(Round 3) Proposed patch to support: draft-zeilenga-ldap-c-api-concurrency

[Doug Leavitt <doug.leavitt@oracle.com>]

 Since my last patch submission (Round2) I spent a considerable
amount of time performing performance analysis of my proposed
both client side and server side.

The client side testing primarily consisted of running parallel
copies of slapd-mtread and monitoring in real time with dtrace
to monitor the behavior of all the concurrent threads in clients
looking for signs of thread starvation.  I was not able to find any.

On the server side I performed similar testing while using modified
versions of the test036-meta-concurrency and test020-proxycache
test cases.  Again looking for thread starvation.

Additionally, on the server side I setup single server and proxy cache
server environments, in combination with slamd to perform head to
head comparisons of
    HEAD (most recently as of 10/7/10)
vs.
    HEAD (most recently as of 10/7/10) and the round 3 MT patches

to see if there was any performance degradations or other
performance issues, especially related to situations where slapd
was using libldap_r as part of various backends.

The results of the head to head comparisons, especially in the
proxycache situation, show a 3% performance improvement with
the MT patches over the HEAD without the patches.

The reason according to dtrace outputs is that there are now cases,
especially in ldap_result where my proposed patch has up to 50% less calls
to thread_lock/unlock than are performed in the current HEAD.

All of the head to head dslam/dtrace results are included along with
the other patch materials.

The proposed patch details are located here:

http://cr.opensolaris.org/~djl/openldap-codereview-r3/

Details about the contents of
http://cr.opensolaris.org/~djl/openldap-codereview-r3/dtrace
is located here:
http://cr.opensolaris.org/~djl/openldap-codereview-r3/README.txt

Doug.