Concurrent C++ Concurrent Programming With Class.docx

Concurrent C++ Concurrent Programming With Class.docx

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ConcurrentC++ConcurrentProgrammingWithClass

ConcurrentC++:

ConcurrentProgrammingWithClass（es）

N.H.Gehani

W.D.Roome

AT&TBellLaboratories

MurrayHill,NewJersey07974

1.Introduction

Recentlytwoupward-compatibleextensionsoftheCprogramminglanguage[Kernighan1978]havebeen

developed:

ConcurrentC[Gehani&Roome1986;Cmelik,Gehani&Roome1987]whichprovidesparallel

programmingfacilities,andC++[Stroustrup1986],whichprovidesdataabstractionfacilities.C++does

notprovideparallelprogrammingfacilities,andConcurrentCdoesnotprovidedataabstractionfacilities.

Althoughdataabstractionfacilitiesareimportantforwritingconcurrentprograms,wedidnotprovidethem

inConcurrentCbecausewedidnotwanttoduplicatetheC++researcheffort.Instead,wedecidedthatwe

wouldeventuallyintegrateC++andConcurrentCfacilitiestoproducealanguagewithbothdata

abstractionandparallelprogrammingfacilities:

ConcurrentC++.Thiswasapragmaticdecision.Wefelt

thatitwouldbebetterifConcurrentC++hadthesamedataabstractionasC++becausethiswouldmake

ConcurrentC++upwardcompatiblewithC++andConcurrentC++wouldthenbemoreattractiveforC++

usersinterestedinwritingconcurrentprograms.

Havinggainedexperienceinbothlanguages,wedecidedtomergeC++andConcurrentCtoproduce

ConcurrentC++.Dataabstractionandparallelprogrammingfacilitiesareorthogonal.Despitethis,the

mergerofConcurrentCandC++raisedseveralintegrationissues.Inthispaper,wewillgivebrief

introductionstoC++andConcurrentCandthenpresenttwoexamplesofhowclasses,thedataabstraction

facilityofC++,canbevaluableforwritingconcurrentprograms.Afterthiswewilldiscusstheissuesin

integratingC++andConcurrentCandthendescribethecurrentstateofaffairs.

2.BriefSummaryofC++

TheC++dataabstractionfacilityiscalledtheclass.Classdeclarationsconsistoftwoparts:

aspecification

andabody.Theclassspecificationrepresentstheclass‘‘userinterface’’.Itcontainsalltheinformation

necessaryfortheuserofaclass.Theclassspecificationalsocontainsinformationnecessaryforthe

compilertoallocateclassobjects.Theclassbodyconsistsofbodiesoffunctionsdeclaredintheclass

specificationbutwhosebodieswerenotgiventhere.Intherestofthissection,wewillgiveabrief

overviewoftheC++classfacility.Foradetailedexplanation,seeTheC++ProgrammingLanguage

[Stroustrup1986].

Classspecificationshavetheform

classname{

privatecomponents



publiccomponents

};

Theprivatecomponentsofaclassaredataitemsandfunctionsthatimplementclassobjects.These

representinternaldetailsoftheclassandcannotbeaccessedbytheuserofaclass.

Thepublicclasscomponentscanbedataitems,constructors,destructors,memberfunctions（operators）,

andfriendfunctions（operators）.Thepubliccomponents（tobeprecise）representtheclassuserinterface.

Thesearethecomponentsthattheuserofaclasscanuseorcall.Constructorsarefunctionsthatarecalled

automaticallytoconstructaclassvalue.Destructorsarealsofunctionsthatarecalledautomaticallywhen

thescopeofaclassobjectisleft;theyareintendedforperforming‘‘cleanup’’chores.Memberandfriend

functionsarefunctionsthatareusedtomanipulateclassobjects.1Notethatoperatorscanbe‘‘overloaded’’

⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

public:







⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

-2-

inC++.

Asanexampleofclasses,considertheclasscomplex:

⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

classcomplex{

doublere,im;



complex（doubler,doublei）;

complex（doubler）;

complex（）;



doublereal（）;

doubleimag（）;



friendcomplexoperator+（complex,complex）;

friendcomplexoperator-（complex,complex）;

friendcomplexoperator-（complex）;

friendcomplexoperator*（complex,complex）;

friendcomplexoperator/（complex,complex）;

friendintoperator==（complex,complex）;

friendintoperator!

=（complex,complex）;

};

Thefirstthreelinesinthepublicpartofthecomplexclassshownabovearedeclarationsofconstructors.

Anappropriateconstructor,selectedaccordingtotheinitializationvaluessupplied,isautomaticallycalled

whencomplexvariablesaredefined.Thenextlinedeclaresthememberfunctionsrealandimag,and

theremaininglinesdeclarefriendoperators.

Wewillshowthedefinitionsofoneconstructorfunction,onememberfunctionandonefriendoperator.

#include"complex.h"

complex:

:

complex（doubler,doublei）

{



re=r;im=i;

}



doublecomplex:

:

real（）

{

returnre;

}



complexoperator+（complexa,complexb）

{

returncomplex（a.re+b.re,a.im+b.im）;

}

Herearesomeexamplesillustratingusesofthecomplexclass:

__________________

1.Inthispaper,weshallnotdistinguishbetweenmemberandfriendfunctionsexcepttosaythattheirsyntaxisslightlydifferent.





public:















































⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽









⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

File:

complex.h

-3-

⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽⎽

complexa=complex（5.0,6.0）,b=complex（1.0,1.0）;











c=a+b;

Notethatforillustrationpurposes,variablesaandbhavebeeninitializedexplicitlyandvariablechasnot

beenexplicitlyinitialized.Forvariablesaandb,thefirstconstructorshownisautomaticallyinvokedto

constructtheinitialvalue,andforvariablecthethirdconstructorisinvokedtoconstructthedefaultinitial

value.Theconstructorinvokeddependsupontheinitialargumentssupplied（ornotsupplied）when

definingaclassvariable.

3.BriefSummaryofConcurrentC

AConcurrentCprogramconsistsofasetofcomponents,calledprocesses,thatexecuteinparallel.

ConcurrentCprovidesfacilitiesfordeclaringandcreatingprocesses,processsynchronizationand

interaction,processterminationandabortion,priorityspecificationandwaitingformultipleevents,

amongstotherthings.

ConcurrentCprocessesinteractwitheachotherbymeansoftransactions.Transactionsareassociatedwith

processesandthesemaybethoughtofasservicesthatarecalled（used）byotherprocesses.Processes

callingservicesmaybethoughtofas‘‘client’’processesandprocessesoffering（andaccepting）services

maybethoughtofas‘‘server’’processes.Weshallusetheterms‘‘calling’’and‘‘client’’,andtheterms

‘‘called’’and‘‘server’’processesinterchangeably.Therearetwokindsoftransactions:

synchronous（or

blocking）andasynchronous（ornonblocking）.Thecallingprocesssendsinformationtotheserverprocess

bymeansoftransactionparameters,andincaseofsynchronoustransactioncalls,thecalledprocesscan

returninformationtothecallingprocessasthetransactionresult.

Aprocesscallingasynchronoustransactionisblockeduntilthecalledprocessacceptsthetransaction

（givestherequestedservice）,executesthecodeassociatedwiththetransaction,andreturnsthetransaction

result,ifany.Synchronoustransactionsallowbidirectionalcommunicationbetweentheinteracting

processes.Synchronoustransactioncallscanalsobeusedforprocesssynchronization:

thecallingand

receivingprocesssynchronizeatthetransactioncall.Theyarefreetoresumeindependentoperationafter

thetransactioncallhasbeenaccepted.Infact,transactioncallscanbeusedjustforsynchronization（a

transactionneednothaveanyparametersanditcanhavethevoidresulttype）.

Aprocesscallinganasynchronoustransactionisallowedtocontinueimmediatelyaftermakingthecall.

Thetransactionisacceptedbythecalledpro