Re: DarkStarMy experience is that DarkStar never reached its potential, for a few reasons.
One was the "everything's a connected mesh of objects" problem, which means that locking turns out to be more global than you'd want.
The second is that it never scaled beyond a single node -- adding nodes made it *slower*.
The third is that the "potential" was always hyped in the marketing, and always years and years ahead of actual delivery (and still is).
Re: What language/framework to use
Which language you use doesn't matter much. How you use that language is much more important.
Re: Where you're at in designing your massive system
When you say "I want to access values of the other connections," it makes it sound as if you don't have your data architecture and consistency model down yet. You need to first decide what kinds of data is owned where, how out of data it is allowed to be at what point at any one time, what kind of connection quality you can require from your clients, how many consistency classes you'll need (with ranges from "always synchronously ACID backed into database" all the way to "ephemerally synthesized on the client")
Once you have all that, you can start figuring out how to partition the simulation and other operations that go server-side. For example, if locality of space is most important, then you'd probably partition all services for a certain geographic area into a single physical node. If locality of processing is more important, then perhaps you'll put all things about a certain subsystem on a specific node.
Re: What I/we ended up doing
I've spent the last year writing a massively scaled system in Erlang, and while it was alien as all get out to start out with, it's very clear that it's a system that has been used in production for large, distributed systems. It's not a toy, like many other pretenders, and it stands up to the pressure when you do real things with it. You might want to look at the following article for starting out:
If you use C++, then I suggest using boost::asio for the threading and async networking/IO bit.
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