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concurrency gpars

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  • 1. ©ASERT2006-2013 Concurrency with GPars Dr Paul King @paulk_asert http:/slideshare.net/paulk_asert/concurrency-gpars https://github.com/paulk-asert/concurrency-gpars
  • 2. Topics Intro • Useful Groovy features for Concurrency • GPars • Case Studies • More Info • Bonus Material GPars - 2 ©ASERT2006-2013
  • 3. "Andy giveth and Bill taketh away" GPars - 3 Source:HerbSutter:http://www.gotw.ca/publications/concurrency-ddj.htm
  • 4. Why is it hard? • Many issues to deal with: – Doing things in parallel, concurrently, asynchronously • Processes, Threads, Co-routines, Events, Scheduling – Sharing/Synchronization Mechanisms • shared memory, locks, transactions, wait/notify, STM, message passing, actors, serializability, persistence, immutability – Abstractions • Shared memory on top of messaging passing • Message passing on top of shared memory • Dataflow, Selective Communication, Continuations – Data Structures and Algorithms • Queues, Heaps, Trees • Sorting, Graph Algorithms GPars - 4
  • 5. Java Concurrency Best Practice? • Java Concurrency in Practice: –“If multiple threads access the same mutable state variable without appropriate synchronization, your program is broken” –“When designing thread-safe classes, good object-oriented techniques – encapsulation, immutability, and clear specification of invariants – are your best friends” GPars - 5
  • 6. Ralph Johnson: Parallel Programming • Styles of parallel programming – Threads and locks – Asynchronous messages e.g. Actors – no or limited shared memory – Sharing with deterministic restrictions e.g. Fork-join – Data parallelism GPars - 6 ©ASERT2006-2013 http://strangeloop2010.com/talk/presentation_file/14485/Johnson-DataParallelism.pdf IncreasingAbstraction
  • 7. Ralph Johnson: Parallel Programming • Styles of parallel programming – Threads and locks • Nondeterministic, low-level, rumored humans can do this – Asynchronous messages e.g. Actors – no or limited shared memory • Nondeterministic, ok for I/O but be careful with side-effects – Sharing with deterministic restrictions e.g. Fork-join • Hopefully deterministic semantics, not designed for I/O – Data parallelism • Deterministic semantics, easy, efficient, not designed for I/O GPars - 7 ©ASERT2006-2013 http://strangeloop2010.com/talk/presentation_file/14485/Johnson-DataParallelism.pdf Each approach has some caveats
  • 8. GPars • http://gpars.codehaus.org/ • Library classes and DSL sugar providing intuitive ways for Groovy developers to handle tasks concurrently. Logical parts: – Data Parallelism features use JSR-166y Parallel Arrays to enable multi-threaded collection processing – Asynchronous functions extend the Java built-in support for executor services to enable multi-threaded closure processing – Dataflow Concurrency supports natural shared-memory concurrency model, using single-assignment variables – Actors provide an implementation of Erlang/Scala-like actors including "remote" actors on other machines & CSP – Safe Agents provide a non-blocking mt-safe reference to mutable state; inspired by "agents" in Clojure GPars - 8 ©ASERT2006-2013
  • 9. Choosing approaches GPars - 9 Formoredetailssee:http://gpars.codehaus.org/Concepts+compared Parallel Collections Data Parallelism Task Parallelism Streamed Data Parallelism Fork/ Join Dataflow operators CSP Actors Dataflow tasks Actors Asynch fun’s CSP Fork/ Join Immutable Stm, Agents Special collections Synchronization Linear Recursive Linear Recursive Shared Data Irregular Regular
  • 10. Coordination approaches GPars - 10 Source:ReGinA–GroovyinAction,2ndedition Data Parallelism: Fork/Join Map/Reduce Fixed coordination (for collections) Actors Explicit coordination Safe Agents Delegated coordination Dataflow Implicit coordination
  • 11. Groovy concurrency value add GPars - 11 JVM Concurrency Threads, synchronization, locks, semaphores, Phaser, executor, fork-join, concurrent collections, atomic objects GPars Map/reduce, fork/join, asynchronous closures, actors, CSP, agents, dataflow concurrency Your Application Groovy Thread & process enhancements, immutability, laziness, @WithReadLock, @WithWriteLock, @Lazy, @Synchronized
  • 12. Immutable Classes • Some Rules – Don’t provide mutators – Ensure that no methods can be overridden • Easiest to make the class final • Or use static factories & non-public constructors – Make all fields final – Make all fields private • Avoid even public immutable constants – Ensure exclusive access to any mutable components • Don’t leak internal references • Defensive copying in and out – Optionally provide equals and hashCode methods – Optionally provide toString method
  • 13. @Immutable... • Java Immutable Class – As per Joshua Bloch Effective Java ©ASERT2006-2013 public final class Person { private final String first; private final String last; public String getFirst() { return first; } public String getLast() { return last; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((first == null) ? 0 : first.hashCode()); result = prime * result + ((last == null) ? 0 : last.hashCode()); return result; } public Person(String first, String last) { this.first = first; this.last = last; } // ... // ... @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (first == null) { if (other.first != null) return false; } else if (!first.equals(other.first)) return false; if (last == null) { if (other.last != null) return false; } else if (!last.equals(other.last)) return false; return true; } @Override public String toString() { return "Person(first:" + first + ", last:" + last + ")"; } }
  • 14. ...@Immutable... • Java Immutable Class – As per Joshua Bloch Effective Java ©ASERT2006-2013 public final class Person { private final String first; private final String last; public String getFirst() { return first; } public String getLast() { return last; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((first == null) ? 0 : first.hashCode()); result = prime * result + ((last == null) ? 0 : last.hashCode()); return result; } public Person(String first, String last) { this.first = first; this.last = last; } // ... // ... @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (first == null) { if (other.first != null) return false; } else if (!first.equals(other.first)) return false; if (last == null) { if (other.last != null) return false; } else if (!last.equals(other.last)) return false; return true; } @Override public String toString() { return "Person(first:" + first + ", last:" + last + ")"; } } boilerplate
  • 15. ...@Immutable ©ASERT2006-2013 @Immutable class Person { String first, last }
  • 16. Approaches to managing collection storage • Mutable • Persistent ©ASERT2006-2013 • Immutable ‘c’ ‘a’ ‘c’ ‘a’ Add ‘t’ Add ‘t’ Add ‘t’ ‘c’ ‘a’ ‘t’ ‘c’ ‘a’ ‘c’ ‘a’ ‘t’ X ‘c’ ‘a’ ‘t’ ‘c’ ‘a’ ArrayList, HashSet, HashMap asImmutable(), Guava, mop tricks fj, clj-ds, pcollections, totallylazy
  • 17. Topics • Intro • Useful Groovy features for Concurrency GPars • Case Studies • More Info • Bonus Material GPars - 17 ©ASERT2006-2013
  • 18. Choosing approaches GPars - 18 Formoredetailssee:http://gpars.codehaus.org/Concepts+compared Parallel Collections Data Parallelism Task Parallelism Streamed Data Parallelism Fork/ Join Dataflow operators CSP Actors Dataflow tasks Actors Asynch fun’s CSP Fork/ Join Immutable Stm, Agents Special collections Synchronization Linear Recursive Linear Recursive Shared Data Irregular Regular
  • 19. Groovy Sequential Collection GPars - 19 ©ASERT2006-2013 def oneStarters = (1..30) .collect { it ** 2 } .findAll { it ==~ '1.*' } assert oneStarters == [1, 16, 100, 121, 144, 169, 196] assert oneStarters.max() == 196 assert oneStarters.sum() == 747
  • 20. GPars Parallel Collections… GPars - 20 ©ASERT2006-2013 import static groovyx.gpars.GParsPool.withPool withPool { def oneStarters = (1..30) .collectParallel { it ** 2 } .findAllParallel { it ==~ '1.*' } assert oneStarters == [1, 16, 100, 121, 144, 169, 196] assert oneStarters.maxParallel() == 196 assert oneStarters.sumParallel() == 747 }
  • 21. …GPars Parallel Collections • Suitable when – Each iteration is independent, i.e. not: fact[index] = index * fact[index - 1] – Iteration logic doesn’t use non-thread safe code – Size and indexing of iteration are important GPars - 21 ©ASERT2006-2013 import static groovyx.gpars.GParsPool.withPool withPool { def oneStarters = (1..30) .collectParallel { it ** 2 } .findAllParallel { it ==~ '1.*' } assert oneStarters == [1, 16, 100, 121, 144, 169, 196] assert oneStarters.maxParallel() == 196 assert oneStarters.sumParallel() == 747 }
  • 22. Parallel Collection Variations • Apply some Groovy metaprogramming GPars - 22 ©ASERT2006-2013 import static groovyx.gpars.GParsPool.withPool withPool { def oneStarters = (1..30).makeConcurrent() .collect { it ** 2 } .findAll { it ==~ '1.*' } .findAll { it ==~ '...' } assert oneStarters == [100, 121, 144, 169, 196] } import groovyx.gpars.ParallelEnhancer def nums = 1..5 ParallelEnhancer.enhanceInstance(nums) assert [1, 4, 9, 16, 25] == nums.collectParallel{ it * it }
  • 23. GPars parallel methods for collections Transparent Transitive? Parallel Lazy? any { ... } anyParallel { ... } yes collect { ... } yes collectParallel { ... } count(filter) countParallel(filter) each { ... } eachParallel { ... } eachWithIndex { ... } eachWithIndexParallel { ... } every { ... } everyParallel { ... } yes find { ... } findParallel { ... } findAll { ... } yes findAllParallel { ... } findAny { ... } findAnyParallel { ... } fold { ... } foldParallel { ... } fold(seed) { ... } foldParallel(seed) { ... } grep(filter) yes grepParallel(filter) groupBy { ... } groupByParallel { ... } max { ... } maxParallel { ... } max() maxParallel() min { ... } minParallel { ... } min() minParallel() split { ... } yes splitParallel { ... } sum sumParallel // foldParallel + GPars - 23Transitive means result is automatically transparent; Lazy means fails fast FormoredetailsseeReGinAortheGParsdocumentation
  • 24. GPars: Map-Reduce GPars - 24 ©ASERT2006-2013 import static groovyx.gpars.GParsPool.withPool withPool { def oneStarters = (1..30).parallel .map { it ** 2 } .filter { it ==~ '1.*' } assert oneStarters.collection == [1, 16, 100, 121, 144, 169, 196] // aggregations/reductions assert oneStarters.max() == 196 assert oneStarters.reduce { a, b -> a + b } == 747 assert oneStarters.sum() == 747 }
  • 25. GPars parallel array methods Method Return Type combine(initValue) { ... } Map filter { ... } Parallel array collection Collection groupBy { ... } Map map { ... } Parallel array max() T max { ... } T min() T min { ... } T reduce { ... } T reduce(seed) { ... } T size() int sort { ... } Parallel array sum() T parallel // on a Collection Parallel array GPars - 25 FormoredetailsseeReGinAortheGParsdocumentation
  • 26. Parallel Collections vs Map-Reduce GPars - 26 Fork Fork JoinJoin Map Map Reduce Map Map Reduce Reduce Map Filter FilterMap
  • 27. Concurrency challenge… • Suppose we have the following calculation involving several functions: • And we want to use our available cores … GPars - 27 ©ASERT2006-2013 // example adapted from Parallel Programming with .Net def (f1, f2, f3, f4) = [{ sleep 1000; it }] * 3 + [{ x, y -> x + y }] def a = 5 def b = f1(a) def c = f2(a) def d = f3(c) def f = f4(b, d) assert f == 10
  • 28. …Concurrency challenge… • We can analyse the example’s task graph: GPars - 28 ©ASERT2006-2013 // example adapted from Parallel Programming with .Net def (f1, f2, f3, f4) = [{ sleep 1000; it }] * 3 + [{ x, y -> x + y }] def a = 5 def b = f1(a) def c = f2(a) def d = f3(c) def f = f4(b, d) assert f == 10 f2 f3 f1 f4 aa b c d f
  • 29. …Concurrency challenge… • Manually using asynchronous functions: GPars - 29 ©ASERT2006-2013 // example adapted from Parallel Programming with .Net def (f1, f2, f3, f4) = [{ sleep 1000; it }] * 3 + [{ x, y -> x + y }] import static groovyx.gpars.GParsPool.withPool withPool(2) { def a = 5 def futureB = f1.callAsync(a) def c = f2(a) def d = f3(c) def f = f4(futureB.get(), d) assert f == 10 } f2 f3 f1 f4 aa b c d f
  • 30. …Concurrency challenge • And with GPars Dataflows: GPars - 30 ©ASERT2006-2013 def (f1, f2, f3, f4) = [{ sleep 1000; it }] * 3 + [{ x, y -> x + y }] import groovyx.gpars.dataflow.Dataflows import static groovyx.gpars.dataflow.Dataflow.task new Dataflows().with { task { a = 5 } task { b = f1(a) } task { c = f2(a) } task { d = f3(c) } task { f = f4(b, d) } assert f == 10 } f2 f3 f1 f4 aa b c d f
  • 31. …Concurrency challenge • And with GPars Dataflows: GPars - 31 ©ASERT2006-2013 def (f1, f2, f3, f4) = [{ sleep 1000; it }] * 3 + [{ x, y -> x + y }] import groovyx.gpars.dataflow.Dataflows import static groovyx.gpars.dataflow.Dataflow.task new Dataflows().with { task { f = f4(b, d) } task { d = f3(c) } task { c = f2(a) } task { b = f1(a) } task { a = 5 } assert f == 10 } f2 f3 f1 f4 aa b c d f
  • 32. GPars: Dataflows... GPars - 32 ©ASERT2006-2013 import groovyx.gpars.dataflow.DataFlows import static groovyx.gpars.dataflow.DataFlow.task final flow = new DataFlows() task { flow.result = flow.x + flow.y } task { flow.x = 10 } task { flow.y = 5 } assert 15 == flow.result new DataFlows().with { task { result = x * y } task { x = 10 } task { y = 5 } assert 50 == result } 510 yx *
  • 33. ...GPars: Dataflows... • Evaluating: GPars - 33 ©ASERT2006-2013 import groovyx.gpars.dataflow.DataFlows import static groovyx.gpars.dataflow.DataFlow.task final flow = new DataFlows() task { flow.a = 10 } task { flow.b = 5 } task { flow.x = flow.a - flow.b } task { flow.y = flow.a + flow.b } task { flow.result = flow.x * flow.y } assert flow.result == 75 b 10 5 a +- * result = (a – b) * (a + b) x y Question: what happens if I change the order of the task statements here?
  • 34. ...GPars: Dataflows... • Naive attempt for loops GPars - 34 ©ASERT2006-2013 import groovyx.gpars.dataflow.Dataflows import static groovyx.gpars.dataflow.Dataflow.task final flow = new Dataflows() [10, 20].each { thisA -> [4, 5].each { thisB -> task { flow.a = thisA } task { flow.b = thisB } task { flow.x = flow.a - flow.b } task { flow.y = flow.a + flow.b } task { flow.result = flow.x * flow.y } println flow.result } } // => java.lang.IllegalStateException: A DataflowVariable can only be assigned once. ... task { flow.a = 10 } ... task { flow.a = 20 } Don’t do this! X
  • 35. ...GPars: Dataflows... GPars - 35 ©ASERT2006-2013 import groovyx.gpars.dataflow.DataflowStream import static groovyx.gpars.dataflow.Dataflow.* final streamA = new DataflowStream() final streamB = new DataflowStream() final streamX = new DataflowStream() final streamY = new DataflowStream() final results = new DataflowStream() operator(inputs: [streamA, streamB], outputs: [streamX, streamY]) { a, b -> streamX << a - b; streamY << a + b } operator(inputs: [streamX, streamY], outputs: [results]) { x, y -> results << x * y } [[10, 20], [4, 5]].combinations().each{ thisA, thisB -> task { streamA << thisA } task { streamB << thisB } } 4.times { println results.val } b 10 10 20 20 4 5 4 5 a +- * 84 75 384 375
  • 36. ...GPars: Dataflows • Suitable when: – Your algorithms can be expressed as mutually- independent logical tasks • Properties: – Inherently safe and robust (no race conditions or livelocks) – Amenable to static analysis – Deadlocks “typically” become repeatable – “Beautiful” (declarative) code GPars - 36 ©ASERT2006-2013 import groovyx.gpars.dataflow.Dataflows import static groovyx.gpars.dataflow.Dataflow.task final flow = new Dataflows() task { flow.x = flow.y } task { flow.y = flow.x }
  • 37. GPars: Dataflow Sieve GPars - 37 ©ASERT2006-2013 final int requestedPrimeNumberCount = 1000 final DataflowStream initialChannel = new DataflowStream() task { (2..10000).each { initialChannel << it } } def filter(inChannel, int prime) { def outChannel = new DataflowStream() operator([inputs: [inChannel], outputs: [outChannel]]) { if (it % prime != 0) { bindOutput it } } return outChannel } def currentOutput = initialChannel requestedPrimeNumberCount.times { int prime = currentOutput.val println "Found: $prime" currentOutput = filter(currentOutput, prime) } Source: http://groovyconsole.appspot.com/script/235002
  • 38. GPars: Actors... • Actors provide explicit coordination: they don’t share state, instead coordinating via asynchronous messages – Contrasting with predefined coordination for fork/join & map/filter/reduce & implicit coordination for dataflow – Messages are processed one at a time normally in the order they were sent (which is non-deterministic due to asynchronous nature) – Some actor systems allowing message delivery to be prioritised; others allow for sharing some (readonly) state; some allow remote actors for load balancing/robustness • Not new in concept – But has received recent publicity due to special support in Erlang, Scala and other languages GPars - 38 ©ASERT2006-2013
  • 39. …GPars: Actors... • Class with the following lifecycle & methods – But also DSL sugar & enhancements GPars - 39 ©ASERT2006-2013 start() stop() act() send(msg) sendAndWait(msg) loop { } react { msg -> } msg.reply(replyMsg) receive() join()
  • 40. …GPars: Actors... GPars - 40 ©ASERT2006-2013 import groovyx.gpars.actor.DynamicDispatchActor class VotingActor extends DynamicDispatchActor { void onMessage(String language) { processVote(language) } void onMessage(List languages) { languages.each{ processVote it } } private processVote(language) { if (language.startsWith('G')) println "You voted for $language" else println 'Sorry, please try again' } } final votes = new VotingActor().start() votes << 'Groovy' votes << 'C++' votes << ['Groovy', 'Go', 'Dart'] votes.stop() votes.join() You voted for Groovy Sorry, please try again You voted for Groovy You voted for Go Sorry, please try again
  • 41. …GPars: Actors... GPars - 41 ©ASERT2006-2013 import static groovyx.gpars.actor.Actors.* def votes = reactor { it.endsWith('y') ? "You voted for $it" : "Sorry, please try again" } println votes.sendAndWait('Groovy') println votes.sendAndWait('JRuby') println votes.sendAndWait('Go') def languages = ['Groovy', 'Dart', 'C++'] def booth = actor { languages.each{ votes << it } loop { languages.size().times { react { println it } } stop() } } booth.join(); votes.stop(); votes.join() You voted for Groovy You voted for JRuby Sorry, please try again You voted for Groovy Sorry, please try again Sorry, please try again
  • 42. …GPars: Actors GPars - 42 ©ASERT2006-2013 import groovyx.gpars.activeobject.* @ActiveObject class VotingActiveObject { @ActiveMethod vote(String language) { processVote(language) } @ActiveMethod vote(List<String> languages) { languages.collect{ processVote it } } private processVote(language) { if (language.size() == 6) "You voted for $language" else 'Sorry, please try again' } } def voter = new VotingActiveObject() def result1 = voter.vote('Scala') def result2 = voter.vote('Groovy') def result3 = voter.vote(['Pascal', 'Clojure', 'Groovy']) [result1.get(), result2.get(), *result3.get()].each{ println it } Sorry, please try again You voted for Groovy You voted for Pascal Sorry, please try again You voted for Groovy
  • 43. Agents... • Agents safeguard non-thread safe objects • Only the agent can update the underlying object • “Code” to update the protected object is sent to the agent • Can be used with other approaches GPars - 43 ©ASERT2006-2013
  • 44. …Agents… GPars - 44 ©ASERT2006-2013 def random = new Random() def randomDelay = { sleep random.nextInt(10) } String result = '' ('a'..'z').each { letter -> Thread.start{ randomDelay() result += letter } } sleep 100 // poor man's join println result println result.size() Unsafe!
  • 45. …Agents… GPars - 45 ©ASERT2006-2013 import groovyx.gpars.agent.Agent def random = new Random() def randomDelay = { sleep random.nextInt(10) } def agent = new Agent<String>('') ('a'..'z').each { letter -> Thread.start{ randomDelay() agent.send{ updateValue it + letter } } } sleep 100 // poor man's join String result = agent.val println result println result.size()
  • 46. …Agents GPars - 46 ©ASERT2006-2013 import groovyx.gpars.agent.Agent def random = new Random() def randomDelay = { sleep random.nextInt(10) } def agent = new Agent<String>('') def threads = ('a'..'z').collect { letter -> Thread.start { randomDelay() agent.send{ updateValue it << letter } } } threads*.join() String result = agent.val println result println result.size()
  • 47. Software Transactional Memory… GPars - 47 ©ASERT2006-2013 @Grab('org.multiverse:multiverse-beta:0.7-RC-1') import org.multiverse.api.references.LongRef import static groovyx.gpars.stm.GParsStm.atomic import static org.multiverse.api.StmUtils.newLongRef class Account { private final LongRef balance Account(long initial) { balance = newLongRef(initial) } void setBalance(long newBalance) { if (newBalance < 0) throw new RuntimeException("not enough money") balance.set newBalance } long getBalance() { balance.get() } } // ...
  • 48. …Software Transactional Memory GPars - 48 ©ASERT2006-2013 // ... def from = new Account(20) def to = new Account(20) def amount = 10 def watcher = Thread.start { 15.times { atomic { println "from: ${from.balance}, to: ${to.balance}" } sleep 100 } } sleep 150 try { atomic { from.balance -= amount to.balance += amount sleep 500 } println 'transfer success' } catch(all) { println all.message } atomic { println "from: $from.balance, to: $to.balance" } watcher.join()
  • 49. Topics • Intro • Useful Groovy features for Concurrency • GPars Case Studies Web Testing Word Split • More Info • Bonus Material GPars - 49 ©ASERT2006-2013
  • 50. GPars for testing GPars - 50 ©ASERT2006-2013 @Grab('net.sourceforge.htmlunit:htmlunit:2.6') import com.gargoylesoftware.htmlunit.WebClient @Grab('org.codehaus.gpars:gpars:0.10') import static groovyx.gpars.GParsPool.* def testCases = [ ['Home', 'Bart', 'Content 1'], ['Work', 'Homer', 'Content 2'], ['Travel', 'Marge', 'Content 3'], ['Food', 'Lisa', 'Content 4'] ] withPool(3) { testCases.eachParallel{ category, author, content -> postAndCheck category, author, content } } private postAndCheck(category, author, content) { ...
  • 51. Topics • Intro • Useful Groovy features for Concurrency • GPars Case Studies Web Testing Word Split • More Info • Bonus Material GPars - 51 ©ASERT2006-2013
  • 52. Word Split with Fortress GPars - 52 ©ASERT2006-2013 Guy Steele’s StrangeLoop keynote (from slide 52 onwards for several slides): http://strangeloop2010.com/talk/presentation_file/14299/GuySteele-parallel.pdf
  • 53. Word Split… GPars - 53 ©ASERT2006-2013 def swords = { s -> def result = [] def word = '' s.each{ ch -> if (ch == ' ') { if (word) result += word word = '' } else word += ch } if (word) result += word result } assert swords("This is a sample") == ['This', 'is', 'a', 'sample'] assert swords("Here is a sesquipedalian string of words") == ['Here', 'is', 'a', 'sesquipedalian', 'string', 'of', 'words']
  • 54. Word Split… GPars - 54 ©ASERT2006-2013 def swords = { s -> def result = [] def word = '' s.each{ ch -> if (ch == ' ') { if (word) result += word word = '' } else word += ch } if (word) result += word result }
  • 55. Word Split… GPars - 55 ©ASERT2006-2013 def swords = { s -> def result = [] def word = '' s.each{ ch -> if (ch == ' ') { if (word) result += word word = '' } else word += ch } if (word) result += word result }
  • 56. …Word Split… GPars - 56 ©ASERT2006-2013
  • 57. …Word Split… GPars - 57 ©ASERT2006-2013
  • 58. Segment(left1, m1, right1) Segment(left2, m2, right2) Segment(left1, m1 + [ ? ] + m2, right2) …Word Split… GPars - 58 ©ASERT2006-2013
  • 59. …Word Split… GPars - 59 ©ASERT2006-2013 class Util { static maybeWord(s) { s ? [s] : [] } } import static Util.* @Immutable class Chunk { String s public static final ZERO = new Chunk('') def plus(Chunk other) { new Chunk(s + other.s) } def plus(Segment other) { new Segment(s + other.l, other.m, other.r) } def flatten() { maybeWord(s) } } @Immutable class Segment { String l; List m; String r public static final ZERO = new Segment('', [], '') def plus(Chunk other) { new Segment(l, m, r + other.s) } def plus(Segment other) { new Segment(l, m + maybeWord(r + other.l) + other.m, other.r) } def flatten() { maybeWord(l) + m + maybeWord(r) } }
  • 60. …Word Split… GPars - 60 ©ASERT2006-2013 def processChar(ch) { ch == ' ' ? new Segment('', [], '') : new Chunk(ch) } def swords(s) { s.inject(Chunk.ZERO) { result, ch -> result + processChar(ch) } } assert swords("Here is a sesquipedalian string of words").flatten() == ['Here', 'is', 'a', 'sesquipedalian', 'string', 'of', 'words']
  • 61. …Word Split… GPars - 61 ©ASERT2006-2013
  • 62. …Word Split… GPars - 62 ©ASERT2006-2013
  • 63. …Word Split… GPars - 63 ©ASERT2006-2013 THREADS = 4 def pwords(s) { int n = (s.size() + THREADS - 1) / THREADS def map = new ConcurrentHashMap() (0..<THREADS).collect { i -> Thread.start { def (min, max) = [ [s.size(), i * n].min(), [s.size(), (i + 1) * n].min() ] map[i] = swords(s[min..<max]) } }*.join() (0..<THREADS).collect { i -> map[i] }.sum().flatten() }
  • 64. …Word Split… GPars - 64 ©ASERT2006-2013 import static groovyx.gpars.GParsPool.withPool THRESHHOLD = 10 def partition(piece) { piece.size() <= THRESHHOLD ? piece : [piece[0..<THRESHHOLD]] + partition(piece.substring(THRESHHOLD)) } def pwords = { input -> withPool(THREADS) { partition(input).parallel.map(swords).reduce{ a, b -> a + b }.flatten() } }
  • 65. …Guy Steele example in Groovy… GPars - 65 ©ASERT2006-2013 def words = { s -> int n = (s.size() + THREADS - 1) / THREADS def min = (0..<THREADS).collectEntries{ [it, [s.size(),it*n].min()] } def max = (0..<THREADS).collectEntries{ [it, [s.size(),(it+1)*n].min()] } def result = new DataFlows().with { task { a = swords(s[min[0]..<max[0]]) } task { b = swords(s[min[1]..<max[1]]) } task { c = swords(s[min[2]..<max[2]]) } task { d = swords(s[min[3]..<max[3]]) } task { sum1 = a + b } task { sum2 = c + d } task { sum = sum1 + sum2 } println 'Tasks ahoy!' sum } switch(result) { case Chunk: return maybeWord(result.s) case Segment: return result.with{ maybeWord(l) + m + maybeWord(r) } } } DataFlow version: partially hard-coded to 4 partitions for easier reading
  • 66. …Guy Steele example in Groovy… GPars - 66 ©ASERT2006-2013 GRANULARITY_THRESHHOLD = 10 THREADS = 4 println GParsPool.withPool(THREADS) { def result = runForkJoin(0, input.size(), input){ first, last, s -> def size = last - first if (size <= GRANULARITY_THRESHHOLD) { swords(s[first..<last]) } else { // divide and conquer def mid = first + ((last - first) >> 1) forkOffChild(first, mid, s) forkOffChild(mid, last, s) childrenResults.sum() } } switch(result) { case Chunk: return maybeWord(result.s) case Segment: return result.with{ maybeWord(l) + m + maybeWord(r) } } } Fork/Join version
  • 67. …Guy Steele example in Groovy GPars - 67 ©ASERT2006-2013 println GParsPool.withPool(THREADS) { def ans = input.collectParallel{ processChar(it) }.sum() switch(ans) { case Chunk: return maybeWord(ans.s) case Segment: return ans.with{ maybeWord(l) + m + maybeWord(r) } } } Just leveraging the algorithm’s parallel nature
  • 68. Topics • Intro • Useful Groovy features for Concurrency • Gpars • Case Studies More Info • Bonus Material GPars - 68 ©ASERT2006-2013
  • 69. More Information about Concurrency • Web sites – http://gpars.codehaus.org/ – http://g.oswego.edu/ Doug Lea's home page – http://gee.cs.oswego.edu/dl/concurrency-interest/ – http://jcip.net/ Companion site for Java Concurrency in Practice – http://www.eecs.usma.edu/webs/people/okasaki/pubs.html#cup98 Purely Functional Data Structures – http://delicious.com/kragen/concurrency Concurrency bookmark list – http://www.gotw.ca/publications/concurrency-ddj.htm The Free Lunch is Over, Herb Sutter – http://manticore.cs.uchicago.edu/papers/damp07.pdf – http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10142 Concepts, Techniques, and Models of Computer Programming GPars - 69
  • 70. More Information about Groovy • Web sites – http://groovy.codehaus.org – http://grails.codehaus.org – http://pleac.sourceforge.net/pleac_groovy (many examples) – http://www.asert.com.au/training/java/GV110.htm (workshop) • Mailing list for users – user@groovy.codehaus.org • Information portals – http://www.aboutgroovy.org – http://www.groovyblogs.org • Documentation (1000+ pages) – Getting Started Guide, User Guide, Developer Guide, Testing Guide, Cookbook Examples, Advanced Usage Guide • Books – Several to choose from ... GPars - 70
  • 71. More Information: Groovy in Action GPars - 71 Contains a chapter on GPars!
  • 72. Bonus Material • Other concurrency options • Dining Philosopher Case Study GPars - 72 ©ASERT2006-2013
  • 73. Bonus Material • Other concurrency options – Jetlang – JPPF – Multiverse – Gruple – Cascading – GridGain – ConTest GPars - 73 ©ASERT2006-2013
  • 74. Lightweight threads: Jetlang • Jetlang – A high performance threading library – http://code.google.com/p/jetlang/ GPars - 74 import org.jetlang.fibers.ThreadFiber import org.jetlang.channels.MemoryRequestChannel import org.jetlang.channels.AsyncRequest def req = new ThreadFiber() // or pool def reply = new ThreadFiber() def channel = new MemoryRequestChannel() req.start() reply.start() channel.subscribe(reply) { it.reply(it.request.sum()) } AsyncRequest.withOneReply(req, channel, [3, 4, 5]) { println it } sleep 1000 req.dispose() reply.dispose() 12
  • 75. Other High-Level Libraries: JPPF – Open source Grid Computing platform – http://www.jppf.org/ GPars - 75 import org.jppf.client.* import java.util.concurrent.Callable class Task implements Callable, Serializable { private static final long serialVersionUID = 1162L public Object call() { println 'Executing Groovy' "Hello JPPF from Groovy" } } def client = new JPPFClient() def job = new JPPFJob() def task = new Task() job.addTask task def results = client.submit(job) for (t in results) { if (t.exception) throw t.exception println "Result: " + t.result }
  • 76. Other High-Level Libraries: Gruple... – http://code.google.com/p/gruple – Simple abstraction to coordinate and synchronize threads with ease – based on Tuplespaces • Tuplespaces provide the illusion of a shared memory on top of a message passing system, along with a small set of operations to greatly simplify parallel programming – Example Tuple: [fname:"Vanessa", lname:"Williams", project:"Gruple"] – Basic operations within a Tuplespace are: • put - insert a tuple into the space • get - read a tuple from the space (non-destructively) • take - take a tuple from the space (a destructive read) – Further reading: Eric Freeman, Susanne Hupfer, and Ken Arnold. JavaSpaces Principles, Patterns, and Practice, Addison Wesley, 1999 GPars - 76
  • 77. …Other High-Level Libraries: Gruple... GPars - 77 import org.gruple.SpaceService def defaultSpace = SpaceService.getSpace() defaultSpace << [fname:"Vanessa", lname:"Williams", project:"Gruple"] println defaultSpace.get(fname:"Vanessa", lname:"Williams", project:"Gruple") [project:Gruple, lname:Williams, fname:Vanessa]
  • 78. Other High-Level Libraries: ...Gruple... – Mandelbrot example (included in Gruple download) GPars - 78 ... Space space = SpaceService.getSpace("mandelbrot") Map template = createTaskTemplate() Map task String threadName = Thread.currentThread().name while(true) { ArrayList points task = space.take(template) println "Worker $threadName got task ${task['start']} for job ${task['jobId'] points = calculateMandelbrot(task) Map result = createResult(task['jobId'], task['start'], points) println "Worker $threadName writing result for task ${result['start']} for jo space.put(result) } ...
  • 79. Other High-Level Libraries: ...Gruple GPars - 79
  • 80. Other High-Level Libraries: Cascading.groovy – API/DSL for executing tasks on a Hadoop cluster – http://www.cascading.org/ GPars - 80 def assembly = builder.assembly(name: "wordcount") { eachTuple(args: ["line"], results: ["word"]) { regexSplitGenerator(declared: ["word"], pattern: /[.,]*s+/) } group(["word"]) everyGroup(args: ["word"], results: ["word", "count"]) { count() } group(["count"], reverse: true) } def map = builder.map() { source(name: "wordcount") { hfs(input) { text(["line"]) } } sink(name: "wordcount") { hfs(output) { text() } } } def flow = builder.flow(name: "wordcount", map: map, assembly: assembly)
  • 81. Other High-Level Libraries: GridGain… – Simple & productive to use grid computing platform – http://www.gridgain.com/ GPars - 81 class GridHelloWorldGroovyTask extends GridTaskSplitAdapter<String, Integer> { Collection split(int gridSize, Object phrase) throws GridException { // ... } Object reduce(List results) throws GridException { // ... } } import static GridFactory.* start() def grid = getGrid() def future = grid.execute(GridHelloWorldGroovyTask, "Hello World") def phraseLen = future.get() stop(true)
  • 82. …Other High-Level Libraries: GridGain • http://gridgain.blogspot.com/2010/10/worlds-shortest-mapreduce- app.html GPars - 82 words = "Counting Letters In This Phrase".split(' ') map = new C1() { def apply(word) { word.size() } } reduce = sumIntReducer() println grid.forkjoin(SPREAD, yield(words, map), reduce) // => 27 grid.forkjoin(SPREAD,yield("Counting Letters In This Phrase".split(' '), new C1(){def apply(w){w.size()}}),sumReducer())
  • 83. Testing multi-threaded applications: ConTest... • Advanced Testing for Multi-Threaded Applications – Tool for testing, debugging, and coverage-measuring of concurrent programs (collects runtime statistics) – Systematically and transparently (using a java agent) schedules the execution of program threads in ways likely to reveal race conditions, deadlocks, and other intermittent bugs (collectively called synchronization problems) with higher than normal frequency – The ConTest run-time engine adds heuristically controlled conditional instructions (adjustable by a preferences file) that force thread switches, thus helping to reveal concurrent bugs. You can use existing tests and run ConTest multiple times – by default different heuristics used each time it is run • http://www.alphaworks.ibm.com/tech/contest GPars - 83
  • 84. ...Testing multi-threaded applications: ConTest GPars - 84 NUM = 5 count = 0 def incThread = { n -> Thread.start{ sleep n*10 //synchronized(ParalInc) { count++ //} } } def threads = (1..NUM).collect(incThread) threads.each{ it.join() } assert count == NUM targetClasses = ParalInc timeoutTampering = true noiseFrequency = 500 strength = 10000 Exception in thread "main" Assertion failed: assert count == NUM | | | 4 | 5 false > groovyc ParalInc.groovy > java -javaagent:../../Lib/ConTest.jar -cp %GROOVY_JAR%;. ParalInc ParalInc.groovy
  • 85. Bonus Material • Dining Philosopher’s Case Study – GPars Actors – GPars CSP – Multiverse – Jetlang – Gruple GPars - 85 ©ASERT2006-2013
  • 86. Dining Philosophers… GPars - 86 Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Fork Available | InUse Fork Available | InUse Fork Available | InUse Fork Available | InUse Fork Available | InUse
  • 87. …Dining Philosophers GPars - 87 Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Philosopher Thinking | Eating Fork Available | InUse Fork Available | InUse Fork Available | InUse Fork Available | InUse Fork Available | InUse Accepted | Rejected Take | Release Take | Release
  • 88. Dining Philosophers: Actors... GPars - 88 ©ASERT2006-2013 // adapted from GPars example, repo: http://git.codehaus.org/gitweb.cgi?p=gpars.git // file: src/test/groovy/groovyx/gpars/samples/actors/DemoDiningPhilosophers.groovy @Grab('org.codehaus.gpars:gpars:0.10') import groovyx.gpars.actor.* import groovy.beans.Bindable def names = ['socrates', 'plato', 'aristotle', 'descartes', 'nietzsche'] Actors.defaultActorPGroup.resize names.size() class Philosopher extends AbstractPooledActor { private random = new Random() String name int timesEaten = 0 def forks @Bindable String status void act() { assert 2 == forks.size() loop { think() forks*.send new Take() react {a -> react {b -> if ([a, b].any {Rejected.isCase it}) { [a, b].find {Accepted.isCase it}?.reply new Release() } else { eat() [a, b]*.reply new Release() } } } } }
  • 89. …Dining Philosophers: Actors... GPars - 89 ©ASERT2006-2013 … void think() { setStatus('thinking') sleep random.nextInt(5000) setStatus('') } void eat() { setStatus("eating ${++timesEaten}") sleep random.nextInt(3000) setStatus('') } String toString() { switch (timesEaten) { case 0: return "$name has starved" case 1: return "$name has eaten once" default: return "$name has eaten $timesEaten times" } } } final class Take {} final class Accepted {} final class Rejected {} final class Release {}
  • 90. …Dining Philosophers: Actors... GPars - 90 ©ASERT2006-2013 … class Fork extends AbstractPooledActor { String name boolean available = true void act() { loop { react {message -> switch (message) { case Take: if (available) { available = false reply new Accepted() } else reply new Rejected() break case Release: assert !available available = true break default: throw new IllegalStateException("Cannot process the message: $message") } } } } } def forks = (1..names.size()).collect { new Fork(name: "Fork $it") } def philosophers = (1..names.size()).collect { new Philosopher(name: names[it - 1], forks: [forks[it - 1], forks[it % names.size()]]) }
  • 91. …Dining Philosophers: Actors GPars - 91 ©ASERT2006-2013 … import groovy.swing.* import java.awt.Font import static javax.swing.JFrame.* def frame = new SwingBuilder().frame(title: 'Philosophers', defaultCloseOperation: EXIT_ON_CLOSE) { vbox { hbox { (0..<names.size()).each { i -> def widget = textField(id: names[i], text: names[i].center(14)) widget.font = new Font(widget.font.name, widget.font.style, 36) philosophers[i].propertyChange = { widget.text = philosophers[i].status.center(14) } } } } } frame.pack() frame.visible = true forks*.start() sleep 1000 philosophers*.start() sleep 10000 forks*.stop() forks*.join() philosophers*.stop() philosophers*.join() frame.dispose() philosophers.each { println it } socrates has eaten 3 times plato has eaten 3 times aristotle has eaten 6 times descartes has eaten 2 times nietzsche has eaten 5 times
  • 92. Dining Philosophers: CSP... GPars - 92 ©ASERT2006-2013 // inspired by similar examples at the web sites below: // http://www.cs.kent.ac.uk/projects/ofa/jcsp/ // http://www.soc.napier.ac.uk/~jmk/#_Toc271192596 @Grab('org.codehaus.gpars:gpars:0.10') import org.jcsp.lang.* import groovyx.gpars.csp.PAR import groovyx.gpars.csp.ALT import static java.lang.System.currentTimeMillis def names = ['socrates', 'plato', 'aristotle', 'descartes', 'nietzsche'] enum ForkAction { Take, Release, Stop } import static ForkAction.* class Philosopher implements CSProcess { ChannelOutput leftFork, rightFork String name def forks = [] private random = new Random() private timesEaten = 0 private start = currentTimeMillis() void run() { while (currentTimeMillis() - start < 10000) { think() eat() } [leftFork, rightFork].each { it.write(Stop) } println toString() } …
  • 93. …Dining Philosophers: CSP... GPars - 93 ©ASERT2006-2013 … void think() { println "$name is thinking" sleep random.nextInt(50) } void eat() { [leftFork, rightFork].each { it.write(Take) } println "$name is EATING" timesEaten++ sleep random.nextInt(200) [leftFork, rightFork].each { it.write(Release) } } String toString() { switch (timesEaten) { case 0: return "$name has starved" case 1: return "$name has eaten once" default: return "$name has eaten $timesEaten times" } } }
  • 94. …Dining Philosophers: CSP... GPars - 94 ©ASERT2006-2013 … class Fork implements CSProcess { ChannelInput left, right private active = [0, 1] as Set void run() { def fromPhilosopher = [left, right] def forkAlt = new ALT(fromPhilosopher) while (active) { def i = forkAlt.select() read fromPhilosopher, i, Take read fromPhilosopher, i, Release } } void read(phil, index, expected) { if (!active.contains(index)) return def m = phil[index].read() if (m == Stop) active -= index else assert m == expected } } …
  • 95. …Dining Philosophers: CSP GPars - 95 ©ASERT2006-2013 … def lefts = Channel.createOne2One(names.size()) def rights = Channel.createOne2One(names.size()) def philosophers = (0..<names.size()).collect { i -> return new Philosopher(leftFork: lefts[i].out(), rightFork: rights[i].out(), name: names[i]) } def forks = (0..<names.size()).collect { i -> return new Fork(left: lefts[i].in(), right: rights[(i + 1) % names.size()].in()) } def processList = philosophers + forks new PAR(processList).run()
  • 96. Why CSP? • Amenable to proof and analysis GPars - 96 Picture source: http://wotug.org/parallel/theory/formal/csp/Deadlock/
  • 97. Multiverse Philosophers… GPars - 97 //@Grab('org.multiverse:multiverse-core:0.7-SNAPSHOT') //@Grab('org.multiverse:multiverse-alpha:0.7-SNAPSHOT') //@Grab('org.multiverse:multiverse-groovy:0.7-SNAPSHOT') //@GrabConfig(systemClassLoader=true, initContextClassLoader = true) // adapted multiverse Groovy example: http://git.codehaus.org/gitweb.cgi?p=multiverse.git // file: multiverse-groovy/src/test/groovy/org/multiverse/integration/ org/multiverse/integration/examples/DiningPhilosphersTest.groovy import org.multiverse.transactional.refs.BooleanRef import org.multiverse.transactional.refs.IntRef import static MultiverseGroovyLibrary.* def food = new IntRef(5) def names = ['socrates', 'plato', 'aristotle', 'descartes', 'nietzsche'] def forks = (1..5).collect { new Fork(id: it, free: new BooleanRef(true)) } def philosophers = (0..4).collect { new Philosopher(name: names[it], food: food, left: forks[(it + 1) % 5], right: forks[it]) } def threads = philosophers.collect { new Thread(it) } threads*.start() threads*.join() philosophers.each { println it } class Fork { int id BooleanRef free void take() { free.set(false) } void release() { free.set(true) } }
  • 98. …Multiverse Philosophers GPars - 98 class Philosopher implements Runnable { String name Fork left, right IntRef timesEaten = new IntRef() IntRef food void eat() { atomic(trackreads: true, explicitRetryAllowed: true) { left.free.await(true) right.free.await(true) if (food.get() > 0) { left.take(); right.take() timesEaten.inc(); sleep 10; food.dec() } } } void think() { atomic(trackreads: true, explicitRetryAllowed: true) { left.release(); right.release() } sleep 10 } void run() { 10.times { eat(); think() } } String toString() { switch (timesEaten) { case 0: return "$name has starved" case 1: return "$name has eaten once" default: return "$name has eaten $timesEaten times" } } }
  • 99. Jetlang Philosophers… GPars - 99 import org.jetlang.core.Callback import org.jetlang.fibers.ThreadFiber import org.jetlang.channels.* def names = ['socrates', 'plato', 'aristotle', 'descartes', 'nietzsche'] class Philosopher implements Callback { private random = new Random() String name int timesEaten = 0 String status def forks private channels = [new MemoryRequestChannel(), new MemoryRequestChannel()] private req = new ThreadFiber() private reply = new ThreadFiber() private responses = [] private gotFork = { it instanceof Accepted } void start() { assert forks.size() == 2 req.start() reply.start() (0..1).each{ channels[it].subscribe(reply, forks[it]) } think() } String toString() { switch (timesEaten) { case 0: return "$name has starved" case 1: return "$name has eaten once" default: return "$name has eaten $timesEaten times" } }
  • 100. …Jetlang Philosophers… GPars - 100 … void think() { println(name + ' is thinking') sleep random.nextInt(3000) (0..1).each{ AsyncRequest.withOneReply(req, channels[it], new Take(it), this); } } void eat() { timesEaten++ println toString() sleep random.nextInt(2000) } void onMessage(Object message) { responses << message if (responses.size() == 2) { if (responses.every(gotFork)) { eat() } responses.findAll(gotFork).each { int index = it.index channels[index].publish(req, new Release(index), forks[index]) } responses = [] think() } } } @Immutable class Take { int index } @Immutable class Accepted { int index } @Immutable class Rejected { int index } @Immutable class Release { int index } …
  • 101. …Jetlang Philosophers GPars - 101 … class Fork implements Callback { String name def holder = [] void onMessage(message) { def msg = message instanceof Request ? message.request : message def index = msg.index switch (msg) { case Take: if (!holder) { holder << index message.reply(new Accepted(index)) } else message.reply(new Rejected(index)) break case Release: assert holder == [index] holder = [] break default: throw new IllegalStateException("Cannot process the message: $message") } } } def forks = (1..names.size()).collect { new Fork(name: "Fork $it") } def philosophers = (1..names.size()).collect { new Philosopher(name: names[it - 1], forks: [forks[it - 1], forks[it % names.size()]]) } philosophers*.start() sleep 10000 philosophers.each { println it }
  • 102. Gruple Philosophers… GPars - 102 import org.gruple.SpaceService import org.gruple.Space class Philosopher { private random = new Random() String name Space space private timesEaten = 0 int id, num boolean done = false void run() { while (true) { think() if (done) return space.take(fork: id) space.take(fork: (id + 1) % num) eat() space.put(fork: id) space.put(fork: (id + 1) % num) } } void think() { println "$name is thinking" sleep random.nextInt(500) } void eat() { println "$name is EATING" timesEaten++ sleep random.nextInt(1000) } … … socrates is thinking nietzsche is thinking descartes is EATING aristotle is EATING descartes is thinking plato is EATING aristotle is thinking socrates is EATING plato is thinking nietzsche is EATING socrates is thinking nietzsche is thinking descartes is EATING descartes is thinking socrates has eaten 5 times plato has eaten 4 times aristotle has eaten 4 times descartes has eaten 4 times nietzsche has eaten 5 times
  • 103. …Gruple Philosophers GPars - 103 … String toString() { switch (timesEaten) { case 0: return "$name has starved" case 1: return "$name has eaten once" default: return "$name has eaten $timesEaten times" } } } def names = ['socrates', 'plato', 'aristotle', 'descartes', 'nietzsche'] def diningSpace = SpaceService.getSpace('Dining') def philosophers = (0..<names.size()).collect{ new Philosopher(name: names[it], id: it, space: diningSpace, num: names.size()) } (0..<names.size()).each{ diningSpace << [fork: it] } sleep 500 def threads = (0..<names.size()).collect{ n -> Thread.start{ philosophers[n].run() } } sleep 10000 philosophers*.done = true sleep 2000 threads.join() println() philosophers.each{ println it }

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