principles of so3ware construc9on: objects, design, and ...charlie/courses/17-214/... · 4/12/2018...

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SchoolofComputerScience

PrinciplesofSo3wareConstruc9on: Objects,Design,andConcurrencyPart5:EtceteraJavalambdasandstreamsCharlieGarrod BogdanVasilescu

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Administrivia

•  Homework5BestFrameworksavailabletoday•  Homework5cdueMonday11:59p.m

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KeyconceptsfromTuesday

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Producer-consumerdesignpaSern

•  Goal:Decoupletheproducerandtheconsumerofsomedata•  Consequences:

–  Removescodedependencybetweenproducersandconsumers–  Producersandconsumerscanproduceandconsumeatdifferentrates

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ThemembranepaSern

•  Mul9pleroundsoffork-join,eachroundwai9ngforthepreviousroundtocomplete

Image from: Wikipedia

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Parallelprefixsumsalgorithm,upsweep

•  Computesthepar9alsumsinamoreusefulmanner

[13, 9, -4, 19, -6, 2, 6, 3]

[13, 22, -4, 15, -6, -4, 6, 9]

[13, 22, -4, 37, -6, -4, 6, 5]

[13, 22, -4, 37, -6, -4, 6, 42]

…

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Parallelprefixsumsalgorithm,downsweep

•  Nowunwindstocalculatetheothersums

[13, 22, -4, 37, -6, -4, 6, 42]

[13, 22, -4, 37, -6, 33, 6, 42]

[13, 22, 18, 37, 31, 33, 39, 42]

•  Recall,westartedwith:[13, 9, -4, 19, -6, 2, 6, 3]

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Doublingarraysizeaddstwomorelevels

Upsweep

Downsweep

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Fork/Join:computa9onalpaSernforparallelism

•  Forkataskintosubtasks•  Jointhesubtasks(i.e.,waitforthemtocomplete)•  Subtasksaredecomposedrecursively

•  Thejava.util.concurrent.ForkJoinPoolclass–  ImplementsExecutorService–  Executes java.util.concurrent.ForkJoinTask<V>or

java.util.concurrent.RecursiveTask<V>or java.util.concurrent.RecursiveAction

•  Thethreadsinthefork-joinpooldoworkstealing

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AForkJoinexample

•  SeePrefixSumsParallelForkJoin.java•  Seetheprocessorgo,gogo!

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Parallelprefixsumsalgorithm

•  Howgoodisthis?–  Work:O(n),Depth:O(lgn)

•  Compareto:PrefixSumsParallelArrays.java

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•  Compareto:PrefixSumsParallelArrays.java•  Comparetothesequen9alalgorithm:

–  SeePrefixSumsSequential.java

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•  Compareto:PrefixSumsParallelArrays.java•  Comparetothesequen9alalgorithm:

–  SeePrefixSumsSequential.java–  n-1addi9ons–  Memoryaccessissequen9al

•  Theparallelalgorithm:–  About2nusefuladdi9ons,plusextraaddi9onsfortheloopindexes–  Memoryaccessisnon-sequen9al

•  Thepunchline:–  Don'trollyourown–  CacheandconstantsmaSer–  Thebestparallelimplementa9onwasnobeSerthannaïvesequen9al

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Today

•  Javalambdasandfunc9onalinterfaces•  Javastreams

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Lambdas,briefly

•  Termcomesfromλ-Calculus–  Everythingisafunc9on!

•  Alambda(λ)isananonymousfunc9on

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DoesJavahavelambdas?

A.  Yes,it’shadthemsincethebeginningB.  Yes,it’shadthemsinceanonymousclasses(1.1)C.  Yes,it’shadthemsinceJava8—thespecsaysso!D.  No,neverhad’em,neverwill

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Func9onobjectsinJava1.0

classStringLengthComparatorimplementsComparator{privateStringLengthComparator(){}publicstaticfinalStringLengthComparatorINSTANCE=newStringLengthComparator();publicintcompare(Objecto1,Objecto2){Strings1=(String)o1,s2=(String)o2;returns1.length()-s2.length();}}Arrays.sort(words,StringLengthComparator.INSTANCE);

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Func9onobjectsinJava1.1

Arrays.sort(words,newComparator(){publicintcompare(Objecto1,Objecto2){Strings1=(String)o1,s2=(String)o2;returns1.length()-s2.length();}});

"ClassInstanceCrea9onExpression"(CICE)

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Func9onobjectsinJava5

Arrays.sort(words,newComparator<String>(){publicintcompare(Strings1,Strings2){returns1.length()-s2.length();}});

CICEwithgenerics

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Func9onobjectsinJava8

Arrays.sort(words,(s1,s2)->s1.length()-s2.length());

•  Theyfeellikelambdas,they’recalledlambdas

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Lambdasyntax

Syntax Exampleparameter->expression x->x*x

parameter->block s->{System.out.println(s);}

(parameters)->expression (x,y)->Math.sqrt(x*x+y*y)

(parameters)->block (s1,s2)->{System.out.println(s1+","+s2);}

(parameterdecls)->expression (doublex,doubley)->Math.sqrt(x*x+y*y)

(parametersdecls)->block (List<?>list)->{Arrays.shuffle(list);Arrays.sort(list);}

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Methodreferences:moresuccinctthanlambdas

•  Asta9cmethod–  e.g.,Math::cos

•  Anunboundinstancemethod(whosereceiverisunspecified)–  e.g.,String::length–  Theresul9ngfunc9onhasanextraargumentforthereceiver

•  Aboundinstancemethodofaspecificobject–  e.g.,System.out::println

•  Aconstructor–  e.g.,Integer::new,String[]::new

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Nofunc9ontypesinJava,onlyfunc3onalinterfaces

•  Interfaceswithonlyoneabstractmethod•  Op9onallyannotatedwith@FunctionalInterface•  Somefunc9onalinterfacesyouknow

–  java.lang.Runnable–  java.util.concurrent.Callable–  java.util.Comparator–  java.awt.event.ActionListener–  Many,manymoreinjava.util.function

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Func9oninterfacesinjava.util.function

BiConsumer<T,U>BiFunction<T,U,R>BinaryOperator<T>BiPredicate<T,U>BooleanSupplierConsumer<T>DoubleBinaryOperatorDoubleConsumerDoubleFunction<R>DoublePredicateDoubleSupplierDoubleToIntFunctionDoubleToLongFunctionDoubleUnaryOperatorFunction<T,R>IntBinaryOperatorIntConsumerIntFunction<R>IntPredicateIntSupplierIntToDoubleFunctionIntToLongFunction

IntUnaryOperatorLongBinaryOperatorLongConsumerLongFunction<R>LongPredicateLongSupplierLongToDoubleFunctionLongToIntFunctionLongUnaryOperatorObjDoubleConsumer<T>ObjIntConsumer<T>ObjLongConsumer<T>Predicate<T>Supplier<T>ToDoubleBiFunction<T,U>ToDoubleFunction<T>ToIntBiFunction<T,U>ToIntFunction<T>ToLongBiFunction<T,U>ToLongFunction<T>UnaryOperator<T>

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SomeFunction<String,Integer>

Descrip<on CodeLambda s->Integer.parseInt(s)

Lambdaw/explicitparamtype (Strings)->Integer.parseInt(s)

Sta9cmethodreference Integer::parseInt

Constructorreference Integer::new

Instancemethodreference String::length

AnonymousclassICE newFunction<String,Integer>(){publicIntegerapply(Strings){returns.length();}}

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Javastreams

•  Astreamisabunchofdataobjects,typicallyfromacollec9on,array,orinputdevice,forprocessing

•  Processedbyapipeline–  Asinglestreamgenerator(datasource)–  Zeroormoreintermediatestreamopera.ons–  Asingleterminalstreamopera.on

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Streamexamples:Itera9on

//IterationoveracollectionstaticList<String>stringList=...;stringList.stream().forEach(System.out::println);//IterationoverarangeofintegersIntStream.range(0,10).forEach(System.out::println);//Aminipuzzler:whatdoesthisprint?"Helloworld!".chars().forEach(System.out::print);

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Puzzlersolu9on

"Helloworld!".chars().forEach(System.out::print);

Prints"721011081081113211911111410810033"

ThecharsmethodonStringreturnsanIntStream

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Howdoyoufixit?

"Helloworld!".chars().forEach(x->System.out.print((char)x));

•  Nowprints"Helloworld!"

•  Morals:–  Streamsonlyforobjectreftypes,int,long,anddouble–  Typeinferencecanbeconfusing

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Streamexamples:mapping,filtering

List<String>longStrings=stringList.stream().filter(s->s.length()>42).collect(Collectors.toList());

List<String>firstLetters=stringList.stream().map(s->s.substring(0,1)).collect(Collectors.toList());

List<String>firstLetterOfLongStrings=stringList.stream().filter(s->s.length()>42).map(s->s.substring(0,1)).collect(Collectors.toList());

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Streamexamples:duplicates,sor9ng

List<String>dupsRemoved=stringList.stream().map(s->s.substring(0,1)).distinct().collect(Collectors.toList());List<String>sortedList=stringList.stream().map(s->s.substring(0,1)).sorted()//Bufferseverythinguntilterminalop.collect(Collectors.toList());

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Streamexamples:bulkpredicates

booleanallStringHaveLengthThree=stringList.stream().allMatch(s->s.length()==3);booleananyStringHasLengthThree=stringList.stream().anyMatch(s->s.length()==3);

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Streamsareprocessedlazily

•  Dataispulledbyterminalopera9on,notpushedbysource–  Infinitestreamsarenotaproblem

•  Intermediateopera9onscanbefused–  Mul9pleintermediateopera9onsusuallydon’tcausemul9pletraversals

•  Intermediateresultsusuallynotstored–  Butthereareexcep9ons(e.g.,sorted)

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Easyparallelism:.parallelStream()

List<String>longStrings=stringList.parallelStream().filter(s->s.length()>42).collect(Collectors.toList());

List<String>firstLetters=stringList.parallelStream().map(s->s.substring(0,1)).collect(Collectors.toList());

List<String>firstLetterOfLongStrings=stringList.parallelStream().filter(s->s.length()>42).map(s->s.substring(0,1)).collect(Collectors.toList());

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Streaminterfaceisamonster(1/3)

publicinterfaceStream<T>extendsBaseStream<T,Stream<T>>{//IntermediateOperationsStream<T>filter(Predicate<T>);<R>Stream<R>map(Function<T,R>);IntStreammapToInt(ToIntFunction<T>);LongStreammapToLong(ToLongFunction<T>);DoubleStreammapToDouble(ToDoubleFunction<T>);<R>Stream<R>flatMap(Function<T,Stream<R>>);IntStreamflatMapToInt(Function<T,IntStream>);LongStreamflatMapToLong(Function<T,LongStream>);DoubleStreamflatMapToDouble(Function<T,DoubleStream>);Stream<T>distinct();Stream<T>sorted();Stream<T>sorted(Comparator<T>);Stream<T>peek(Consumer<T>);Stream<T>limit(long);Stream<T>skip(long);

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//TerminalOperationsvoidforEach(Consumer<T>);//OrderedonlyforsequentialstreamsvoidforEachOrdered(Consumer<T>);//OrderedifencounterorderexistsObject[]toArray();<A>A[]toArray(IntFunction<A[]>arrayAllocator);Treduce(T,BinaryOperator<T>);Optional<T>reduce(BinaryOperator<T>);Ureduce(U,BiFunction<U,T,U>,BinaryOperator);<R,A>Rcollect(Collector<T,A,R>);//MutableReductionOperation<R>Rcollect(Supplier<R>,BiConsumer<R,T>,BiConsumer<R,R>);Optional<T>min(Comparator<T>);Optional<T>max(Comparator<T>);longcount();booleananyMatch(Predicate<T>);booleanallMatch(Predicate<T>);booleannoneMatch(Predicate<T>);Optional<T>findFirst();Optional<T>findAny();

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//Staticmethods:streamsourcespublicstatic<T>Stream.Builder<T>builder();publicstatic<T>Stream<T>empty();publicstatic<T>Stream<T>of(T);publicstatic<T>Stream<T>of(T...);publicstatic<T>Stream<T>iterate(T,UnaryOperator<T>);publicstatic<T>Stream<T>generate(Supplier<T>);publicstatic<T>Stream<T>concat(Stream<T>,Stream<T>);}

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Incaseyoureyesaren’tglazedyet

publicinterfaceBaseStream<T,SextendsBaseStream<T,S>>extendsAutoCloseable{

Iterator<T>iterator();Spliterator<T>spliterator();booleanisParallel();Ssequential();//MayhavelittleornoeffectSparallel();//MayhavelittleornoeffectSunordered();//Noteasymmetrywrtsequential/parallelSonClose(Runnable);voidclose();}

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Itkeepsgoing:java.util.stream.Collectors

...toList()

...toMap(...)

...toSet(...)

...reducingBy(...)

...groupingBy(...)

...partitioningBy(...)...

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Optional<T>:anotherwaytoindicatetheabsenceofaresult

ItalsoactsabitlikeadegeneratestreampublicfinalclassOptional<T>{booleanisPresent();Tget();

voidifPresent(Consumer<T>);Optional<T>filter(Predicate<T>);Optionalmap(Function<T,U>);OptionalflatMap(Function<T,Optional>);TorElse(T);TorElseGet(Supplier<T>);<XextendsThrowable>TorElseThrow(Supplier<X>)throwsX;}

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Streamprac9ce

•  GivenaList<String>words,usestreamsto:–  GenerateaList<String>ofallwordscontainingthesubstring"heat"–  Determineifanywordcontainsthesubstring"aoeu"(aboolean)

•  Challenge:Convertsomeopera9oninyourCarcassonnesolu9ontousestreams…

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Streamparallelism:Yourmileagemayvary

•  Considerthisfor-loop(.96srun9me;dual-corelaptop)longsum=0;for(longj=0;j<Integer.MAX_VALUE;j++)sum+=j;

•  Equivalentstreamcomputa9on(1.5s)longsum=LongStream.range(0,Integer.MAX_VALUE).sum();

•  Equivalentparallelcomputa9on(.77s)longsum=LongStream.range(0,Integer.MAX_VALUE).parallel().sum();

•  Carefullyhandcra3edparallelcode(.48s)

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Whentouseaparallelstream,looselyspeaking

•  Whenopera9onsareindependent,and•  Eitherorboth:

–  Opera9onsarecomputa9onallyexpensive–  Opera9onsareappliedtomanyelementsofefficientlyspliSabledata

structures–  Roughly:Numberofelements*Cost/element>>10,000

•  AlwaysmeasurebeforeandaDerparallelizing!

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Whennotto…

•  Useaparallelstream…•  Useastream...

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Summary

•  APIdesign:"Funandeasytolearnanduse…?"•  Whentousealambda

–  Always,inpreferencetoCICE•  Whentouseamethodreference

–  Almostalways,inpreferencetoalambda•  Whentouseastream

–  Whenitfeelsandlooksright•  Whentouseaparallelstream

–  Numberofelements*Cost/element>>10,000•  Keepitclassy!

–  Javaisnotafunc9onallanguage

principles of so3ware construc9on: objects, design, and ...charlie/courses/17-214/... · 4/12/2018...

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