class ActiveSupport::Notifications::Fanout

def initialize
  @string_subscribers = Concurrent::Map.new { |h, k| h.compute_if_absent(k) { [] } }
  @other_subscribers = []
  @all_listeners_for = Concurrent::Map.new
  @groups_for = Concurrent::Map.new
  @silenceable_groups_for = Concurrent::Map.new
  super
end