Mike Subelsky presents the basics of Ruby's various concurrency models

1. Ruby Concurrency
Slides & links posted to

2. Goal = Efficiency

3. At the Expense of

4. What Is Inefficient?
CPU Idling While You

5. What Is Inefficient?
Not Using All of Your

6. Types of Ruby
•Processes
•Threads
•Actors
•Fibers
•Events

7. Completely
Hadoop

8. Completely
Hadoop

9. Forked Processes
http://tomayko.com/writings/unicorn-is-unix
Ruby subprocess

10. Forked Processes
http://tomayko.com/writings/unicorn-is-unix
Ruby subprocess

11. forkoff gem

12. Many Ways to Start
system, exec, IO.popen,

13. Complex Fork
Spork, Unicorn,

14. Copy-on-Write
Rubinius, Enterprise

15. Copy-on-Write
Rubinius, Enterprise

16. Process Concurrency
•Simple
•Easy to debug

17. Process Concurrency
•Requires you to start/monitor each process
•Requires some type of RPC (dRb, Resque, etc)
•Can’t share resources (like connection pools)
•Memory inefficient w/o copy-on-write
•One process per core

18. Thread Concurrency
http://blog.carbonfive.com/2011/10/11/a-modern-guide-to-threads/
Concurrency within a

19. Thread Concurrency
http://blog.carbonfive.com/2011/10/11/a-modern-guide-to-threads/
Concurrency within a

20. Concurrent vs Parallel

21. Concurrent vs Parallel

22. Simple Thread Example

23. Complex Thread
Mongrel

24. Green Threads
•VM-managed
•Lightweight
•1 per core
•Blocking I/O blocks all threads

25. Native Threads
•Scheduled by OS
•Do not block other threads during I/O
•Can run on multiple cores*

26. *Global Interpreter Lock
•Only allows one thread to run at a time
•Ruby C code not threadsafe
•Released during I/O

27. Released During I/O
http://yehudakatz.com/2010/08/14/threads-in-ruby-enough-already/

28. Rubies without GIL
http://www.engineyard.com/blog/2011/ruby-concurrency-and-you/

29. Thread Safety
http://blog.carbonfive.com/2011/10/11/a-modern-guide-to-threads/

30. Thread Safety
http://blog.carbonfive.com/2011/10/11/a-modern-guide-to-threads/

31. Thread Safety
ruby thread.rb = 200000
jruby thread.rb = 1067198
http://blog.carbonfive.com/2011/10/11/a-modern-guide-to-threads/

32. Thread Safety

33. Thread Safety
Queue, SizedQueue,

34. Thread Pros
•More intuitive than fibers/events
•Sans GIL: most efficient/performant* technique
•Single process to monitor
•Shared resources, no RPC
•Fine-grained control of thread lifecycle
*http://teddziuba.com/2011/10/straight-talk-on-event-loops.html

35. Thread Cons
•Increased complexity (vs processes)
•Notoriously hard to debug
•Potential for deadlocks and race conditions
Text

36. Actor Concurrency
Message passing vs.

37. Actor Concurrency
Message passing vs.

38. Actor Concurrency
“Threads that don’t

39. Actor Concurrency
http://mperham.github.com/girl_friday/
girl_friday

40. Where You Can Get
•JRuby and Rubinius Actor API
•celluloid gem
Text

41. Fiber Concurrency
Manually scheduled

42. Fiber Concurrency
•Code blocks that can be paused/resumed
•Lighter than threads, cannot be preempted
•Scheduled by programmer
•Can share data without mutexes
Manually scheduled

43. Simple Fiber Example
http://paulbarry.com/articles/2010/04/01/fibers-in-ruby-1-9

44. Complex Fiber Example
Goliath, em-synchrony,

45. Complex Fiber Example
Goliath, em-synchrony,

46. Fiber Pros
•Much lighter memory use than threads
•Faster to start vs threads
•Can share data without mutex
•Can simplify asynchronous APIs (em-synchrony)
Text

47. Fiber Cons
•Limited to one CPU core
•Nonintuitive
•Syntax can get confusing
•Need to use fiber-aware libraries for I/O
Text

48. Event Concurrency
Single-thread w/

49. Event Concurrency
Single-thread w/

50. EM::WebSocket

51. EventMachine Pros
•Performs well under heavy network I/O
•Zero overhead
•Can still use threads via EM.defer

52. EventMachine Cons
•Inversion of control can be confusing
•Hard to test
•Nested callbacks can lead to spaghetti code
•Threads can still beat events (all apps will
eventually become CPU bound)

53. General Advice: MRI
Threads/Actors
Threads/Actors
Events Threads/Actors
Forks/Processes
Fibers (synchrony)

54. General Advice: JRuby/
Threads/Actors
Threads/Actors Threads/Actors
Events

55. Links on subelsky.com
Questions?
@subelsky