GPars For Beginners

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The GPars (Groovy Parallel Systems) project provides multiple abstractions for concurrent, parallel programming in Groovy and Java. Rather than dealing directly with threads, synchronization, and locks, or even the java.util.concurrent classes added in Java 5, the project allows you to think in terms of actors, data flows, or composable asynchronous functions (to name a few).

In this talk, I covered the basics of GPars, including what it's like to learn to use it. Although I've done a fair amount of concurrent programming, I've just started using GPars. As such, this talk should be suitable for Groovy beginners.

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GPars For Beginners

  1. 1. For Beginners A Groovy approach to concurrent programmingMatt Passell May 25, 2011
  2. 2. About Me• Longtime Java developer (since 97)• Using Groovy on and off since early 2008• Concurrent programming enthusiast• Started software consultancy in 2007• More Groovy + Less Java = More Happy
  3. 3. Early History● October 2008: Václav Pech creates GParallelizer● September 2009: project renamed to GPars, moved to Codehaus, and Groovy luminaries join the team - (Dierk König, Paul King, Alex Tkachman, Russel Winder)
  4. 4. GPars Has a Logo Contest http://gpars.codehaus.org/Logo+Contest
  5. 5. History● October 2008: Václav Pech creates GParallelizer● September 2009: project renamed to GPars, moved to Codehaus, and Groovy luminaries join the team (Dierk König, Paul King, Alex Tkachman, Russel Winder)● December 2009: GPars gets a logo● May 2010: 0.10 Release● December 2010: 0.11 Release● May 2011: 0.12 Beta 1
  6. 6. What GPars Provides● Code-level Helpers● Architecture-level Concepts● Protecting Shared Mutable State
  7. 7. What GPars Provides● Code-level Helpers ● Fork/Join ● Map/Reduce (Parallel Collections) ● Asynchronous Processing* *not covered in this presentation
  8. 8. What GPars Provides● Architecture-level Concepts ● Dataflow Concurrency ● Actors ● Communicating Sequential Processes* *not covered in this presentation
  9. 9. What GPars Provides● Protecting Shared Mutable State ● Agents ● Software Transactional Memory* *not covered in this presentation
  10. 10. Recurring Patterns● Favor immutability● Stateless code blocks (similar to Servlets)
  11. 11. Fork/Join & Map/Reduce Fork Join Fork Join Map Map Reduce
  12. 12. Fork/Joindef list = [1, 2, 3, 4]GParsPool.withPool { assert [2, 4, 6, 8] == list.collectParallel { it * 2 } def animals = [dog, ant, cat, whale] println(animals.makeTransparent(). collect {it.toUpperCase()}. groupBy {it.contains A})}ParallelEnhancer.enhanceInstance(list)assert [2, 4, 6, 8] == list.collectParallel { it * 2 } DemoParallelizer & DemoParallelEnhancer.groovy
  13. 13. Fork/Joindef list = [1, 2, 3, 4]GParsPool.withPool { assert [2, 4, 6, 8] == list.collectParallel { it * 2 } def animals = [dog, ant, cat, whale] println(animals.makeTransparent(). collect {it.toUpperCase()}. groupBy {it.contains A})}ParallelEnhancer.enhanceInstance(list)assert [2, 4, 6, 8] == list.collectParallel { it * 2 } DemoParallelizer & DemoParallelEnhancer.groovy
  14. 14. Parallel Collections (Map/Reduce)GParsPool.withPool { assert 20 == [1, 2, 3, 4, 5].parallel. filter {it % 2 == 0}. map {it ** 2}. reduce {a, b -> a + b} //sum the squares of even numbers def urls = [http://www.jroller.com, http://www.dzone.com, http://www.infoq.com] println Sum of chars in all pages: + urls.parallel.map { it.toURL().text.size() }.sum()//The equivalent using Fork/Join// println urls.collectParallel { it.toURL().text.size() }.sum()} DemoMapReduce.groovy
  15. 15. Dataflow Concurrency● Modeled as a flow of data rather than a flow of execution● Tree of dependent values
  16. 16. Like this?
  17. 17. How about this?
  18. 18. My Last Try A B CD E D
  19. 19. When you put it that way... A B CE D
  20. 20. In Codedef flow = new DataFlows()task { flow.a = flow.b + flow.c }task { flow.b = flow.d + flow.e }task { flow.c = flow.d }task { flow.d = 17 }task { flow.e = 12 }assert 46 == flow.aprintln "flow.a = ${flow.a}"println "flow.b = ${flow.b}"
  21. 21. Actorsfinal def doubler = Actors.reactor { 2 * it}Actor actor = Actors.actor { (1..10).each {doubler << it} int i = 0 loop { i += 1 if (i > 10) stop() else { react {message -> println "Double of $i = $message" } } }}actor.join()doubler.stop()doubler.join() DemoReactor2.groovy
  22. 22. Actorsfinal def doubler = Actors.reactor { 2 * it}Actor actor = Actors.actor { (1..10).each {doubler << it} int i = 0 loop { i += 1 if (i > 10) stop() else { react {message -> println "Double of $i = $message" } } }}actor.join()doubler.stop()doubler.join() DemoReactor2.groovy
  23. 23. Agentsdef jugMembers = new Agent<List<String>>([Me]) //add MejugMembers.send {it.add James} //add James//add Joe using the left-shift operatorfinal Thread t1 = Thread.start { jugMembers << { it.add Joe } }final Thread t2 = Thread.start { jugMembers {it.add Dave} //use the implicit call() method jugMembers {it.add Alice} //use the implicit call() method}[t1, t2]*.join()println jugMembers.valjugMembers.valAsync {println "Current members: $it"}jugMembers.await() DemoAgent.groovy
  24. 24. Resources● ReGinA Chapter 17 - http://manning.com/koenig2/● GPars User Guide - http://gpars.org/0.11/guide/index.html● GPars User Mailing List - http://xircles.codehaus.org/lists/user@gpars.codehaus.org● Dierk Königs presentation (Concurrent programming for you and me) - http://skillsmatter.com/podcast/groovy-grails/concurrent-programming-for-you-and-me● Alex Millers DevWorks article - http://www.ibm.com/developerworks/java/library/j-gpars/index.html● Václav Pechs blog - http://www.jroller.com/vaclav/
  25. 25. Credits● GPars logo contest entries: various, late 2009. Author: various - http://gpars.codehaus.org/Logo+Contest● Giant Fork: A metal four-pronged fork, Jun 2010. Author: dismal_denizen - http://www.openclipart.org/detail/65749● Tree image: Linde von Linn, Jun 2006. Author: Stefan Wernli - http://commons.wikimedia.org/wiki/File:Linde_von_linn.jpg● George Clooney image: Nov 2006. Author: James White/Corbis Outline - http://bit.ly/iCSVal● Meryl Streep image: 2009. Author: unknown - http://gosublogger.com/wp-content/uploads/2009/02/meryl-streep.jpg
  26. 26. Q&A http://bit.ly/gparsbostonmpassell@grovehillsoftware.comhttp://blog.grovehillsoftware.com @softwaregrove

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