Efficient ways to implement bi-directional comm programs?

[Roy Smith]

	Programs like rlogin, telnet, tip, kermit, etc. need to implement
bi-directional communication; whatever you type has to be forwarded to "the
other end" and whatever comes in from "the other end" has to be forwarded to
your screen.  The two ways I know to do this are to 1) use two processes, each
handling one side of the connection, or 2) use a single process to handle both
sides, select(2)ing on the 2 input file descriptors.

	Are the any generally-applicable rules as to which is more efficient
(you may define efficiency in any terms you like, but please show all work to
receive full credit).  My gut feeling is that a single process would be more
efficient in terms of memory, and probably in terms of CPU as well.  I suppose
a third alternative would be polling in a single process using non-blocking
reads on both file descriptors, but I can't imagine that would do anything
other than eat CPU time like crazy.
-- 
Roy Smith, System Administrator
Public Health Research Institute
455 First Avenue, New York, NY 10016
{allegra,philabs,cmcl2,rutgers}!phri!roy -or- phri!roy at uunet.uu.net