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A tale by @josevalim from @plataformatec CONCURRENCY LET’S TALK Friday, September 21, 2012

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Friday, September 21, 2012

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Core Team Member Friday, September 21, 2012

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Friday, September 21, 2012

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CONCURRENCY LET’S TALK Friday, September 21, 2012

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“Execute several tasks simultaneously” Friday, September 21, 2012

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Server Server Server Server Friday, September 21, 2012

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Server Friday, September 21, 2012

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MULTI CORE SINGLE PROCESS Friday, September 21, 2012

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state concurrency off off Friday, September 21, 2012

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The Declarative Model Because mathematics is awesome! Friday, September 21, 2012

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•no mutation •no concurrency •just functions Friday, September 21, 2012

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factorial = lambda do |x| case x when 0 1 else x * factorial.(x-1) end end print factorial.(10) # => 3628800 Friday, September 21, 2012

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Determinism Same input = > same output Friday, September 21, 2012

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•no i/o •no random •no side-effects •always returns the same result Friday, September 21, 2012

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lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012

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lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end a = 1 Friday, September 21, 2012

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lambda do |1, b| c = 42 d = also_expensive.(b) c + d end Friday, September 21, 2012

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lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012

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lambda do |a, b| d = also_expensive.(b) c = expensive_function.(a) c + d end Friday, September 21, 2012

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Haskell Using determinism for performance and expressiveness Friday, September 21, 2012

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l = lambda { |a,b,c| a + b + c } l.(1, 2, 3) #=> 6 l.curry #=> # l.curry.(1) #=> # l.curry.(1).(2).(3) #=> 6 Currying Friday, September 21, 2012

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l = lambda { |a,b| a * b } double = l.curry.(2) triple = l.curry.(3) Currying Friday, September 21, 2012

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sum a b c = a + b + c (sum 1 2 3) (((sum 1) 2) 3) Currying Friday, September 21, 2012

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x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Friday, September 21, 2012

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x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Compiler Friday, September 21, 2012

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x = expensive(1) y = expensive(3) z = (sum x) ((z 2) y) Compiler (sum expensive(1) 2 expensive(3)) Friday, September 21, 2012

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CONCURRENCY ON LET’S TURN Friday, September 21, 2012

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state concurrency off on Friday, September 21, 2012

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Dataflow variables Painless concurrency! Friday, September 21, 2012

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lambda do |a, b| c = expensive_function.(a) d = also_expensive.(b) c + d end Friday, September 21, 2012

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lambda do |a, b| thread { c = expensive_function.(a) } thread { d = also_expensive.(b) } c + d end Friday, September 21, 2012

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main Friday, September 21, 2012

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main spawn thread 1 Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 unbound c Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 unbound c defines c Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 unbound c defines c unbound d Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 unbound c defines c unbound d defines d Friday, September 21, 2012

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main spawn thread 1 spawn thread 2 unbound c defines c unbound d defines d c + d Friday, September 21, 2012

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STATE ON LET’S TURN Friday, September 21, 2012

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state concurrency on on Friday, September 21, 2012

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Friday, September 21, 2012

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PROBLEM THE Friday, September 21, 2012

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class Counter mattr_accessor :i self.i = 0 end thread { Counter.i = Counter.i + 1 } Friday, September 21, 2012

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thread 1 Counter.i thread 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 2 2 2 2 Friday, September 21, 2012

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•shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012

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•shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012

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class Counter mattr_accessor :i self.i = 0 end thread { Counter.i = Counter.i + 1 } Friday, September 21, 2012

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class Counter mattr_accessor :i self.i = 0 end thread { synchronize { Counter.i = Counter.i + 1 } } Friday, September 21, 2012

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thread 1 Counter.i thread 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 synchronize { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 1 synchronize { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 1 synchronize { 2 } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 2 1 synchronize { 2 } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 2 2 1 synchronize { 2 } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 2 3 2 1 synchronize { 2 } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 2 2 3 3 2 1 synchronize { 2 } Friday, September 21, 2012

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+most popular approach +explicit control over the lock Friday, September 21, 2012

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- explicit control over the lock - pessimistic approach Friday, September 21, 2012

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•shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012

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class Counter mattr_accessor :i self.i = ref { 0 } end thread { atomic { Counter.i = Counter.i + 1 } } Friday, September 21, 2012

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thread 1 Counter.i thread 2 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 1 atomic { } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 1 atomic { } Friday, September 21, 2012

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thread 1 Counter.i thread 2 0 1 0 1 1 1 1 2 2 2 2 2 1 atomic { } Friday, September 21, 2012

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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

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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

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+ optimistic approach + no deadlock or race conditions Friday, September 21, 2012

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- potential unnecessary retries - transaction overhead Friday, September 21, 2012

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•shared-memory concurrent model •locks •transactional memory •message-passing concurrent model Friday, September 21, 2012

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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

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thread { server <- :increment } Friday, September 21, 2012

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thread 1 server thread 2 Friday, September 21, 2012

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thread 1 server thread 2 0 Friday, September 21, 2012

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thread 1 server thread 2 0 :increment Friday, September 21, 2012

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thread 1 server thread 2 0 1 :increment Friday, September 21, 2012

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thread 1 server thread 2 0 1 :increment :increment Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 :increment :increment Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 :increment :increment :increment Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 3 :increment :increment :increment Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 3 :increment :increment :increment :check Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 3 3 :increment :increment :increment :check Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 3 3 :increment :increment :increment :check Friday, September 21, 2012

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thread 1 server thread 2 0 2 1 3 3 3 :increment :increment :increment :check Friday, September 21, 2012

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“Do not communicate by sharing memory; instead, share memory by communicating;” Effective Go Friday, September 21, 2012

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+no need for synchronization +easy to distribute (location transparency) Friday, September 21, 2012

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- coordination may be tricky - non-conventional approach Friday, September 21, 2012

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UP SUMMING Friday, September 21, 2012

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message-passing locks stm go, erlang ruby clojure dataflow oz Friday, September 21, 2012

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github.com/celluloid Friday, September 21, 2012

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@elixirlang / elixir-lang.org Friday, September 21, 2012

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MATTER DEFAULTS Friday, September 21, 2012

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Erlang and Clojure defaults to immutable Friday, September 21, 2012

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MAGIC BULLET THERE IS NO Friday, September 21, 2012

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REFERENCES Seven languages in seven weeks Friday, September 21, 2012

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REFERENCES Concepts, Techniques and Models of Computer Programming Friday, September 21, 2012

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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

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? QUESTIONS @josevalim Friday, September 21, 2012