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ptg -MartinBuchholz

JDKConcurrencyCzar,SunMicrosystems

-DoronRajwan

ResearchScientist,IntelCorp

userstoreadthisbook,covertocover. -TedNeward

AuthorofEffectiveEnterpriseJava

caresaboutperformance. -KirkPepperdine

CTO,JavaPerformanceTuning.com

showyouhowtodoit. -Dr.CliffClick

SeniorSoftwareEngineer,AzulSystems

Javadeveloperstoday.

-Dr.HeinzKabutz

TheJavaSpecialists"Newsletter

-BruceTate

AuthorofBeyondJava

easilyfoundelsewhere. -BillVenners

AuthorofInsidetheJavaVirtualMachine

ptgJava Concurrency in Practice ptgThis page intentionally left blank ptgJava Concurrency in PracticeBrian Goetzwith

Tim Peierls

Joshua Bloch

Joseph Bowbeer

David Holmes

and Doug LeaUpper Saddle River, NJ • Boston • Indianapolis • San Francisco New York • Toronto • Montreal • London • Munich • Paris • Madrid Capetown • Sydney • Tokyo • Singapore • Mexico City

ptgMany of the designations used by manufacturers and sellers to distinguish their products are claimed as trade-

marks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the

designations have been printed with initial capital letters or in all capitals.

The authors and publisher have taken care in the preparation of this book, but make no expressed or implied

warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental

or consequential damages in connection with or arising out of the use of the information or programs contained

herein.

The publisher offers excellent discounts on this book when ordered in quantity for bulk purchases or special

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vice@safaribooksonline.com. Library of Congress Cataloging-in-Publication Data

Goetz, Brian.

Java Concurrency in Practice / Brian Goetz, with Tim Peierls. . . [et al.] p. cm.

Includes bibliographical references and index.

ISBN 0-321-34960-1 (pbk. : alk. paper)

1. Java (Computer program language) 2. Parallel programming (Computer science) 3. Threads (Computer

programs) I. Title.

QA76.73.J38G588 2006

005.13"3--dc222006012205

Copyright © 2006 Pearson Education, Inc.Printing

9thMarch 2010Text printed in the United States on recycled paper at Courier Stoughton in Stoughton, Massachusetts.ISBN0-321-34960-1

ptgToJessica ptgThis page intentionally left blank ptgContentsListingsxii

Prefacexvii

1Introduction1

3SharingObjects33

4ComposingObjects55

ix ptgxContents

5BuildingBlocks79

7CancellationandShutdown135

8ApplyingThreadPools167

9GUIApplications189

11PerformanceandScalability221

ptgContentsxi

12TestingConcurrentPrograms247

14BuildingCustomSynchronizers291

16TheJavaMemoryModel337

16.1Whatisamemorymodel,andwhywouldIwantone? . .......337

AAnnotationsforConcurrency353

Bibliography355

Index359

2.1Astatelessservlet. . . . ..........................18

xii ptgListingsxiii ptgxivListings ptgListingsxv ptgxviListings

14.9Recloseable gate usingwaitandnotifyAll...............305

production,underheavyload. plicationsinJava.

WehopeyouenjoyJavaConcurrencyinPractice.

BrianGoetz

Williston,VT

March2006

xvii n.m],[CPJn.m],[JLSn.m],and[EJItemn]. bytheplatformlibraries. ptgPrefacexix insingle-threadedsubsystems. bothcorrectnessandperformance. //Neverreturnsthewronganswer!

System.exit(0);

}Listing1.Badwaytosortalist.Don"tdothis. sion. for(inti=0;i<1000000;i++) doNothing();

Collections.sort(list);

andfeedbackonthedraftAPIs. makethisbookbetter. improvements. fordoingtheillustrations.

TEX,LAT

andclasslibraries. other. 1 ptg2Chapter1.Introduction ofprograms. simultaneouslyonmultipleCPUs. ptg4Chapter1.Introduction someoverhead. points. allowedtousesynchronousI/O. environmentdoesnot. ptg6Chapter1.Introduction@NotThreadSafe publicclassUnsafeSequence{ privateintvalue; **Returnsauniquevalue.*/ publicintgetNext(){ returnvalue++; threadscouldcallgetNextandreceivethe same value.Figure1.1showshowthis differentthreads.UnsafeSequenceusesanonstandardannotation:@NotThreadSafe.This is one publicclassSequence{ @GuardedBy("this")privateintvalue; publicsynchronizedintgetNext(){ returnvalue++; ptg8Chapter1.Introduction single-threadedprograms. thatareintroducedbytheuseofthreads. costs. opingnon-thread-safeclasses. threads. plication. ptg10Chapter1.Introduction sharedobjects. simplyhavetobethread-safe. method. threadsafety. ptg1.4.Threadsareeverywhere11 eventthreadinstead. ptgThis page intentionally left blank ptgPartIFundamentals13 ptgThis page intentionally left blank mutablestate. externallyvisiblebehavior. Byshared,wemeanthat a variablecould be accessedbymultiple threads;by stillbrokenandmayfailatanymoment. 15 ptg2.1.Whatisthreadsafety?17 interactionsbetweenthethreads. anyotheractiononthecaller"spart. unsafeone?Whatdoweevenmeanby"safe"? definitionofcorrectness. frommultiplethreads. threadsafety. servletresponse.@ThreadSafe

BigIntegeri=extractFromRequest(req);

BigInteger[]factors=factor(i);

encodeIntoResponse(resp,factors);

2.2.@NotThreadSafe

privatelongcount=0; publiclonggetCount(){returncount;}

BigIntegeri=extractFromRequest(req);

BigInteger[]factors=factor(i);

++count; encodeIntoResponse(resp,factors);

Don"tdothis.

ptg20Chapter2.ThreadSafety byone. usedtomakeadecisiononwhattodonext.

Chapter16formoreondataraces.

ofthesystemmayhavechanged. codepath.@NotThreadSafe publicclassLazyInitRace{ privateExpensiveObjectinstance=null; publicExpensiveObjectgetInstance(){ if(instance==null) instance=newExpensiveObject(); returninstance; orusesthatvaluewhileyouareinmid-update. torizerinListing2.4.@ThreadSafe publiclonggetCount(){returncount.get();}

BigIntegeri=extractFromRequest(req);

BigInteger[]factors=factor(i);

count.incrementAndGet(); encodeIntoResponse(resp,factors); ptg24Chapter2.ThreadSafety variables?

Listing2.5.@NotThreadSafe

=newAtomicReference(); =newAtomicReference();

BigIntegeri=extractFromRequest(req);

if(i.equals(lastNumber.get())) else{

BigInteger[]factors=factor(i);

lastNumber.set(i); lastFactors.set(factors); encodeIntoResponse(resp,factors); icity.Don"tdothis. thatcouldmakeitproducethewronganswer. 15. ptg2.3.Locking25 //Accessormodifysharedstateguardedbylock guardedbythatlock. thelock,Awaitsforever. ptg26Chapter2.ThreadSafety bythe same lock.

ServletResponseresp){

BigIntegeri=extractFromRequest(req);

if(i.equals(lastNumber)) encodeIntoResponse(resp,lastFactors); else{

BigInteger[]factors=factor(i);

lastNumber=i; lastFactors=factors; encodeIntoResponse(resp,factors); grantedonaper-invocationbasis. publicsynchronizedvoiddoSomething(){ publicclassLoggingWidgetextendsWidget{ publicsynchronizedvoiddoSomething(){ super.doSomething(); thandoingsoconcurrently. ptg28Chapter2.ThreadSafety edByannotation. ptg2.5.Livenessandperformance29 program. ptg30Chapter2.ThreadSafetyALfactornU

BLfactormU

@GuardedBy("this")privatelonghits; @GuardedBy("this")privatelongcacheHits; return(double)cacheHits/(double)hits;

BigIntegeri=extractFromRequest(req);

BigInteger[]factors=null;

synchronized(this){ ++hits; if(i.equals(lastNumber)){ ++cacheHits; factors=lastFactors.clone(); if(factors==null){ factors=factor(i); synchronized(this){ lastNumber=i; lastFactors=factors.clone(); encodeIntoResponse(resp,factors); safetybenefit. ptg32Chapter2.ThreadSafety are"shortenough". 33
ptg34Chapter3.SharingObjects privatestaticbooleanready; privatestaticintnumber; publicvoidrun(){ while(!ready)

Thread.yield();

System.out.println(number);

publicstaticvoidmain(String[]args){ newReaderThread().start(); number=42; ready=true; zerobecause thewrite toreadymightbemadevisibletothereaderthreadbefore seeChapter16. cult. sharedvariablecanbearbitrarilystale. publicclassMutableInteger{ privateintvalue; publicintget(){returnvalue;} publicclassSynchronizedInteger{ @GuardedBy("this")privateintvalue; publicsynchronizedintget(){returnvalue;} ptg3.1.Visibility37Thread A

Thread B

Everything

before the unlock on M... ... is visible to everything after the lock on My = 1 lock M x = 1 unlock Mlock M i = x unlock M j = yFigure3.1.Visibilityguaranteesforsynchronization. ptg38Chapter3.SharingObjects architectures. while(!asleep) and howanobjectcanescape. ptg40Chapter3.SharingObjectsquotesdbs_dbs11.pdfusesText_17

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