class ActiveSupport::Notifications::Fanout

def subscribe(pattern = nil, callable = nil, monotonic: false, &block)
  subscriber = Subscribers.new(pattern, callable || block, monotonic)
  synchronize do
    case pattern
    when String
      @string_subscribers[pattern] << subscriber
      @listeners_for.delete(pattern)
    when NilClass, Regexp
      @other_subscribers << subscriber
      @listeners_for.clear
    else
      raise ArgumentError,  "pattern must be specified as a String, Regexp or empty"
    end
  end
  subscriber
end