Sending a
PoisonPill to an will stop the actor when the message is processed.
PoisonPill is enqueued as ordinary messages and will be handled after messages that were already queued in the mailbox.
See also Kill which causes the actor to throw an ActorKilledException when it processes the message, which gets handled using the normal supervisor mechanism, and IActorContext.Stop which causes the actor to stop without processing any more messages.
