[distcc] load management

[Jake McGuire]

I am planning to start working on adding load management enhancements 
to distcc for use at our company, but wanted to make sure that no one 
was almost done fixing the problem and also make sure that I didn't 
spend a bunch of time making my changes and have them rejected.

A brief summary of my proposal:

1) have distccd listen on a UDP port for "status requests"
   a) when distccd gets a request on this port, send back status info to 
the requester
     1) number of active compilation requests
     2) "server weight"
     3) maximum connections
     4) other status information TBD
   b) forking client
     1) just look at dcc_nkids variable
   c) preforking client
     1) have each child lock/unlock a file when it starts/finishes 
compilation
     2) distccd tries to lock each file; number of locked files = number 
of active connections
3) on startup, distcc determines appropriate server to send request to
   a) poll all servers in host list - wait until all respond or 0.1 
seconds, whichever comes first
   b) multiply connection count by weight, take minimum result, send 
request to that server

"least connection" loadbalancing actually does a very good job of 
spreading the load around - faster machines process connections faster 
and so end up getting more of the work.  Weighting is more or less 
optional, but can be used if you want some machines in the cluster to 
be dedicated compilation boxes and others are also used for other 
things.

Thoughts?  I'll probably get to this next week or maybe later this week.

-jake