ActiveSupport::Subscriber
is an object set to consume ActiveSupport::Notifications
. The subscriber dispatches notifications to a registered object based on its given namespace.
An example would be an Active Record subscriber responsible for collecting statistics about queries:
module ActiveRecord
class StatsSubscriber < ActiveSupport::Subscriber
attach_to :active_record
def sql(event)
Statsd.timing("sql.#{event.payload[:name]}", event.duration)
end
end
end
After configured, whenever a “sql.active_record” notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event
) to the sql
method.
We can detach a subscriber as well:
ActiveRecord::StatsSubscriber.detach_from(:active_record)
Methods
- A
- D
- F
- M
- N
- R
- S
Class Public methods
attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false) Link
Attach the subscriber to a namespace.
# File activesupport/lib/active_support/subscriber.rb, line 34 def attach_to(namespace, subscriber = new, notifier = ActiveSupport::Notifications, inherit_all: false) @namespace = namespace @subscriber = subscriber @notifier = notifier @inherit_all = inherit_all subscribers << subscriber # Add event subscribers for all existing methods on the class. fetch_public_methods(subscriber, inherit_all).each do |event| add_event_subscriber(event) end end
detach_from(namespace, notifier = ActiveSupport::Notifications) Link
Detach the subscriber from a namespace.
# File activesupport/lib/active_support/subscriber.rb, line 49 def detach_from(namespace, notifier = ActiveSupport::Notifications) @namespace = namespace @subscriber = find_attached_subscriber @notifier = notifier return unless subscriber subscribers.delete(subscriber) # Remove event subscribers of all existing methods on the class. fetch_public_methods(subscriber, true).each do |event| remove_event_subscriber(event) end # Reset notifier so that event subscribers will not add for new methods added to the class. @notifier = nil end
method_added(event) Link
Adds event subscribers for all new methods added to the class.
# File activesupport/lib/active_support/subscriber.rb, line 68 def method_added(event) # Only public methods are added as subscribers, and only if a notifier # has been set up. This means that subscribers will only be set up for # classes that call #attach_to. if public_method_defined?(event) && notifier add_event_subscriber(event) end end
new() Link
subscribers() Link
Class Private methods
add_event_subscriber(event) Link
# File activesupport/lib/active_support/subscriber.rb, line 84 def add_event_subscriber(event) # :doc: return if invalid_event?(event) pattern = prepare_pattern(event) # Don't add multiple subscribers (e.g. if methods are redefined). return if pattern_subscribed?(pattern) subscriber.patterns[pattern] = notifier.subscribe(pattern, subscriber) end
remove_event_subscriber(event) Link
# File activesupport/lib/active_support/subscriber.rb, line 95 def remove_event_subscriber(event) # :doc: return if invalid_event?(event) pattern = prepare_pattern(event) return unless pattern_subscribed?(pattern) notifier.unsubscribe(subscriber.patterns[pattern]) subscriber.patterns.delete(pattern) end