Functional Groovy

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Dr Paul King

@paulk_asert

http:/slideshare.net/paulk_asert/functional-groovy

https://github.com/paulk-asert/functional-groovy

Functional Groov

Topics

Intro

• Functional Style

• Design Patterns

• Immutability

• Laziness

• GPars

• Word Split (bonus material)

• More Info

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Introduction

• What is functional programming? – Favour evaluation of composable

expressions over execution of commands

– Encourage particular idioms such as side-

effect free functions & immutability

• And why should I care?

– Declarative understandable code

– Reduction of errors

– Better patterns and approaches to design

– Improved reusability

– Leverage concurrency

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What makes up functional style?

• Functions, Closures, Lambda, Blocks as

first-class citizens

• Higher order functions

• Mutable vs Immutable data structures

• Recursion

• Lazy vs Eager evaluation

• Declarative vs Imperative style

• Advanced Techniques – Memoization, Trampolines, Composition and Curry

• Compile-time safety

• Concurrency






• Recursion





• Concurrency

Using Closures...

• Code deserves to be free

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public class Main { public static void main(String[] args) { print(reverse("Hello")); } public static String reverse(String arg) { return arg.reverse(); } public void static print(String arg) { System.out.println(arg); } } Main.main();

...Using Closures...

• Code deserves to be free

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def codeListInG = [ { println it }, { it.reverse() } ] def main(first, second, arg) { def third = second >> first third(arg) } // def main = { Closure first, Closure second, String arg -> // def mainClosure = this.&main main(codeListInG[0], codeListInG[1], "Hello") // => olleH

def code = { arg -> println "Hello $arg" } code.call('Washington') code('Washington') // => Hello Washington

...Using Closures...

• Used for many things in Groovy: • Iterators

• Callbacks

• Higher-order functions

• Specialized control structures

• Dynamic method definition

• Resource allocation

• Threads

• Continuation-like coding

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def houston(Closure doit) { (10..1).each { count -> doit(count) } } houston { println it }

new File('/x.txt').eachLine { println it }

3.times { println 'Hi' } [0, 1, 2].each { number -> println number } [0, 1, 2].each { println it} def printit = { println it } [0, 1, 2].each printit

...Using Closures

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import static Math.* piA = { 22 / 7 } piB = { 333/106 } piC = { 355/113 } piD = { 0.6 * (3 + sqrt(5)) } piE = { 22/17 + 37/47 + 88/83 } piF = { sqrt(sqrt(2143/22)) } howCloseToPI = { abs(it.value() - PI) } algorithms = [piA:piA, piB:piB, piC:piC, piD:piD, piE:piE, piF:piF] findBestPI(algorithms) def findBestPI(map) { map.entrySet().sort(howCloseToPI).each { entry -> def diff = howCloseToPI(entry) println "Algorithm $entry.key differs by $diff" } }

Algorithm piE differs by 1.0206946399193839E-11 Algorithm piF differs by 1.0070735356748628E-9 Algorithm piC differs by 2.668102068170697E-7 Algorithm piD differs by 4.813291008076703E-5 Algorithm piB differs by 8.321958979307098E-5 Algorithm piA differs by 0.001264489310206951

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Better Design Patterns: Builder

<html> <head> <title>Hello</title> </head> <body> <ul> <li>world 1</li> <li>world 2</li> <li>world 3</li> <li>world 4</li> <li>world 5</li> </ul> </body> </html>

import groovy.xml.* def page = new MarkupBuilder() page.html { head { title 'Hello' } body { ul { for (count in 1..5) { li "world $count" } } } }

• Markup Builder

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SwingBuilder import java.awt.FlowLayout builder = new groovy.swing.SwingBuilder() langs = ["Groovy", "Ruby", "Python", "Pnuts"] gui = builder.frame(size: [290, 100], title: 'Swinging with Groovy!') { panel(layout: new FlowLayout()) { panel(layout: new FlowLayout()) { for (lang in langs) { checkBox(text: lang) } } button(text: 'Groovy Button', actionPerformed: { builder.optionPane(message: 'Indubitably Groovy!'). createDialog(null, 'Zen Message').show() }) button(text: 'Groovy Quit', actionPerformed: {System.exit(0)}) } } gui.show()

Source: http://www.ibm.com/developerworks/java/library/j-pg04125/

Better File Manipulation...

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import java.util.List; import java.util.ArrayList; import java.util.Arrays; import java.io.File; import java.io.FileOutputStream; import java.io.PrintWriter; import java.io.FileNotFoundException; import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.FileInputStream;

public class PrintJavaSourceFileLinesThatContainTheWordJava { public static void main(String[] args) { File outfile = new File("result.txt"); outfile.delete(); File basedir = new File(".."); List<File> files = new ArrayList<File>(); files.add(basedir); FileOutputStream fos = null; PrintWriter out = null; try { fos = new FileOutputStream(outfile); out = new PrintWriter(fos); while (!files.isEmpty()) { File file = files.remove(0); if (file.isDirectory()) { files.addAll(Arrays.asList(file.listFiles())); } else { if (file.getName().endsWith(".java")) { processFile(file, out); } } } } catch (FileNotFoundException e) { e.printStackTrace(); } finally { if (out != null) { out.close(); } if (fos != null) { try { fos.close(); } catch (IOException e) { e.printStackTrace(); } } } } // ...

// ... private static void processFile(File file, PrintWriter out) { FileInputStream fis = null; InputStreamReader isr = null; BufferedReader reader = null; try { fis = new FileInputStream(file); isr = new InputStreamReader(fis); reader = new BufferedReader(isr); String nextline; int count = 0; while ((nextline = reader.readLine()) != null) { count++; if (nextline.toLowerCase().contains("java")) { out.println("File '" + file + "' on line " + count); out.println(nextline); out.println(); } } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (reader != null) { try { reader.close(); } catch (IOException e) { e.printStackTrace(); } } if (isr != null) { try { isr.close(); } catch (IOException e) { e.printStackTrace(); } } if (fis != null) { try { fis.close(); } catch (IOException e) { e.printStackTrace(); } } } } }

...Better File Manipulation...

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import java.util.List; import java.util.ArrayList; import java.util.Arrays; import java.io.File; import java.io.FileOutputStream; import java.io.PrintWriter; import java.io.FileNotFoundException; import java.io.IOException; import java.io.BufferedReader; import java.io.InputStreamReader; import java.io.FileInputStream;

public class PrintJavaSourceFileLinesThatContainTheWordJava { public static void main(String[] args) { File outfile = new File("result.txt"); outfile.delete(); File basedir = new File(".."); List<File> files = new ArrayList<File>(); files.add(basedir); FileOutputStream fos = null; PrintWriter out = null; try { fos = new FileOutputStream(outfile); out = new PrintWriter(fos); while (!files.isEmpty()) { File file = files.remove(0); if (file.isDirectory()) { files.addAll(Arrays.asList(file.listFiles())); } else { if (file.getName().endsWith(".java")) { processFile(file, out); } } } } catch (FileNotFoundException e) { e.printStackTrace(); } finally { if (out != null) { out.close(); } if (fos != null) { try { fos.close(); } catch (IOException e) { e.printStackTrace(); } } } } // ...

// ... private static void processFile(File file, PrintWriter out) { FileInputStream fis = null; InputStreamReader isr = null; BufferedReader reader = null; try { fis = new FileInputStream(file); isr = new InputStreamReader(fis); reader = new BufferedReader(isr); String nextline; int count = 0; while ((nextline = reader.readLine()) != null) { count++; if (nextline.toLowerCase().contains("java")) { out.println("File '" + file + "' on line " + count); out.println(nextline); out.println(); } } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (reader != null) { try { reader.close(); } catch (IOException e) { e.printStackTrace(); } } if (isr != null) { try { isr.close(); } catch (IOException e) { e.printStackTrace(); } } if (fis != null) { try { fis.close(); } catch (IOException e) { e.printStackTrace(); } } } } }

boilerplate

...Better File Manipulation

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def out = new File('result.txt') out.delete() new File('..').eachFileRecurse { file -> if (file.name.endsWith('.groovy')) { file.eachLine { line, num -> if (line.toLowerCase().contains('groovy')) out << "File '$file' on line $num\n$line\n\n" } } }

File '..\files\src\PrintGroovySourceLines.groovy' on line 4 if (file.name.endsWith('.groovy')) { File '..\files\src\PrintGroovySourceLines.groovy' on line 6 if (line.toLowerCase().contains('groovy')) File '..\jdbc\src\JdbcGroovy.groovy' on line 1 import groovy.sql.Sql …

DSL example...

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Object.metaClass.please = { clos -> clos(delegate) } Object.metaClass.the = { clos -> delegate[1](clos(delegate[0])) } show = { thing -> [thing, { println it }] } square_root = { Math.sqrt(it) } given = { it } given 100 please show the square_root // ==> 10.0

...DSL example...

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Object.metaClass.of = { delegate[0](delegate[1](it)) } Object.metaClass.the = { clos -> [delegate[0], clos] } show = [{ println it }] square_root = { Math.sqrt(it) } please = { it } please show the square_root of 100 // ==> 10.0

...DSL example...

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show = { println it } square_root = { Math.sqrt(it) } def please(action) { [the: { what -> [of: { n -> action(what(n)) }] }] } please show the square_root of 100 // ==> 10.0

Inspiration for this example came from …

...DSL example

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// Japanese DSL using GEP3 rules Object.metaClass.を = Object.metaClass.の = { clos -> clos(delegate) } まず = { it } 表示する = { println it } 平方根 = { Math.sqrt(it) } まず 100 の平方根を表示する // First, show the square root of 100 // => 10.0

// source: http://d.hatena.ne.jp/uehaj/20100919/1284906117

// http://groovyconsole.appspot.com/edit/241001

Topics

• Intro

Functional Style

• Design Patterns

• Immutability

• Laziness

• GPars


• More Info

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• Recursion





• Concurrency

Show me the code

Example1.groovy






• Recursion





• Concurrency

Show me the code

Example2.groovy

Topics

• Intro


Design Patterns

• Immutability

• Laziness

• GPars


• More Info

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interface Calc { def execute(n, m) } class CalcByMult implements Calc { def execute(n, m) { n * m } } class CalcByManyAdds implements Calc { def execute(n, m) { def result = 0 n.times { result += m } return result } } def sampleData = [ [3, 4, 12], [5, -5, -25] ] Calc[] multiplicationStrategies = [ new CalcByMult(), new CalcByManyAdds() ] sampleData.each {data -> multiplicationStrategies.each {calc -> assert data[2] == calc.execute(data[0], data[1]) } }

def multiplicationStrategies = [ { n, m -> n * m }, { n, m -> def total = 0; n.times{ total += m }; total }, { n, m -> ([m] * n).sum() } ] def sampleData = [ [3, 4, 12], [5, -5, -25] ] sampleData.each{ data -> multiplicationStrategies.each{ calc -> assert data[2] == calc(data[0], data[1]) } }

Language features instead of Patterns

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Strategy Pattern

with interfaces

with closures

Adapter Pattern… class RoundPeg { def radius String toString() { "RoundPeg with radius $radius" } } class RoundHole { def radius def pegFits(peg) { peg.radius <= radius } String toString() { "RoundHole with radius $radius" } } def pretty(hole, peg) { if (hole.pegFits(peg)) println "$peg fits in $hole" else println "$peg does not fit in $hole" } def hole = new RoundHole(radius:4.0) (3..6).each { w -> pretty(hole, new RoundPeg(radius:w)) }

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RoundPeg with radius 3 fits in RoundHole with radius 4.0

RoundPeg with radius 4 fits in RoundHole with radius 4.0

RoundPeg with radius 5 does not fit in RoundHole with radius 4.0

RoundPeg with radius 6 does not fit in RoundHole with radius 4.0

…Adapter Pattern… class SquarePeg { def width String toString() { "SquarePeg with width $width" } } class SquarePegAdapter { def peg def getRadius() { Math.sqrt(((peg.width/2) ** 2)*2) } String toString() { "SquarePegAdapter with width $peg.width (and notional radius $radius)" } } def hole = new RoundHole(radius:4.0) (4..7).each { w -> pretty(hole, new SquarePegAdapter(peg: new SquarePeg(width: w))) }

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SquarePegAdapter with width 4 (and notional radius 2.8284271247461903)

fits in RoundHole with radius 4.0


fits in RoundHole with radius 4.0


does not fit in RoundHole with radius 4.0


does not fit in RoundHole with radius 4.0

…Adapter Pattern

SquarePeg.metaClass.getRadius = { Math.sqrt(((delegate.width/2)**2)*2) } (4..7).each { w -> pretty(hole, new SquarePeg(width:w)) }

SquarePeg with width 4 fits in RoundHole with radius 4.0

SquarePeg with width 5 fits in RoundHole with radius 4.0

SquarePeg with width 6 does not fit in RoundHole with radius 4.0

SquarePeg with width 7 does not fit in RoundHole with radius 4.0

Adapter Pattern

Do I create a whole new class

or just add the method I need

on the fly?

Consider the Pros and Cons!

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Further reading: James Lyndsay, Agile is Groovy, Testing is Square

Topics

• Intro


• Design Patterns

Immutability

• Laziness

• GPars


• More Info

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• Recursion





• Concurrency

Immutability options

• Built-in

• Google Collections – Numerous improved immutable collection types

• Groovy run-time metaprogramming

• Groovy compile-time metaprogramming

– @Immutable can help us create such classes

– Also gives us @Synchronized and @Lazy

import com.google.common.collect.* List<String> animals = ImmutableList.of("cat", "dog", "horse") animals << 'fish' // => java.lang.UnsupportedOperationException

def animals = ['cat', 'dog', 'horse'].asImmutable() animals << 'fish' // => java.lang.UnsupportedOperationException

def animals = ['cat', 'dog', 'horse'] ArrayList.metaClass.leftShift = { throw new UnsupportedOperationException() } animals << 'fish' // => java.lang.UnsupportedOperationException

@Immutable...

• Java Immutable Class – As per Joshua Bloch

Effective Java

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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 + ")"; } }

...@Immutable...

• Java Immutable Class – As per Joshua Bloch

Effective Java

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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

...@Immutable

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@Immutable class Person { String first, last }

Approaches to managing collection storage

• Mutable • Persistent

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• Immutable

‘c’ ‘a’ ‘c’ ‘a’ ‘c’ ‘a’

Add ‘t’ Add ‘t’ Add ‘t’

‘c’ ‘a’ ‘t’ ‘c’ ‘a’

‘c’ ‘a’ ‘t’

X ‘c’ ‘a’

‘t’

Persistent collections

• See also – Clojure (next)

– TotallyLazy (soon)

– Functional Java (tomorrow)

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@Grab('org.pcollections:pcollections:2.1.2') import org.pcollections.* PSet<String> set = HashTreePSet.empty() set += "something" println set println set + "something else" assert set.size() == 1 // => [something] // => [something, something else]

Clojure Libraries

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@Grab('org.clojure:clojure:1.0.0') import clojure.lang.* def ss = StringSeq.create('The quick brown fox') def done = false while (!done) { println ss.first() ss = ss.next() done = !ss }

'The quick brown fox'.each{ println it } <= Plain Groovy equivalent

Topics

• Intro


• Design Patterns

• Immutability

Laziness

• GPars


• More Info

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• Recursion





• Concurrency

Show me the code

TotallyLazyScript.groovy

GPars and TotallyLazy library

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@GrabResolver('http://repo.bodar.com') @Grab('com.googlecode.totallylazy:totallylazy:808') import static groovyx.gpars.GParsExecutorsPool.withPool import static com.googlecode.totallylazy.Callables.asString import static com.googlecode.totallylazy.Sequences.sequence withPool { pool -> assert ['5', '6'] == sequence(4, 5, 6) .drop(1) .mapConcurrently(asString(), pool) .toList() }

withPool { assert ['5', '6'] == [4, 5, 6] .drop(1) .collectParallel{ it.toString() } }

<= Plain GPars equivalent






• Recursion





• Concurrency

Memoization

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def plus = { a, b -> sleep 1000; a + b }.memoize() assert plus(1, 2) == 3 // after 1000ms assert plus(1, 2) == 3 // return immediately assert plus(2, 2) == 4 // after 1000ms assert plus(2, 2) == 4 // return immediately // other forms: // at least 10 invocations cached def plusAtLeast = { ... }.memoizeAtLeast(10) // at most 10 invocations cached def plusAtMost = { ... }.memoizeAtMost(10) // between 10 and 20 invocations cached def plusAtLeast = { ... }.memoizeBetween(10, 20)

Show me the code

Memoize.groovy, Factorial.groovy






• Recursion





• Concurrency

Show me the code

JScience, SPrintfChecker, GenericStackTest

Topics

Intro


• Design Patterns

• Immutability

• Laziness

GPars


• More Info

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• Recursion





• Concurrency

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

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http://strangeloop2010.com/talk/presentation_file/14485/Johnson-DataParallelism.pdf

Each approach has some caveats

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 1.5 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

– Safe Agents provide a non-blocking mt-safe reference to

mutable state; inspired by "agents" in Clojure

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Coordination approaches S

ou

rce

: R

eG

inA

– G

roovy in

Actio

n, 2

nd e

ditio

n

Data Parallelism:

Fork/Join

Map/Reduce

Fixed coordination

(for collections)

Actors Explicit coordination

Safe Agents Delegated coordination

Dataflow Implicit coordination

GPars: Choosing approaches F

or

mo

re d

eta

ils s

ee: h

ttp://g

pars

.co

de

ha

us.o

rg/C

once

pts

+co

mp

are

d

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

http://gpars.codehaus.org/Concepts+compared

http://gpars.codehaus.org/Concepts+compared

Groovy Sequential Collection

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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

GPars Parallel Collections…

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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 }

…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

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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 }

Parallel Collection Variations

• Apply some Groovy metaprogramming

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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 }

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 +

Transitive means result is automatically transparent; Lazy means fails fast

For

mo

re d

eta

ils s

ee R

eG

inA

or

the G

Pa

rs d

ocu

me

nta

tion

GPars: Map-Reduce

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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 }

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

For

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Parallel Collections vs Map-Reduce

Fork Fork

Join Join

Map

Map

Reduce

Map

Map

Reduce

Reduce

Map

Filter

Filter Map

Concurrency challenge…

• Suppose we have the following

calculation involving several functions:

• And we want to use our available cores …

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// 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

…Concurrency challenge…

• We can analyse the example’s task graph:

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// 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

a a

b

c

d

f

…Concurrency challenge…

• Manually using asynchronous functions:

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// 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

a a

b

c

d

f

…Concurrency challenge

• And with GPars Dataflows:

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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

a a

b

c

d

f

…Concurrency challenge

• And with GPars Dataflows:

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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

a a

b

c

d

f

GPars: Dataflows...

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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 }

5 10

y x

*

...GPars: Dataflows...

• Evaluating:

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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?


• Naive attempt for loops

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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


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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

...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

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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 }

…GPars: Actors...

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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



Software Transactional Memory…

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@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() } } // ...

…Software Transactional Memory

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// ... 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()

Topics

• Intro


• Design Patterns

• Immutability

• Laziness

• GPars

Word Split (bonus material)

• More Info

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Word Split with Fortress

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Guy Steele’s StrangeLoop keynote (from slide 52 onwards for several slides):

http://strangeloop2010.com/talk/presentation_file/14299/GuySteele-parallel.pdf

Word Split…

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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']

Word Split…

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Word Split…

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…Word Split…

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…Word Split…

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Segment(left1, m1, right1) Segment(left2, m2, right2)

Segment(left1, m1 + [ ? ] + m2, right2)

…Word Split…

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…Word Split…

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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) } }

…Word Split…

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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']

…Word Split…

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…Word Split…

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…Word Split…

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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() }

…Word Split…

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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() } }

…Guy Steele example in Groovy…

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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

…Guy Steele example in Groovy…

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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

…Guy Steele example in Groovy

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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

Topics

• Intro


• Design Patterns

• Immutability

• Laziness

• GPars


More Info

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More Information: Groovy in Action

Technology

Functional Groovy