lighting tour of eventmachines basic structures

1. EventMachine
EM.run{ awesome_stuff! }
Christopher Spring

2. @autonomous

5. EventMachine

6. EventMachine

7. • Mostly IO bound
• Handle thousands
concurrent connections
• Stream data
• Real time data delivery
• You’ve got Mad Ruby Skills

8. What is EventMachine?
• Toolkit for creating evented applications
• Implementation of the Reactor Pattern
• MRI,YARV, jRuby, Rubinius

9. Evented?

10. Evented?
puts(1)
puts(2)
puts(3)

11. Evented?
puts(1)
puts(2)
puts(3)
puts(1)
work{ puts(3) }
puts(2)

12. Reactor pattern
“Event handling pattern for handling service
requests delivered concurrently to a service
handler by one or more inputs. The service
handler then demultiplexes the incoming
requests and dispatches them synchronously
to the associated request handlers.”
http://en.wikipedia.org/wiki/Reactor_pattern

13. Http Keyboard Udp etc
Service handler
Demultiplexer
Event dispatcher
Event Handler A
Event Handler B
Event Handler C
Event Handler D

14. Http Keyboard Udp etc
Service handler
Demultiplexer
Event dispatcher
Event Handler A
Event Handler B
Event Handler C
Event Handler D

15. Http Keyboard Udp etc
Service handler
Demultiplexer
Event dispatcher
Thread 1
Event Handler A Thread 2
Event Handler B
...
Event Handler C
Event Handler D Thread 20

16. Benefits
• Application code separate from reactor
• Non blocking IO
• Single process
• No threads!

17. Limitations
• Demultiplexing limits
• Some others we’ll cover later...

18. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

19. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

20. require "rubygems"
require "eventmachine"
EM.run do
# ...
EM.stop
end

21. ... don’t do this!
• big ass loops
• 1_000_000.times{}
• while condition?
• sleep
• blocking IO

22. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

23. class EchoServer < EM::Connection
def post_init
puts "New connection"
end
def unbind
puts "Connection closed"
end
def receive_data(data)
send_data ">> #{data}"
end
end
EM.run do
EM.start_server('127.0.0.1', 9000, EchoServer)
puts "Started server at 127.0.0.1:9000"
end

24. class EchoServer < EM::Connection
def post_init
puts "New connection"
end
def unbind
puts "Connection closed" # $ telnet localhost 9000
end # Hello
# >> Hello
def receive_data(data) # Bye
send_data ">> #{data}" # >> Bye
end
end
EM.run do
EM.start_server('127.0.0.1', 9000, EchoServer)
puts "Started server at 127.0.0.1:9000"
end

25. # TCP
EM.run do
EM.start_server('127.0.0.1', 9000, EchoServer)
end
# UDP
EM.run do
EM.open_datagram_socket('127.0.0.1', 9000, EchoServer)
end
# Unix-domain server
EM.run do
EM.start_unix_domain_server('/tmp/sock', nil, EchoServer)
end

26. class EchoClient < EM::Connection
def post_init
puts "Sending stuff to server"
send_data("Why, hello there!")
end
def unbind
puts "Connection closed"
end
def receive_data(data)
puts ">> #{data}"
end
end
EM.run do
EM.connect('127.0.0.1', 9000, EchoClient)
end

27. class EchoClient < EM::Connection
def post_init
puts "Sending stuff to server"
send_data("Why, hello there!")
end
def unbind
puts "Connection closed"
end
def receive_data(data)
puts ">> #{data}"
end
end
EM.run do
EM.connect('127.0.0.1', 9000, EchoClient)
end

28. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

29. EM.run do
EM.next_tick do
# ... awesome stuff
end
end

30. Task 1
Task 2
Task 3

31. Task 1
Task 2
Task 3
EM.run{ }

32. Task 1
Task 2
Task 3
EM.run{ }
EM.next_tick{ }

33. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

34. EM.run do
EM.defer do
send_email( user1 )
end
EM.defer do
send_email( user2 )
end
EM.defer do
send_email( user3 )
end
end

35. Email 1
Email 2
Email 3

36. Email 1
Email 2
Email 3
EM.defer{ }

37. EM.run do
get_stuff = Proc.new do
# ...
long_running_io()
end
use_stuff = Proc.new do |io_results|
# ...
end
# ...
EM.defer( get_stuff, use_stuff )
end

38. Teh Basics
• EM.run
• EM.connection
• next_tick; add_timer; add_periodic_timer
• EM.defer
• EM::Queue
• EM::Channel

39. EM.run do
queue = EM::Queue.new
# ...
queue.push( data1, data2 )
# ...
queue.pop { |data| puts data } # >> data1
end

40. EM.run do
queue = EM::Queue.new
EM.defer do
sleep( 2 )
queue.push( 'some@email.com' )
sleep( 3 )
queue.push( 'some@one.com')
end
welcomer = Proc.new do |email|
send_welcome( email )
EM.next_tick( queue.pop(&welcomer) )
end
queue.pop(&welcomer);
end

41. Teh Basics
• EM.run
• EM.connection
• EM.next_tick
• EM.defer
• EM::Queue
• EM::Channel

42. EM.run do
channel = EM::Channel.new
EM.defer do
channel.subscribe do |msg|
puts "Received #{msg}"
end
end
EM.add_periodic_timer(1) do
channel << Time.now
end
end

43. Deferrable
• Light weight concurrency
• Delayed execution with triggers
• :succeeded
• :failed
• nil
• callback and errback

44. class LoanRequest
include EM::Deferrable
def initialize( name )
@name = name
callback do |who|
puts "Approved #{who}!"
end
errback do |who|
puts "Denied #{who}!"
end
end
def approved!
# succeed( *args )
set_deferred_status(:succeeded, @name)
end
def denied!
# fail( *args )
set_deferred_status(:failed, @name)
end
end

45. class LoanRequest
include EM::Deferrable
def initialize( name )
@name = name
callback do |who| EM.run do
puts "Approved #{who}!" s1 = LoanRequest.new('Marc')
end s1.approved!
errback do |who| s2 = LoanRequest.new('Chris')
puts "Denied #{who}!" EM.add_timer(2){ s2.denied! }
end end
end
def approved!
# succeed( *args )
set_deferred_status(:succeeded, @name)
end
def denied!
# fail( *args )
set_deferred_status(:failed, @name)
end
end

46. class LoanRequest
include EM::Deferrable
def initialize( name )
@name = name
callback do |who| EM.run do
puts "Approved #{who}!" s1 = LoanRequest.new('Marc')
end s1.approved!
errback do |who| s2 = LoanRequest.new('Chris')
puts "Denied #{who}!" EM.add_timer(2){ s2.denied! }
end end
end
def approved!
# succeed( *args )
set_deferred_status(:succeeded, @name)
end # :00 Approved Marc!
# :02 Denied Chris!
def denied!
# fail( *args )
set_deferred_status(:failed, @name)
end
end

47. state: nil

48. state: nil
callback{}
callback{}
callback{}

49. state: nil
callback{} errback{}
callback{} errback{}
callback{}

50. state: succeeded
callback{} errback{}
callback{} errback{}
callback{}

51. state: succeeded
callback{}
callback{}
callback{}

52. state: succeeded

53. state: failed
callback{} errback{}
callback{} errback{}
callback{}

54. state: failed
errback{}
errback{}

55. state: failed

56. class Mailer
include EM::Deferrable
def add_mailing(val)
callback do
sleep 1
puts "Sent #{val}"
end
end
def connection_open!
puts 'Open connection'
succeed
end
def connection_lost!
puts 'Lost connection'
set_deferred_status nil
end
end

57. EM.run do
m = Mailer.new
class Mailer
m.add_mailing(1)
include EM::Deferrable
m.add_mailing(2)
m.connection_open!
def add_mailing(val)
callback do
EM.add_timer(1) do
sleep 1
m.connection_lost!
puts "Sent #{val}"
EM.add_timer(2) do
end
m.add_mailing(3)
end
m.add_mailing(4)
m.connection_open!
def connection_open!
end
puts 'Open connection'
end
succeed
end
end
def connection_lost!
puts 'Lost connection'
set_deferred_status nil
end
end

58. EM.run do
m = Mailer.new
class Mailer
m.add_mailing(1)
include EM::Deferrable
m.add_mailing(2)
m.connection_open!
def add_mailing(val)
callback do
EM.add_timer(1) do
sleep 1
m.connection_lost!
puts "Sent #{val}"
EM.add_timer(2) do
end
m.add_mailing(3)
end
m.add_mailing(4)
m.connection_open!
def connection_open!
end
puts 'Open connection'
end
succeed
end
end
def connection_lost! # Open connection
puts 'Lost connection' # Sent 1
set_deferred_status nil # Sent 2
end # Lost connection
end # Open connection
# Sent 3
# Sent 4

59. Gotchas
• Inverted flow of control can make
debugging difficult
• Synchronous code will slow it down
• Use/Write libraries for EM

60. Worth checking out
• EM-Synchrony:
https://github.com/igrigorik/em-synchrony
• Goliath:
https://github.com/postrank-labs/goliath
• Async_Sinatra:
https://github.com/raggi/async_sinatra

62. Baie Dankie!

63. Questions?