An active actor manager iterates an active actor until its postfire()
returns false, or the director is requested to stop. If the active
actor has pull input and its prefire() returns false, the actor manager
will notify the CI director to process the pull request by the actor.
When the actor has a period parameter, the actor manager will
sleep between successive iterations of the actor for the duration
given by the parameter, in milliseconds. This is used to control the
execution rate of active actors that are always ready to produce the
next output or request the next input.