Let's talk concurrency

For a long time, the de facto way of doing multi-core concurrency was using threads. However, the complexity of manipulating threads and state affected negatively how developers perceive concurrency. Fortunately, languages like Clojure and Erlang implement new paradigms that aim to make concurrency easier.

In this talk, José Valim is going to discuss the role state play in concurrency and introduce different paradigms for multi-core concurrency, like Actors and Software Transactional Memory, explaining their trade-offs and why they matter to us developers.

Transcript

1. A tale by @josevalim from @plataformatec CONCURRENCY LET’S TALK Friday, September 21, 2012
2. Friday, September 21, 2012
3. Core Team Member Friday, September 21, 2012
4. Friday, September 21, 2012
5. CONCURRENCY LET’S TALK Friday, September 21, 2012
6. “Execute several tasks simultaneously” Friday, September 21, 2012
7. Server Server Server Server Friday, September 21, 2012
8. Server Friday, September 21, 2012
9. MULTI CORE SINGLE PROCESS Friday, September 21, 2012
10. state concurrency off off Friday, September 21, 2012
11. The Declarative Model Because mathematics is awesome! Friday, September 21, 2012
12. •no mutation •no concurrency •just functions Friday, September 21, 2012
13. factorial = lambda do |x| case x when 0 1 else x * factorial.(x-1) end end print factorial.(10) # => 3628800 Friday, September 21, 2012
14. Determinism Same input = > same output Friday, September 21, 2012
15. •no i/o •no random •no side-effects •always returns the same result Friday, September 21, 2012
16. lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012
17. lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end a = 1 Friday, September 21, 2012
18. lambda do |1, b| c = 42 d = also_expensive.(b) c + d end Friday, September 21, 2012
19. lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012
20. lambda do |a, b| d = also_expensive.(b) c = expensive_function.(a) c + d end Friday, September 21, 2012
21. Haskell Using determinism for performance and expressiveness Friday, September 21, 2012
22. l = lambda { |a,b,c| a + b + c } l.(1, 2, 3) #=> 6 l.curry #=> #<Proc> l.curry.(1) #=> #<Proc> l.curry.(1).(2).(3) #=> 6 Currying Friday, September 21, 2012
23. l = lambda { |a,b| a * b } double = l.curry.(2) triple = l.curry.(3) Currying Friday, September 21, 2012
24. sum a b c = a + b + c (sum 1 2 3) (((sum 1) 2) 3) Currying Friday, September 21, 2012
25. x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Friday, September 21, 2012
26. x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Compiler Friday, September 21, 2012
27. x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Compiler (sum expensive(1) 2 expensive(3)) Friday, September 21, 2012
28. CONCURRENCY ON LET’S TURN Friday, September 21, 2012
29. state concurrency off on Friday, September 21, 2012
30. Dataflow variables Painless concurrency! Friday, September 21, 2012
31. lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012
32. lambda do |a, b| thread { c = expensive_function.(a) } thread { d = also_expensive.(b) } c + d end Friday, September 21, 2012
33. main Friday, September 21, 2012
34. main spawn thread 1 Friday, September 21, 2012
35. main spawn thread 1 spawn thread 2 Friday, September 21, 2012
36. main spawn thread 1 spawn thread 2 unbound c Friday, September 21, 2012
37. main spawn thread 1 spawn thread 2 unbound c defines c Friday, September 21, 2012
38. main spawn thread 1 spawn thread 2 unbound c defines c unbound d Friday, September 21, 2012
39. main spawn thread 1 spawn thread 2 unbound c defines c unbound d defines d Friday, September 21, 2012
40. main spawn thread 1 spawn thread 2 unbound c defines c unbound d defines d c + d Friday, September 21, 2012
41. STATE ON LET’S TURN Friday, September 21, 2012
42. state concurrency on on Friday, September 21, 2012
43. Friday, September 21, 2012
44. PROBLEM THE Friday, September 21, 2012
45. class Counter mattr_accessor :i self.i = 0 end thread { Counter.i = Counter.i + 1 } Friday, September 21, 2012
46. thread 1 Counter.i thread 2 Friday, September 21, 2012
47. thread 1 Counter.i thread 2 0 Friday, September 21, 2012
48. thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012
49. thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012
50. thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012
51. thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012
52. thread 1 Counter.i thread 2 0 1 0 1 1 1 Friday, September 21, 2012
53. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 Friday, September 21, 2012
54. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 Friday, September 21, 2012
55. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 Friday, September 21, 2012
56. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 Friday, September 21, 2012
57. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 2 Friday, September 21, 2012
58. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 2 2 Friday, September 21, 2012
59. •shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012
60. •shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012
61. class Counter mattr_accessor :i self.i = 0 end thread { Counter.i = Counter.i + 1 } Friday, September 21, 2012
62. class Counter mattr_accessor :i self.i = 0 end thread { synchronize { Counter.i = Counter.i + 1 } } Friday, September 21, 2012
63. thread 1 Counter.i thread 2 Friday, September 21, 2012
64. thread 1 Counter.i thread 2 0 Friday, September 21, 2012
65. thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012
66. thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012
67. thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012
68. thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012
69. thread 1 Counter.i thread 2 0 1 0 1 1 1 synchronize { Friday, September 21, 2012
70. thread 1 Counter.i thread 2 0 1 0 1 1 2 1 synchronize { Friday, September 21, 2012
71. thread 1 Counter.i thread 2 0 1 0 1 1 2 1 synchronize { 2 } Friday, September 21, 2012
72. thread 1 Counter.i thread 2 0 1 0 1 1 2 2 1 synchronize { 2 } Friday, September 21, 2012
73. thread 1 Counter.i thread 2 0 1 0 1 1 2 2 2 1 synchronize { 2 } Friday, September 21, 2012
74. thread 1 Counter.i thread 2 0 1 0 1 1 2 2 3 2 1 synchronize { 2 } Friday, September 21, 2012
75. thread 1 Counter.i thread 2 0 1 0 1 1 2 2 3 3 2 1 synchronize { 2 } Friday, September 21, 2012
76. +most popular approach +explicit control over the lock Friday, September 21, 2012
77. - explicit control over the lock - pessimistic approach Friday, September 21, 2012
78. •shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012
79. class Counter mattr_accessor :i self.i = ref { 0 } end thread { atomic { Counter.i = Counter.i + 1 } } Friday, September 21, 2012
80. thread 1 Counter.i thread 2 Friday, September 21, 2012
81. thread 1 Counter.i thread 2 0 Friday, September 21, 2012
82. thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012
83. thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012
84. thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012
85. thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012
86. thread 1 Counter.i thread 2 0 1 0 1 1 1 atomic { Friday, September 21, 2012
87. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 atomic { Friday, September 21, 2012
88. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 atomic { Friday, September 21, 2012
89. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 1 atomic { Friday, September 21, 2012
90. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 1 atomic { Friday, September 21, 2012
91. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { Friday, September 21, 2012
92. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012
93. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012
94. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012
95. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 1 atomic { } Friday, September 21, 2012
96. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 2 1 atomic { } Friday, September 21, 2012
97. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 2 3 1 atomic { } Friday, September 21, 2012
98. thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 2 3 3 1 atomic { } Friday, September 21, 2012
99. + optimistic approach + no deadlock or race conditions Friday, September 21, 2012
100. - potential unnecessary retries - transaction overhead Friday, September 21, 2012
101. •shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012
102. server = lambda do |i| receive when :increment server.(i+1) when :check client <- i server.(i) else warn "unknown message" server.(i) end end server.(0) Friday, September 21, 2012
103. thread { server <- :increment } Friday, September 21, 2012
104. thread 1 server thread 2 Friday, September 21, 2012
105. thread 1 server thread 2 0 Friday, September 21, 2012
106. thread 1 server thread 2 0 :increment Friday, September 21, 2012
107. thread 1 server thread 2 0 1 :increment Friday, September 21, 2012
108. thread 1 server thread 2 0 1 :increment :increment Friday, September 21, 2012
109. thread 1 server thread 2 0 2 1 :increment :increment Friday, September 21, 2012
110. thread 1 server thread 2 0 2 1 :increment :increment :increment Friday, September 21, 2012
111. thread 1 server thread 2 0 2 1 3 :increment :increment :increment Friday, September 21, 2012
112. thread 1 server thread 2 0 2 1 3 :increment :increment :increment :check Friday, September 21, 2012
113. thread 1 server thread 2 0 2 1 3 3 :increment :increment :increment :check Friday, September 21, 2012
114. thread 1 server thread 2 0 2 1 3 3 :increment :increment :increment :check Friday, September 21, 2012
115. thread 1 server thread 2 0 2 1 3 3 3 :increment :increment :increment :check Friday, September 21, 2012
116. “Do not communicate by sharing memory; instead, share memory by communicating;” Effective Go Friday, September 21, 2012
117. +no need for synchronization +easy to distribute (location transparency) Friday, September 21, 2012
118. - coordination may be tricky - non-conventional approach Friday, September 21, 2012
119. UP SUMMING Friday, September 21, 2012
120. message-passing locks stm go, erlang ruby clojure dataflow oz Friday, September 21, 2012
121. github.com/celluloid Friday, September 21, 2012
122. @elixirlang / elixir-lang.org Friday, September 21, 2012
123. MATTER DEFAULTS Friday, September 21, 2012
124. Erlang and Clojure defaults to immutable Friday, September 21, 2012
125. MAGIC BULLET THERE IS NO Friday, September 21, 2012
126. REFERENCES Seven languages in seven weeks Friday, September 21, 2012
127. REFERENCES Concepts, Techniques and Models of Computer Programming Friday, September 21, 2012
128. REFERENCES Software Transactional Memory http://java.ociweb.com/mark/stm/article.html Persistent Data Structures http://www.infoq.com/presentations/Value-Identity-State-Rich-Hickey Friday, September 21, 2012
129. ? QUESTIONS @josevalim Friday, September 21, 2012