 thread may call it.
</p>
<p>If &rsquo;delta&rsquo; is positive and tasks are currently queued for execution, a
new thread or threads will be started for the queued tasks.  This
procedure may therefore throw an exception if the system is unable to
start the required new thread(s).  Because starting new threads can be
time consuming, to minimize contention new threads are started outside
the pool&rsquo;s mutex, although internal book-keeping is done within the
mutex.  One consequence is that if such an excep