Pthreads in 6.0-CURRENT

I recently had to stress test a program that uses several thousands of
threads, and one of the machines I ran it was a uniprocessor Celeron
running at 1800 MHz with 512 MB of physical memory; the system I use as
a workstation at home.

During one of the tests, that used more than 12000 threads filling up
queues that were consumed by 4-10 queue runner threads, the following
appeared in top's output:

  PID USERNAME PRI NICE   SIZE    RES STATE    TIME   WCPU    CPU COMMAND
10244 giorgos  129    0   348M 43500K RUN      0:51 10.84% 10.79% many

At the same time, a buildworld was running in the background, I was
chatting on IRC with some friends, and in general continued to work on my
workstation as usual -- without any noticeable decrease in the perceived
performance of the system, despite the fact that a program suddenly fired
up so many threads and did its work.

Pretty impressive :-)

Many thanks to all the people who have been working so far to make thread
support so cool in FreeBSD 6.0-CURRENT!

- Giorgos