Multi{pointer,touch} & Userspace

[Florian Echtler]

Hello Jim,

> I worry about the use of UDP, at least for networked input devices.
> Losing some of the event stream (e.g. up events) can be very confusing
> to applications (not to mention device drivers). Wireless is unreliable;
> UDP does not guarantee reliability.  Latency with TCP is just as low
> (and bandwidth comparable) in the face of no packet loss (if TCP_NODELAY
> is set on the socket).
You are quite correct there. I simply chose UDP at first because in the
testing environment, everything runs on a single machine and UDP is the
fastest and easiest-to-implement cross-language message passing system.
In fact, all four daemons just expect classes derived from C++ iostream,
so in the single-machine scenario, you could just put all of them into
one multithreaded application and have them communicate internally.

> I've also been wondering about the relative merit its of an ad-hoc wire
> format (such as you've defined) for events versus something like XML,
> where parsers and extensibility is known.  But it's time for me to
> perform some experiments to understand the performance trade-offs,
> rather than hand-waving; your existing code trumps my unproven
> hypothesis, so I better write some code.
I tried to keep the library core as simple and portable as possible,
which is why I decided against XML.. not for performance reasons in the
first place, but rather to keep the dependencies down.

Yours, Florian


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