protected TopicLike(TimeSpan emptyTimeToLive)
{
Subscribers = new HashSet<IActorRef>();
EmptyTimeToLive = emptyTimeToLive;
PruneInterval = new TimeSpan(emptyTimeToLive.Ticks / 2);
PruneCancelable = Context.System.Scheduler.ScheduleTellRepeatedlyCancelable(PruneInterval, PruneInterval, Self, Prune.Instance, Self);
}