Why does Akka leave all these threads parked?
<p>I'm using Akka to perform a bunch of very short tasks in parallel.  I create a parent Actor using <code>system.actorOf</code> that creates 25 other Actors using <code>context().actorOf</code>.  Then I call <code>context().stop(getSelf())</code> in the parent Actor, which should stop all the children.</p>

<p>I'm watching the thread states in VisualVM to learn a bit about how Akka works in the background, and I noticed that when I call <code>stop()</code> on the parent Actor, the threads spawned by Akka start slowly being killed one by one at different times, and the rest remain parked.  It was 10 minutes before all of the threads were killed, but here's a snapshot soon after I called <code>stop()</code>, where you can see a few threads in the default dispatcher being killed but the majority remaining parked:</p>

<p><a href="https://i.stack.imgur.com/Il1Oz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Il1Oz.png" alt="enter image description here"></a></p>

<p><strong>Why would these threads not all be killed at the same time?</strong> Why would they be killed one at a time seemingly arbitrarily? Why leave them any of them parked?  It doesn't seem that other actors I create reuse these threads.</p>