def kill_zombie_users(users)
      @mutex.synchronize do
        (@users - users - Set.new([@thaum_user])).each do |user|
          @users.delete(user)
        end
      end
    end
def kill_zombie_users(users)
      @mutex.synchronize do
        (@users - users - Set.new([@thaum_user])).each do |user|
          @users.delete(user)
        end
      end
    end
Removes all users from the UserList that don't share channels with the
 Thaum.