Gpars concepts explained

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GPars Groovy ParallelSystems Václav Pech

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About me Passionateprogrammer

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Concurrency enthusiast

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GPars @ Codehauslead

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Technology evangelist @JetBrains

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JetBrains Academy memberhttp://www.jroller.com/vaclav http://twitter.com/vaclav_pech

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GPars Apache 2license Hosted @ Codehaus 7 commiters Tight relation with the Groovy team Originally named GParallelizer

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Pantha rei Enteringa new era!

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We’re quad corealready Beware: More cores to come shortly!

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Stone age ofparallel SW Dead-locks

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Live-locks

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Race conditions

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Starvation

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Shared Mutable State

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Locks and threadsMultithreaded programs today work mostly by accident!

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Toolset Fork/Join ActorsCollections Dataflow Safe

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Parallel Collection ProcessingwithPool { images. findAllParallel {it.contains me} . collectParallel {convert it} . groupByParallel {it.size()} } Important: Side-effect-free functions only!

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Transparently parallel withPool( 4 ) { images. makeTransparent() . findAll {it.contains me} . collect {convert it} . groupBy {it.size()} }

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Parallelize existing codebuyBargain stocks. makeTransparent() def buyBargain(stocks) { buy stocks. findAll { it.download().price < 50 } } Use with CAUTION!

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Functional flavor Map/ Reduce map, reduce, filter, min, max, sum, … (1..n).parallel.filter {it%2==0} .map {it ** 2} .reduce {a, b -> a + b}

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Call closures asynchronouslydef isSelfPortrait = {image -> image.contains me} SYNC: def flag = isSelfPortrait. call (img1) ASYNC: def future = isSelfPortrait. callAsync (img1) … def flag = future.get()

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Asynchronous closures def resize = {img -> img.resize(64, 64)} def fastResize = resize. async() def resized = images.collect fastResize … createAlbum resized*.get()

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Fork/Join Solve hierarchicalproblems Divide and conquer Merge sort, Quick sort

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Tree traversal

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File scan /search

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… [a, b,c, d, e, f, g, h] [a, b, c, d] [e, f, g, h] [a, b] [c, d] [e, f] [g, h]

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Fork/Join Orchestration runForkJoin(newFile( “./src” )) {currentDir -> long count = 0; currentDir.eachFile { if (it.isDirectory()) { println "Forking a thread for $it" forkOffChild it } else { count++ } } return count + childrenResults .sum(0) } Waits for children without blocking the thread!

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GroovyDSL – IntelliJIDEA CE

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Dataflow Concurrency Norace-conditions

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No live-locks

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Deterministic deadlocks Completely deterministic programs BEAUTIFUL code (Jonas Bonér)

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Dataflow Variables /Promises main task2 task3 x y z task1

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Dataflow Variables task{ z << x.val + y.val } task { x << 40 } task { y << 2 } assert 42 == z.val Single-assignment variables with blocking read

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DataFlows def df = new DataFlows () task { df .z = df .x + df .y } task { df .x = 10 } task { df .y = 5 } assert 15 == df .z

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DataFlows Making Moneydef stocks = ['AAPL', 'GOOG', 'IBM', 'JAVA'] def price = new DataFlows() stocks.each( {stock -> price [stock] = getClosing(stock, 2008) }.async()) def topStock = stocks.max { price [it] }

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Dataflow Operators operator(inputs:[stocksStream], outputs: [pricedStocks]) { stock -> def price = getClosing( stock , 2008) bindOutput(0, [stock: stock , price: price ]) } * + <>

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Actors Isolated

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Communicating Immutable messagesActive Pooled shared threads Activities Create a new actor

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Send a message

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Receive a messageActor Actor Actor Actor Actor Actor Actor T T T Thread pool

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Actors use GateKeeper Form HTTP Finger Prints Address Check Email Check Process Fraud Detect Response SOAP SMTP

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Actors patterns EnricherRouter Translator Endpoint Splitter Agregator Filter Resequencer Checker

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Creating Actors classMyActor extends AbstractPooledActor { void act() { def buddy = new YourActor() buddy << ‘Hi man, how\’re things?’ def response = receive () } }

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Creating Actors defdecryptor = actor { loop { react {msg -> reply msg.reverse() } } } decryptor << ‘noitcA nI yvoorG’

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Sending messages buddy.send 10.eur buddy << new Book(title: ’Groovy Recipes’ , author: ’Scott Davis’ ) def canChat = buddy. sendAndWait ‘Got time?’ buddy. sendAndContinue ‘Need money!’ , {cash-> pocket.add cash }

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Reacting to messagesreact {gift1 -> reply ”Thank you for $gift1” react {gift2 -> reply ”Wow, one more $gift2” [gift1, gift2].max{it.price}. reply ‘ Will you marry me?’ } //Never reached }

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Choosing the Reactionreact / receive {gift -> switch (gift) { case Money: reply ‘Thanks’ ;pocket gift; break case [iPhone, iPod]:child << gift; break case (BigFlat..SmallHouse):moveIn(gift); break case Clothes: putOn(gift) fits(gift)?reply ‘Thanks’ : reply gift break case EXIT: stop() } }

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Continuation Style loop { … react { … react { /*schedule the block; throw CONTINUE*/ … } //Never reached } //Never reached } //Never reached

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Receiving messages defgift = receive () reply ”Thank you for $gift” gift = receive () reply ”Wow, one more $gift” Blocks the calling thread

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Dynamic Dispatch Actordef actor = new DynamicDispatchActor ({ when {BigDecimal num -> println 'Received BigDecimal' } when {String code -> compileAndRun code } when {Book book -> read book } })

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Agent Lock Shared Mutable State in a Safe Alter the State Alter the State

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Agent inside DoubleIncrement Add 25 Message Queue 36 thread

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Agent List defjugMembers = new Agent( ['Me'] ) //add Me task { jugMembers.send {it.add 'Joe'} //add Joe } task { jugMembers << {it.add 'Dave'} //add Dave jugMembers << {it.add 'Alice'} //add Alice } ... println jugMembers. val

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Agent-based Shopping CartCart cart = new Cart()

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cart.addItem 'Pilsner', 10

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cart.addItem 'Budweisser', 5

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cart.removeItem 'Budweisser‘

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cart.increaseQuantity 'Budweisser', 3

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Cart implementation classShoppingCart { private def cartState = new Agent( [:] ) public void addItem(String product, int quantity) { cartState << {it[product] = quantity} } public void removeItem(String product) { cartState << {it.remove(product)} } public Object listContent() { return cartState. val }

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Integration Bundled withGroovy dists

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Maven

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Gradle

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Grape (@Grab)

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Griffon plugin

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Grails plugin

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Roadmap Actor performanceActor and DataFlow remoting CSP implementation STM?, ActiveObjects?

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No more threadsand locks images.parallel. map { //concurrency agnostic code here } def myActor = actor { //concurrency agnostic code here } Identically with agents, fork/join, dataflow, …

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Summary Tasty concurrencymenu Actors, Collections, Dataflow, Safe, … Enjoyable parallelism http://gpars.codehaus.org

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Questions?

Gpars concepts explained

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