Programming technique for non-forking servers?

Hello people,

can anyone point me to some book, or URL(s), where the
programming technique for writing non-forking network server
daemons is described in details? with caveats, non-obvious
places...

I mean those like Squid, Harvest cached, probably Gated
(there is also a non-forking WWW server somewhere, but
I forgot it's name, for a pity). AFAIK they are written
around a huge select(), and are using asynchronous I/O.
Yes, there are sources, but I'd really like to read
some general theory on the subject.

Thanks in advanse!

--
		Best,
			Andrew Stesin
		nic-hdl: ST73-RIPE