bandwith requirements. Now D-Bus isn't a
particularly good choice for exchanging larger amounts of sample data
right now, but that doesn't change the fact that float32 is very
useful to have and very natural for all things audio.

It's not that I picked 'f' for the unix fd type because I thought
having float32 in D-Bus was a bad idea. I did it because I wasn't aware
that there was actual code using that type right now and because all
other letters that came to my mind were already taken (u, d, ...).

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/           GnuPG 0x1A015CC4