 which the thread pool
object is at present either running in the pool or has queued for
execution.  This procedure will not throw.  It is also thread safe,
although it accesses the task number field outside the pool mutex and
therefore with relaxed memory ordering.  That enables this procedure
to be applied more efficiently for rate limiting purposes but the
result might at any one time be marginally out of date.
</p>
<p>This procedure is first available in version 0.12 of this library.
</p></dd></dl>

<dl