 which is the default,
that procedure will not return until all tasks previously added to the
pool have completed.  If set to #t, the thread-pool-stop! procedure
will return immediately, before all tasks have finished.
</p>
<p>The #:max-threads, #:non-blocking and #:idle settings may subsequently
be altered by applying the thread-pool-change-max-threads!,
thread-pool-set-non-blocking! or thread-pool-set-idle-time! procedure
to the pool.
</p>
<p>This procedure will throw an exception if the system is unable 