Concurrent systems in Ruby

Slides from my talk at RailsClub.

For the longest time, Ruby has been criticized for its underwhelming concurrency story, but things have changed, Ruby has changed.
In this talk I will showcase a few different options for concurrency, including the classic mutex/condition variable combo, Node style evented IO, Clojure-style compare-and-set, and Erlang-style actors. I will show you how you can use each of these in Ruby, and how Ruby gives you more choice than most other platforms when it comes to concurrency.

I will give you an introduction to Celluloid, the premiere framework for building concurrent applications in Ruby, showing you how it really works and how it combines the best of all options into one cohesive solution.

Transcript

1. Concurrent systems in Ruby Jonas Nicklas, Elabs
3. What is concurrency?
4. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. ! Aliquam nec neque magna. Vestibulum sit amet sollicitudin arcu, eget viverra magna. Duis pharetra ullamcorper ipsum, eu convallis odio ultrices eget. Praesent pulvinar lorem felis, in tristique tellus volutpat posuere. Donec porttitor turpis sit amet eros lacinia fermentum in nec turpis. Duis id sagittis turpis, sed accumsan est. Vestibulum tincidunt sit amet eros quis sagittis. Vivamus sit amet felis ut est varius ornare id sed leo. Donec at metus mi. Vivamus euismod purus quis sem tristique maximus. ! Phasellus commodo purus vel ipsum porttitor, in ultrices ante aliquam. Donec tempor mi quis nunc condimentum varius. Curabitur euismod sagittis porta. Maecenas fringilla, lectus ut laoreet euismod, enim erat rhoncus orci, vitae lobortis nibh eros volutpat odio. Morbi ac mauris eu arcu viverra placerat. Vestibulum eget ex euismod, faucibus velit sit amet, luctus ligula. Vivamus massa tortor, fringilla vitae neque nec, aliquam consequat nulla. Integer pellentesque viverra tristique. Nunc varius semper aliquet. Proin quis sagittis neque, quis tristique justo. ! Integer neque tellus, fermentum in purus vel, euismod blandit metus. In ac dolor sit amet est sodales ultrices. Sed quis nisl nec lacus porttitor lobortis quis tincidunt massa. Suspendisse accumsan enim diam, ut tincidunt augue placerat et. Curabitur faucibus, orci vitae hendrerit cursus, lectus leo vulputate tellus, hendrerit pulvinar ex lorem eget augue. Praesent sagittis sodales volutpat. Aenean tempus velit commodo quam iaculis, vel condimentum nunc ultrices. Phasellus eget nisi nec leo consectetur accumsan. Curabitur dignissim placerat purus vel euismod. Vestibulum luctus vel neque eu suscipit. Nulla eget neque ipsum. Suspendisse id mauris sit amet mauris faucibus ornare. Integer commodo placerat lacinia. Sed sollicitudin risus a nisl sagittis aliquet. Suspendisse at quam ipsum. Sed augue ligula, maximus nec blandit ut, bibendum quis nibh. ! Phasellus in commodo massa. Donec tincidunt, tellus ut condimentum aliquet, orci odio elementum justo, a tempus purus quam eget sem. Cras commodo justo arcu, non efficitur orci luctus nec. Ut sit amet varius libero. Suspendisse quis nibh vel tellus auctor tempus. Vestibulum sagittis felis pellentesque neque eleifend, quis pellentesque purus ornare. Sed finibus libero id malesuada tempor. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. ! Aliquam nec neque magna. Vestibulum sit amet sollicitudin arcu, eget viverra magna. Duis pharetra ullamcorper ipsum, eu convallis odio ultrices eget. Praesent pulvinar lorem felis, in tristique tellus volutpat posuere. Donec porttitor turpis sit amet eros lacinia fermentum in nec turpis. Duis id sagittis turpis, sed accumsan est. Vestibulum tincidunt sit amet eros quis sagittis. Vivamus sit amet felis ut est varius ornare id sed leo. Donec at metus mi. Vivamus euismod purus quis sem tristique maximus. ! Phasellus commodo purus vel ipsum porttitor, in ultrices ante aliquam. Donec tempor mi quis nunc condimentum varius. Curabitur euismod sagittis porta. Maecenas fringilla, lectus ut laoreet euismod, enim erat rhoncus orci, vitae lobortis nibh eros volutpat odio. Morbi ac mauris eu arcu viverra placerat. Vestibulum eget ex euismod, faucibus velit sit amet, luctus ligula. Vivamus massa tortor, fringilla vitae neque nec, aliquam consequat nulla. Integer pellentesque viverra tristique. Nunc varius semper aliquet. Proin quis sagittis neque, quis tristique justo. ! Integer neque tellus, fermentum in purus vel, euismod blandit metus. In ac dolor sit amet est sodales ultrices. Sed quis nisl nec lacus porttitor lobortis quis tincidunt massa. Suspendisse accumsan enim diam, ut tincidunt augue placerat et. Curabitur faucibus, orci vitae hendrerit cursus, lectus leo vulputate tellus, hendrerit pulvinar ex lorem eget augue. Praesent sagittis sodales volutpat. Aenean tempus velit commodo quam iaculis, vel condimentum nunc ultrices. Phasellus eget nisi nec leo consectetur accumsan. Curabitur dignissim placerat purus vel euismod. Vestibulum luctus vel neque eu suscipit. Nulla eget neque ipsum. Suspendisse id mauris sit amet mauris faucibus ornare. Integer commodo placerat lacinia. Sed sollicitudin risus a nisl sagittis aliquet. Suspendisse at quam ipsum. Sed augue ligula, maximus nec blandit ut, bibendum quis nibh. ! Phasellus in commodo massa. Donec tincidunt, tellus ut condimentum aliquet, orci odio elementum justo, a tempus purus quam eget sem. Cras commodo justo arcu, non efficitur orci luctus nec. Ut sit amet varius libero. Suspendisse quis nibh vel tellus auctor tempus. Vestibulum sagittis felis pellentesque neque eleifend, quis pellentesque purus ornare. Sed finibus libero id malesuada tempor.
5. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam.
6. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam.
7. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. ! Aliquam nec neque magna. Vestibulum sit amet sollicitudin arcu, eget viverra magna. Duis pharetra ullamcorper ipsum, eu convallis odio ultrices eget. Praesent pulvinar lorem felis, in tristique tellus volutpat posuere. Donec porttitor turpis sit amet eros lacinia fermentum in nec turpis. Duis id sagittis turpis, sed accumsan est. Vestibulum tincidunt sit amet eros quis sagittis. Vivamus sit amet felis ut est varius ornare id sed leo. Donec at metus mi. Vivamus euismod purus quis sem tristique maximus. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. Concurrency Switching between multiple tasks
8. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc ut lorem id nulla efficitur bibendum tempus rutrum velit. Aenean sagittis pretium porttitor. Praesent blandit, ex in gravida feugiat, felis leo consectetur nulla, quis fermentum nunc leo id metus. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum sed iaculis purus, ut tristique velit. Maecenas consectetur rhoncus nisi, quis sollicitudin enim rhoncus eget. Duis in ex in metus ullamcorper euismod. Integer nulla est, maximus quis dapibus a, fermentum a lorem. Fusce ut ullamcorper lorem. Proin tempus interdum sodales. Aenean sed arcu iaculis, imperdiet lacus sed, faucibus diam. Parallelism Performing multiple tasks at the same time
9. Single CPU Concurrent but not Parallel
10. We can have Concurrency without Parallelism
11. Ruby MRI GIL (Global Interpreter Lock) prevents parallelism (but not concurrency)
12. JRuby and Rubinius no GIL Concurrent and Parallel
13. Switch between tasks
14. the Scheduler
15. Time Scheduler Alternative 1
16. Time Task A I’m done! Scheduler Alternative 1
17. Time Task A Task B I’m done! Scheduler Alternative 1
18. Time Task A Task B Task A Scheduler I’m done! Alternative 1
19. co-operative multitasking
20. Time Scheduler Problem
21. Run Task A! Time Task A LOL!!! Scheduler Problem
22. Time Scheduler Alternative 2
23. Time Task A Scheduler ZAP! Alternative 2
24. Time Task A Task B Scheduler ZAP! Alternative 2
25. Time Task A Task B Task A Scheduler ZAP! Alternative 2
26. pre-emptive multitasking
27. unpredictable Context-switches
28. Our code can be suspended at any point in time (in a pre-emptively scheduled system)
29. Processes isolated memory Task A Task B
30. Task A Task B (possibly) shared memory shared Threads
31. What is a thread?
32. duplicated memory duplicated duplicated Processes Task A Task B
33. x = x + 1
34. x = 0 ! 100.times.map do Thread.new do x = x + 1 end end.each(&:join) ! puts x
35. read value increase value write value back
36. Thread A Thread B Integer value read value ← 0 increase value 0 write back → 1 read value ← 1 increase value 1 write back → 2 source: wikipedia.org
37. Thread A Thread B Integer value read value ← 0 read value ← 0 increase value 0 increase value 0 write back → 1 write back → 1 source: wikipedia.org
38. Race-condition
39. Ruby doesn’t protect you
40. Don’t share mutable state
41. Celluloid Idiomatic Ruby code https://github.com/celluloid/celluloid
42. class Counter attr_reader :value ! def initialize @value = 0 end ! def increment @value += 1 end end
43. class Counter attr_reader :value ! def initialize @value = 0 end ! def increment @value += 1 end end
44. require "celluloid" ! class Counter include Celluloid ! attr_reader :value ! def initialize @value = 0 end ! def increment @value += 1 end end
45. Mutual Exclusion Lock a.k.a Mutex Pessimistic Lock
46. class Counter attr_reader :value ! def initialize @mutex = Mutex.new @value = 0 end ! def increment @mutex.synchronize do @value += 1 end end end
47. Atomic Optimistic Lock
48. class Counter attr_reader :value ! def initialize @value = Atomic.new(0) end ! def increment @value.update do |x| x + 1 end end end
49. Atoms + Persistent datastructures = ♥ (Clojure style concurrency)
50. Hamster https://github.com/hamstergem/hamster Atomic https://github.com/ruby-concurrency/atomic Concurrent Ruby https://github.com/ruby-concurrency/concurrent-ruby
51. Green vs Native
52. Node.js Green Threads
53. Node.js collaboratively scheduled not parallel* * ignoring workers
54. var x = 0; ! x = x + 1; // safe ! setTimeout(function() { // context switch here x = x + 1; // safe }, 100); ! setTimeout(function() { // context switch here x = x + 1; // safe }, 100);
55. Compromise
56. Erlang Cheap Green Threads
57. Ruby 1.8 Green Threads (they sucked)
58. Ruby 1.9+ Native Threads (yay!)
59. Ruby 1.9+ Fibers
60. Manual control co-operative scheduling
61. Fibers are “lightweight” (but it comes at a price)
62. Tasks need Stacks
63. Fibers have small stacks
64. Rails + Fibers = :(
65. UNIX Processes
66. Multiple UNIX Processes e.g. Passenger or Unicorn
67. Rails (Processes) Server Process Process Process Process Requests application code request specific data application code request specific data
68. Rails (threads) Server Thread Thread Thread Thread Requests application code request specific data
69. Rails (copy-on-write) Server Process Process Process Process Requests application code request specific data
70. Platform Parallel Multitasking Scheduler Memory Isolation Ruby Threads (MRI 1.8) no pre-emptive green no Ruby Threads (MRI 1.9+) no pre-emptive native no Ruby Threads (JRuby, Rubinius) yes pre-emptive native no Ruby Fibers no collaborative green no Node.js no collaborative green no Erlang yes pre-emptive green yes UNIX processes (e.g. Unicorn) yes pre-emptive native yes Go (Goroutines) yes pre-emptive green no Clojure yes pre-emptive native immutable
71. Celluloid
72. require "celluloid" ! class Counter include Celluloid ! attr_reader :value ! def initialize @value = 0 end ! def increment @value += 1 end end
73. Each Instance has its own pre-emptively scheduled Native Thread
74. >> counter = Counter.new => #<Celluloid::CellProxy(Counter:0x48a8) @value=0> >> counter.thread => #<Celluloid::ThreadHandle:0x48dc @mutex=#<Mutex:0x48e0 @owner=nil> @thread=#<Celluloid::Thread:0x48e8 id=8 sleep> @join=#<ConditionVariable:0x48ec @waiters=[]>>
75. Each Actor has its own Collaborative Scheduler
76. Each method call to an Actor Has its own (collaboratively scheduled) Task
77. Celluloid calls context-switches “pipelining”
78. Celluloid pipelines if…. 1. Making a synchronous call from one actor to another 2. Any I/O operations when using Celluloid::IO or Celluloid::ZMQ 3. Waiting for the result of a future 4. Sleeping using Celluloid#sleep 5. Waiting for a condition 6. Receiving a raw asynchronous message using the receive method source: https://github.com/celluloid/celluloid/wiki/Pipelining-and-execution-modes
79. Regular I/O blocks!
80. require "celluloid" ! class Counter include Celluloid ! attr_reader :value ! def initialize @other = OtherActor.new @value = 0 end ! def increment @other.some_method # context switch here @value += 1 end end
81. require "celluloid" ! class Counter include Celluloid ! attr_reader :value ! def initialize @other = link(Actor[:some_other_actor]) @value = 0 end ! exclusive :increment def increment @other.call_some_method # no context switch! @value += 1 end end
82. require "celluloid" ! class Counter include Celluloid ! attr_reader :value ! def initialize @other = OtherActor.new @value = 0 end ! def increment @other.some_method # context switch here @value += 1 end end
83. Errors
84. require "celluloid/autostart" ! class TimeBomb include Celluloid ! def initialize @count = 5 every(1) { ping } end ! def ping @count -= 1 raise "boom!" if @count == 0 puts "tick!" end end ! TimeBomb.supervise_as(:time_bomb)
85. $ ruby -r ./time_bomb.rb -e sleep tick! tick! tick! tick! E, [2014-09-25T20:16:12.436596 #26881] ERROR -- : Actor crashed! RuntimeError: boom! tick! tick! tick! tick! E, [2014-09-25T20:16:17.446067 #26881] ERROR -- : Actor crashed! RuntimeError: boom! tick! …
86. class RoadRunner include Celluloid ! def initialize @time_bomb = TimeBomb.new_link puts "MEEP" end end ! RoadRunner.supervise_as(:road_runner)
87. $ ruby -r ./road_runner.rb -e sleep MEEP tick! tick! tick! tick! E, [2014-09-25T20:23:04.201099 #26976] ERROR -- : Actor crashed! RuntimeError: boom! MEEP tick! tick! tick! tick! E, [2014-09-25T20:23:09.211179 #26976] ERROR -- : Actor crashed! RuntimeError: boom! MEEP tick! …
88. class RoadRunner include Celluloid ! trap_exit :ignore ! def initialize @time_bomb = TimeBomb.new_link puts "MEEP" end ! def ignore(actor, error) puts "Bomb exploded" end end ! RoadRunner.supervise_as(:road_runner)
89. $ ruby -r ./road_runner.rb -e sleep MEEP tick! tick! tick! tick! E, [2014-09-25T20:27:45.909766 #27045] ERROR -- : Actor crashed! RuntimeError: boom! Bomb exploded
90. class RoadRunner include Celluloid ! finalizer :death ! def initialize @time_bomb = TimeBomb.new_link puts "MEEP" end ! def death puts "Goodbye cruel world!" end end ! RoadRunner.supervise_as(:road_runner)
91. $ ruby -r ./road_runner.rb -e sleep MEEP tick! tick! tick! tick! E, [2014-09-25T20:35:23.649306 #27151] ERROR -- : Actor crashed! RuntimeError: boom! Goodbye cruel world! MEEP tick! tick!
92. Supervision Hierarchies
93. More!
94. Celluloid https://github.com/celluloid/celluloid Hamster https://github.com/hamstergem/hamster Atomic https://github.com/ruby-concurrency/atomic Concurrent Ruby https://github.com/ruby-concurrency/concurrent-ruby
97. THANKS! Jonas Nicklas, Elabs – @jonicklas