subscribe

Subscribe to a given event name with the passed block.

You can subscribe to events by passing a String to match exact event names, or by passing a Regexp to match all events that match a pattern.

ActiveSupport::Notifications.subscribe(/render/) do |*args|
  @event = ActiveSupport::Notifications::Event.new(*args)
end

The block will receive five parameters with information about the event:

ActiveSupport::Notifications.subscribe('render') do |name, start, finish, id, payload|
  name    # => String, name of the event (such as 'render' from above)
  start   # => Time, when the instrumented block started execution
  finish  # => Time, when the instrumented block ended execution
  id      # => String, unique ID for the instrumenter that fired the event
  payload # => Hash, the payload
end

If the block passed to the method only takes one parameter, it will yield an event object to the block:

ActiveSupport::Notifications.subscribe(/render/) do |event|
  @event = event
end

Raises an error if invalid event name type is passed:

ActiveSupport::Notifications.subscribe(:render) {|*args| ...}
#=> ArgumentError (pattern must be specified as a String, Regexp or empty)