aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/lib/active_support/notifications.rb
blob: c45358bba9d739da197082715b7b49b4dde5a2e1 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
require 'active_support/notifications/instrumenter'
require 'active_support/notifications/fanout'
require 'active_support/per_thread_registry'

module ActiveSupport
  # = Notifications
  #
  # <tt>ActiveSupport::Notifications</tt> provides an instrumentation API for
  # Ruby.
  #
  # == Instrumenters
  #
  # To instrument an event you just need to do:
  #
  #   ActiveSupport::Notifications.instrument('render', extra: :information) do
  #     render text: 'Foo'
  #   end
  #
  # That executes the block first and notifies all subscribers once done.
  #
  # In the example above +render+ is the name of the event, and the rest is called
  # the _payload_. The payload is a mechanism that allows instrumenters to pass
  # extra information to subscribers. Payloads consist of a hash whose contents
  # are arbitrary and generally depend on the event.
  #
  # == Subscribers
  #
  # You can consume those events and the information they provide by registering
  # a subscriber.
  #
  #   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 this notification
  #     payload # => Hash, the payload
  #   end
  #
  # For instance, let's store all "render" events in an array:
  #
  #   events = []
  #
  #   ActiveSupport::Notifications.subscribe('render') do |*args|
  #     events << ActiveSupport::Notifications::Event.new(*args)
  #   end
  #
  # That code returns right away, you are just subscribing to "render" events.
  # The block is saved and will be called whenever someone instruments "render":
  #
  #   ActiveSupport::Notifications.instrument('render', extra: :information) do
  #     render text: 'Foo'
  #   end
  #
  #   event = events.first
  #   event.name      # => "render"
  #   event.duration  # => 10 (in milliseconds)
  #   event.payload   # => { extra: :information }
  #
  # The block in the <tt>subscribe</tt> call gets the name of the event, start
  # timestamp, end timestamp, a string with a unique identifier for that event
  # (something like "535801666f04d0298cd6"), and a hash with the payload, in
  # that order.
  #
  # If an exception happens during that particular instrumentation the payload will
  # have a key <tt>:exception</tt> with an array of two elements as value: a string with
  # the name of the exception class, and the exception message.
  #
  # As the previous example depicts, the class <tt>ActiveSupport::Notifications::Event</tt>
  # is able to take the arguments as they come and provide an object-oriented
  # interface to that data.
  #
  # It is also possible to pass an object as the second parameter passed to the
  # <tt>subscribe</tt> method instead of a block:
  #
  #   module ActionController
  #     class PageRequest
  #       def call(name, started, finished, unique_id, payload)
  #         Rails.logger.debug ['notification:', name, started, finished, unique_id, payload].join(' ')
  #       end
  #     end
  #   end
  #
  #   ActiveSupport::Notifications.subscribe('process_action.action_controller', ActionController::PageRequest.new)
  #
  # resulting in the following output within the logs including a hash with the payload:
  #
  #   notification: process_action.action_controller 2012-04-13 01:08:35 +0300 2012-04-13 01:08:35 +0300 af358ed7fab884532ec7 {
  #      controller: "Devise::SessionsController",
  #      action: "new",
  #      params: {"action"=>"new", "controller"=>"devise/sessions"},
  #      format: :html,
  #      method: "GET",
  #      path: "/login/sign_in",
  #      status: 200,
  #      view_runtime: 279.3080806732178,
  #      db_runtime: 40.053
  #    }
  #
  # You can also subscribe to all events whose name matches a certain regexp:
  #
  #   ActiveSupport::Notifications.subscribe(/render/) do |*args|
  #     ...
  #   end
  #
  # and even pass no argument to <tt>subscribe</tt>, in which case you are subscribing
  # to all events.
  #
  # == Temporary Subscriptions
  #
  # Sometimes you do not want to subscribe to an event for the entire life of
  # the application. There are two ways to unsubscribe.
  #
  # WARNING: The instrumentation framework is designed for long-running subscribers,
  # use this feature sparingly because it wipes some internal caches and that has
  # a negative impact on performance.
  #
  # === Subscribe While a Block Runs
  #
  # You can subscribe to some event temporarily while some block runs. For
  # example, in
  #
  #   callback = lambda {|*args| ... }
  #   ActiveSupport::Notifications.subscribed(callback, "sql.active_record") do
  #     ...
  #   end
  #
  # the callback will be called for all "sql.active_record" events instrumented
  # during the execution of the block. The callback is unsubscribed automatically
  # after that.
  #
  # === Manual Unsubscription
  #
  # The +subscribe+ method returns a subscriber object:
  #
  #   subscriber = ActiveSupport::Notifications.subscribe("render") do |*args|
  #     ...
  #   end
  #
  # To prevent that block from being called anymore, just unsubscribe passing
  # that reference:
  #
  #   ActiveSupport::Notifications.unsubscribe(subscriber)
  #
  # == Default Queue
  #
  # Notifications ships with a queue implementation that consumes and publish events
  # to log subscribers in a thread. You can use any queue implementation you want.
  #
  module Notifications
    class << self
      attr_accessor :notifier

      def publish(name, *args)
        notifier.publish(name, *args)
      end

      def instrument(name, payload = {})
        if notifier.listening?(name)
          instrumenter.instrument(name, payload) { yield payload if block_given? }
        else
          yield payload if block_given?
        end
      end

      def subscribe(*args, &block)
        notifier.subscribe(*args, &block)
      end

      def subscribed(callback, *args, &block)
        subscriber = subscribe(*args, &callback)
        yield
      ensure
        unsubscribe(subscriber)
      end

      def unsubscribe(args)
        notifier.unsubscribe(args)
      end

      def instrumenter
        InstrumentationRegistry.instrumenter_for(notifier)
      end
    end

    # This class is a registry which holds all of the +Instrumenter+ objects
    # in a particular thread local. To access the +Instrumenter+ object for a
    # particular +notifier+, you can call the following method:
    #
    #   InstrumentationRegistry.instrumenter_for(notifier)
    #
    # The instrumenters for multiple notifiers are held in a single instance of
    # this class.
    class InstrumentationRegistry # :nodoc:
      extend ActiveSupport::PerThreadRegistry

      def initialize
        @registry = {}
      end

      def instrumenter_for(notifier)
        @registry[notifier] ||= Instrumenter.new(notifier)
      end
    end

    self.notifier = Fanout.new
  end
end