Make an Event of It!

Jason Clark
@jasonrclark
Ruby Agent Engineer
Make an Event of It!
Evented Patterns in Ruby
Tuesday, April 22, 14

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Storytime!

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class UsersController < ApplicationController
def create
@user = User.new(user_params)
if @user.save
redirect_to @user
else
render 'new'
end
end
end

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def create
if @user.save
UserMailer.welcome_email(@user).deliver
redirect_to @user
...
end
end
end

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def create
if @user.save
Analytics.notify_user_creation(@user)
redirect_to @user
...
end
end
end

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def create
if @user.save
Crm::Gateway.new(@user.id, @user.name, ...)
redirect_to @user
...
end
end
end

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def create
if @user.save
Crm::Gateway.new(@user.id, @user.name, ...)
Resque.enqueue(AlertTheSocials, @user.id)
redirect_to @user
...
end
end
end

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https://ﬂic.kr/p/6qdTC1

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Where Are We Going?
The Pattern
Coupling
Mechanics
Responsibilities
12

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The Pattern
http://ﬂic.kr/p/6K9jC4

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14

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15

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Events Aren't
(Necessarily)
16
Asynchronous
IO related
Distributed
Complicated

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17

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17
Notiﬁer

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17
Notiﬁer
Subscriber
Subscriber
Subscriber

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17
Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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18
Why Not Methods?

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19
Notiﬁer
Subscriber
Subscriber
Subscriber
Eventing
System

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Why Not Callbacks?
20

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21
class Subscription < ActiveRecord::Base
before_create :record_signup
private
def record_signup
self.signed_up_on = Date.today
end
end

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Where Are We Going?
The Pattern
Coupling
Mechanics
Responsibilities
22

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23
Internal Coupling
http://ﬂic.kr/p/KikA9

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newrelic_rpm
24

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newrelic_rpm
24
app start

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newrelic_rpm
24
app start connect()
New Relic
Server

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newrelic_rpm
{server conﬁg}
24
app start connect()
New Relic
Server

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newrelic_rpm
{server conﬁg}
24
app start connect()
New Relic
Server
?

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newrelic_rpm
25
def connect()
config = config_from_server()
finish_setup(config)
end

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newrelic_rpm
26
def finish_setup(config)
add_naming_rule(config['rules'])
@cross_app_tracing.set_key(config)
@js_instrumentor.log_config(config)
@beacon = Beacon.new
end

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newrelic_rpm
27
def test_finish_setup_naming_rules
config = { 'rules' => [...] }
@agent.finish_setup(config)
assert_equal 2, @agent.transaction_rules.size
end

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28
@agent.cross_app_tracing.stub(:set_key)
@agent.js_instrumentor.stub(:log_config)
config = { 'rules' => [...] }
end
newrelic_rpm

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29
end
newrelic_rpm

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30
end
newrelic_rpm

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31
class Beacon
def initialize
# Your code is bad and you should feel bad
Net::HTTP.get("http://somewhere.com")
end
end
newrelic_rpm

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32
@agent.cross_app_tracing.stub(:set_key)
@agent.js_instrumentor.stub(:log_config)
Beacon.stub(:new).return(stub("fake beacon"))
config = { 'rules' => [...] }
end
newrelic_rpm

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33
end
newrelic_rpm

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34
events.notify(:configured)
end
newrelic_rpm

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35
class Beacon
def initialize
events.subscribe(:configured) do
Net::HTTP.get("http://...")
end
end
end
newrelic_rpm

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36
def test_finish_setup_notifies
called = false
@events.subscribe(:configured) do
called = true
end
@agent.finish_setup({})
assert called
end
newrelic_rpm

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37
def test_add_naming_rules
config = { 'rules' => [...] }
@agent.add_naming_rules(config)
end
newrelic_rpm

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More Independent
Classes
39

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Domain Language
40

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Implicit Ordering
41

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Debugging
42

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Performance
43

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http://ﬂic.kr/p/euQpT
External Coupling

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45
newrelic_rpm

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45
Javascript insertion
newrelic_rpm

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45
Error collection
newrelic_rpm

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45
Cross application tracing
Error collection
newrelic_rpm

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46
No Setup Please!
newrelic_rpm

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47
module NewRelic::Rack
class AgentHooks
def call(env)
notify(:before_call, env)
result = @app.call(env)
notify(:after_call, env, result)
result
end
end
end
newrelic_rpm

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48
class CrossAppTracing
def initialize
events.subscribe(:before_call) do |e|
process_request(e)
end
...
end
end
newrelic_rpm

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Ever Heard of
Composition?
49

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Looser Coupling
50

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Compatibilty
Layer
51

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Where Are We Going?
The Pattern
Coupling
Mechanics
Responsibilities
52

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http://ﬂic.kr/p/dYor95
Adding Eventing

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54
gem install simple_events
http://github.com/jasonrclark/simple_events

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55
class SimpleEvents::Notifier
def initialize
@events = {}
...
end
end
simple_events

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56
...
def subscribe(event, &handler)
@events[event] ||= []
@events[event] << handler
check_for_runaway_subscriptions(event)
end
...
end
simple_events

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57
...
def notify(event, *args)
return unless @events.has_key?(event)
@events[event].each do |handler|
begin
handler.call(*args)
rescue => err
logger.debug("Fail #{@event}", err)
end
end
end
end
simple_events

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58
...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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59
...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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60
...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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61
...
begin
handler.call(*args)
rescue => err
end
end
end
end
simple_events

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ActiveSupport::
Notiﬁcations
http://ﬂic.kr/p/aWNwU2

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63
AS::Notifications
=
ActiveSupport::Notifications
activesupport

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Typical Rails Request
64
• action_dispatch.request
• start_processing.action_controller
• process_action.action_controller
• sql.active_record
• render_template.action_view
• ... and more!

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65
events = []
AS::Notifications.subscribe("event") do |*args|
events << *args
end
["render_template.action_view",
"e2a1e92a3c613576c2b0"
{:identifier=>"/file/path/here"}]
activesupport

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66
e = AS::Notifications::Event.new(*args)
e.name # => "render_template..."
e.duration # => 10 (in milliseconds)
e.payload # => { :identifier => ... }
activesupport

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67
AS::Notifications.instrument("evt", :data => 1)
activesupport

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68
AS::Notifications.instrument("evt", :data => 1) do
# your timed code here
end
activesupport

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• Regexp on Notifications.subscribe
• Event#parent_of?
• Temporary subscription
• Unsubscribe
• LogSubscriber
69
activesupport

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Where Are We Going?
The Pattern
Coupling
Mechanics
Responsibilities
70

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http://ﬂic.kr/p/a1dEec
Notiﬁers

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Naming
72

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Flexible Payload
73

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Primitives at
Boundaries
74

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75
http://ﬂic.kr/p/8w9PyF
Subscribers

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Who subscribes?
76

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77

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78
class UserSignup < Mutations::Command
def execute
user = User.create!(inputs)
NewsletterSubscriptions.create(user.id)
UserMailer.async(:deliver_welcome, user.id)
user
end
end

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79
Nesting

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Synchronous
80

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81
class SomeSubscriber
def initialize
events.subscribe(:configured) do
log_config
end
end
def log_config
...
end
end
Leaks

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Where Are We Going?
The Pattern
Coupling
Mechanics
Responsibilities
82

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The Pattern
Coupling
Mechanics
Responsibilities
?
Jason Clark
@jasonrclark
Ruby Agent Engineer

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Make an Event of It!

Make an Event of It!

Jason R Clark

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