Concurrency for !Dummies (Who Don't Get It (...Yet))

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CONCURRENCY FOR !DUMMIES (WHO DON’T GET IT(YET)) Monday, May 12, 14

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CONCURRENCY FOR !DUMMIES (WHO DON’T GET IT(YET)) Monday, May 12, 14

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NIRD.US Monday, May 12, 14

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ADA DEVELOPERS ACADEMY Monday, May 12, 14

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TYPICAL RESULT OF STUDYING CONCURRENCY Monday, May 12, 14

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• Ruby is bad at it • You don't need it • “HOLY S#!@ YOU HAVE TO DO THIS NOW!” • “HOLY S#!@ YOU GUYS DON'T SHARE STATE!” CONCURRENCY - WHAT HAVE YOU HEARD? Monday, May 12, 14

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1 WHAT IS CONCURRENCY? Monday, May 12, 14

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...I GUESS? Monday, May 12, 14

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• roast turkey • cornbread stuffing • mashed potatoes & sweet potatoes • fresh baked pies • cooked cranberry relish • gravy made from the roast turkey drippings AMERICAN THANKSGIVING MENU Monday, May 12, 14

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• Conﬂicting needs - multiple temperatures • Battling for a limited resource -- the one oven, the cooking range, or serving bowls • The need to interact with other dishes -- by arriving at the table at the same time, or because a side effect is an ingredient in another dish AMERICAN THANKSGIVING MENU Monday, May 12, 14

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“CONCURRENCY != PARALLELISM” - EVERYONE WHO TALKS ABOUT CONCURRENCY Monday, May 12, 14

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“CONCURRENCY IS ABOUT DEALING WITH LOTS OF THINGS AT ONCE. PARALLELISM IS ABOUT DOING LOTS OF THINGS AT ONCE.” -- ROB PIKE Monday, May 12, 14

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2 CONCURRENCY ACCORDING TO RUBY Monday, May 12, 14

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Process 1 Process 2 Process 3 Process 1 Thread 1 Thread 2 Thread 3 Thread 4 Monday, May 12, 14

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Green Threads Global Interpreter Lock Ruby Interpreter (MRI) Kernel OS Thread Monday, May 12, 14

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GLOBAL INTERPRETER LOCK (A.K.A. “THE GIL”) Monday, May 12, 14

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def neverending_method i = 0 while i = rand(10) + i end end thread_0 = Thread.new{ neverending_method } thread_1 = Thread.new{ neverending_method } thread_2 = Thread.new{ neverending_method } thread_0.join Monday, May 12, 14

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Green Threads Global Interpreter Lock Ruby Interpreter (MRI) Kernel OS Threads Monday, May 12, 14

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require 'benchmark' Benchmark.bm do |b| b.report('Sequential:') do 2.times do sleep(1) end end b.report('Threaded:') do a = Thread.new{ sleep(1) } b = Thread.new{ sleep(1) } a.join b.join end end Monday, May 12, 14

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require 'benchmark' Benchmark.bm do |b| b.report('Sequential:') do 10_000.times { 1 * 1 } end b.report('Threaded:') do a = Thread.new{ 5_000.times { 1 * 1 } } b = Thread.new{ 5_000.times { 1 * 1 } } a.join b.join end end Monday, May 12, 14

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sum = 0 threads = 10.times.map do Thread.new do 100_000.times do new_value = sum + 1 print "#{new_value} " if new_value % 250_000 == 0 sum = new_value end end end threads.each(&:join) puts "\nsum = #{sum}" Monday, May 12, 14

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sum = 0 mutex = Mutex.new threads = 10.times.map do Thread.new do mutex.synchronize do 100_000.times do new_value = sum + 1 print "#{new_value} " if new_value % 250_000 == 0 sum = new_value end end end end threads.each(&:join) puts "\nsum = #{sum}" Monday, May 12, 14

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CLOJURE AGENTS & FUTURES SCALA ACTORS ERLANG ACTORS, SUPERVISORS, & GEN_SERVER RUBY THREADS & MUTEXES Monday, May 12, 14

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“I WOULD REMOVE THE THREAD AND ADD ACTORS OR SOME OTHER MORE ADVANCED CONCURRENCY FEATURES” - MATZ Monday, May 12, 14

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ACTORS Monday, May 12, 14

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“DON’T COMMUNICATE BY SHARING STATE; SHARE STATE BY COMMUNICATING” Monday, May 12, 14

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REACTORS Monday, May 12, 14

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"WHICH IS BETTER, EMBER.JS OR ANGULAR?" Monday, May 12, 14

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"WHICH IS BETTER, EMBER.JS OR ANGULAR? IF YOU LIKE EMBER, GO READ THESE THREE BLOGS, BUT IF YOU LIKE ANGULAR, BUILD ME A WEBSITE." Monday, May 12, 14

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CHANNELS Monday, May 12, 14

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4 SO NOW WHAT? Monday, May 12, 14

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TALK.JOIN • Concurrency can melt your brain • It behaves differently than you expect • It requires a different way of thinking • It needs new patterns and abstractions Monday, May 12, 14

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HERE THERE BE DRAGONS • ~90% of Rubyists are building web apps • 80% of the time, concurrency isn’t the lowest hanging fruit • Its easy to overestimate the benefit, and underestimate the cost Monday, May 12, 14

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IT IS EASY TO FEEL LIKE THIS Monday, May 12, 14

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DON’T! GO WRITE SOME CODE INSTEAD! • Not knowing what you’re doing is no excuse • Start experimenting • Change your perspective and gain 80 IQ • Get started • Make a mess Monday, May 12, 14

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RESOURCES • “Seven Concurrency Patterns in Seven Weeks” by Paul Butcher • jdantonio/concurrent-ruby -- Modern concurrency tools for Ruby. Inspired by Erlang, Clojure, Scala, Haskell, F#, C#, Java, and classic concurrency patterns. • “Go For Rubyists” by Trevor Bramble • 'Concurrency Is Not Parallelism (It's Better)’ by Rob Pike Monday, May 12, 14

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KERRI MILLER (@KERRIZOR) • glass artist • Vespa mechanic • lighting designer • author & teacher • player of games • software developer Monday, May 12, 14