ITS#4943 tpool.c, thread pools

[Howard Chu <hyc@symas.com>]

I presume we can close this ITS now.

I've been running some tests on a quad-processor AMD system, and seeing a lot 
of mutex contention in the frontend. It looks like the current threadpool and 
connection manager architecture are a bad fit for a NUMA system like this. I'm 
planning to add support for multiple thread pools (one per CPU would be the 
idea) and multiple listener threads to slapd.

As a first step, after 2.4.6 is released, I'm going to unifdef the 
SLAPD_LIGHTWEIGHT_DISPATCHER symbol and delete the old dispatcher code.

Based on some experimental changes I've already made, I see a difference 
between 25K auths/sec with the current code, vs 39K auths/sec using separate 
thread pools.
--
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP     http://www.openldap.org/project/