diff --git a/guides/source/active_support_instrumentation.md b/guides/source/active_support_instrumentation.md index fba7a633c65..5612de7f202 100644 --- a/guides/source/active_support_instrumentation.md +++ b/guides/source/active_support_instrumentation.md @@ -10,9 +10,9 @@ In this guide, you will learn how to use the instrumentation API inside of Activ After reading this guide, you will know: * What instrumentation can provide. +* How to add a subscriber to a hook. * The hooks inside the Rails framework for instrumentation. -* Adding a subscriber to a hook. -* Building a custom instrumentation implementation. +* How to build a custom instrumentation implementation. -------------------------------------------------------------------------------- @@ -23,7 +23,83 @@ The instrumentation API provided by Active Support allows developers to provide For example, there is a hook provided within Active Record that is called every time Active Record uses an SQL query on a database. This hook could be **subscribed** to, and used to track the number of queries during a certain action. There's another hook around the processing of an action of a controller. This could be used, for instance, to track how long a specific action has taken. -You are even able to create your own events inside your application which you can later subscribe to. +You are even able to [create your own events](#creating-custom-events) inside your application which you can later subscribe to. + +Subscribing to an event +----------------------- + +Subscribing to an event is easy. Use `ActiveSupport::Notifications.subscribe` with a block to +listen to any notification. + +The block receives the following arguments: + +* The name of the event +* Time when it started +* Time when it finished +* A unique ID for the instrumenter that fired the event +* The payload (described in future sections) + +```ruby +ActiveSupport::Notifications.subscribe "process_action.action_controller" do |name, started, finished, unique_id, data| + # your own custom stuff + Rails.logger.info "#{name} Received! (started: #{started}, finished: #{finished})" # process_action.action_controller Received (started: 2019-05-05 13:43:57 -0800, finished: 2019-05-05 13:43:58 -0800) +end +``` + +If you are concerned about the accuracy of `started` and `finished` to compute a precise elapsed time then use `ActiveSupport::Notifications.monotonic_subscribe`. The given block would receive the same arguments as above but the `started` and `finished` will have values with an accurate monotonic time instead of wall-clock time. + +```ruby +ActiveSupport::Notifications.monotonic_subscribe "process_action.action_controller" do |name, started, finished, unique_id, data| + # your own custom stuff + Rails.logger.info "#{name} Received! (started: #{started}, finished: #{finished})" # process_action.action_controller Received (started: 1560978.425334, finished: 1560979.429234) +end +``` + +Defining all those block arguments each time can be tedious. You can easily create an `ActiveSupport::Notifications::Event` +from block arguments like this: + +```ruby +ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args| + event = ActiveSupport::Notifications::Event.new *args + + event.name # => "process_action.action_controller" + event.duration # => 10 (in milliseconds) + event.payload # => {:extra=>information} + + Rails.logger.info "#{event} Received!" +end +``` + +You may also pass block with only one argument, it will yield an event object to the block: + +```ruby +ActiveSupport::Notifications.subscribe "process_action.action_controller" do |event| + event.name # => "process_action.action_controller" + event.duration # => 10 (in milliseconds) + event.payload # => {:extra=>information} + + Rails.logger.info "#{event} Received!" +end +``` + +Most times you only care about the data itself. Here is a shortcut to just get the data. + +```ruby +ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args| + data = args.extract_options! + data # { extra: :information } +end +``` + +You may also subscribe to events matching a regular expression. This enables you to subscribe to +multiple events at once. Here's how to subscribe to everything from `ActionController`. + +```ruby +ActiveSupport::Notifications.subscribe /action_controller/ do |*args| + # inspect all ActionController events +end +``` + Rails framework hooks --------------------- @@ -631,81 +707,6 @@ Rails | `:message` | The deprecation warning | | `:callstack` | Where the deprecation came from | -Subscribing to an event ------------------------ - -Subscribing to an event is easy. Use `ActiveSupport::Notifications.subscribe` with a block to -listen to any notification. - -The block receives the following arguments: - -* The name of the event -* Time when it started -* Time when it finished -* A unique ID for the instrumenter that fired the event -* The payload (described in previous sections) - -```ruby -ActiveSupport::Notifications.subscribe "process_action.action_controller" do |name, started, finished, unique_id, data| - # your own custom stuff - Rails.logger.info "#{name} Received! (started: #{started}, finished: #{finished})" # process_action.action_controller Received (started: 2019-05-05 13:43:57 -0800, finished: 2019-05-05 13:43:58 -0800) -end -``` - -If you are concerned about the accuracy of `started` and `finished` to compute a precise elapsed time then use `ActiveSupport::Notifications.monotonic_subscribe`. The given block would receive the same arguments as above but the `started` and `finished` will have values with an accurate monotonic time instead of wall-clock time. - -```ruby -ActiveSupport::Notifications.monotonic_subscribe "process_action.action_controller" do |name, started, finished, unique_id, data| - # your own custom stuff - Rails.logger.info "#{name} Received! (started: #{started}, finished: #{finished})" # process_action.action_controller Received (started: 1560978.425334, finished: 1560979.429234) -end -``` - -Defining all those block arguments each time can be tedious. You can easily create an `ActiveSupport::Notifications::Event` -from block arguments like this: - -```ruby -ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args| - event = ActiveSupport::Notifications::Event.new *args - - event.name # => "process_action.action_controller" - event.duration # => 10 (in milliseconds) - event.payload # => {:extra=>information} - - Rails.logger.info "#{event} Received!" -end -``` - -You may also pass block with only one argument, it will yield an event object to the block: - -```ruby -ActiveSupport::Notifications.subscribe "process_action.action_controller" do |event| - event.name # => "process_action.action_controller" - event.duration # => 10 (in milliseconds) - event.payload # => {:extra=>information} - - Rails.logger.info "#{event} Received!" -end -``` - -Most times you only care about the data itself. Here is a shortcut to just get the data. - -```ruby -ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args| - data = args.extract_options! - data # { extra: :information } -end -``` - -You may also subscribe to events matching a regular expression. This enables you to subscribe to -multiple events at once. Here's you could subscribe to everything from `ActionController`. - -```ruby -ActiveSupport::Notifications.subscribe /action_controller/ do |*args| - # inspect all ActionController events -end -``` - Creating custom events ----------------------