Efficient implementations of Java remote method in

EcientImplementationsofJavaRemoteMethodInvocation(RMI)VijaykumarKrishnaswamyDanWaltherSumeerBholaEthendranathBommaiahGeorgeRileyBradTopolMustaqueAhamadyCollegeofComputingGeorgiaInstituteofTechnologyAtlanta,GA30332AbstractJavaandtheRemoteMethodInvocation(RMI)mechanismsupportedbyitmakeiteasytobuilddistributedapplicationsandser-vicesinaheterogeneousenvironment.Whentheapplicationsareinteractiveandrequirelowresponsetime,ecientimplementationsofRMIareneeded.Weexplorebothtrans-portlevelprotocolsaswellasobjectcachingintheRMIframeworktomeettheperfor-mancerequirementsofinteractiveapplica-tions.Wehavedevelopedaprototypesystemthatoersnewtransportprotocolsandallowsobjectstobecachedatclientnodes.Wede-scribethedesignissuesandtheimplementa-tionchoicesmadeintheprototypealongwithsomepreliminaryperformanceresults.1IntroductionInteractiveapplicationsthatenablewidelydistributeduserstocooperateovertheInter-netwillbecomeincreasinglycommoninthefuture.SuchapplicationshavetraditionallybeenexploredintheareaofgroupwarebutasincreasedbandwidthsbecomeavailableintoThisworkwassupportedinpartbyNSFgrantsCDA-9501637andCCR-9619371,andindustrialpart-nersoftheBroadbandTelecomCenter,GeorgiaIn-stituteofTechnology.yContactauthor:Emailandhomepage{[e-mail],(e.g.,cableanddigitalsubscriberline(xDSL)networks),electroniccommerceandentertainmentapplicationswillbecomeinteractive.Forexample,aconsumerlocatedathomecanutilizeagraphicaluserinterface(GUI)toviewvariousretailitemsheorsheisinterestedinpurchasing.Simultaneously,asalesassociatelocatedattheretailoutletmayalsohaveacopyoftheGUIwhichper-mitstheassociatetoseewhatthecustomerisselectingandmaysuggestalternativeswhicharethenpresentedinthecustomer’sGUI.Furthermore,thehomeconsumermayhaverequestedfriendslocatedatotherhomestoalsoparticipateinthisdecisionmakingandthereforetheytoomayberunningaGUIandviewingthepossibilitiesandalsomakingsug-gestions.Manysuchinteractiveapplicationscenarioscanbeconstructedeasily.Interactiveapplicationswillbesupportedbyshareddistributedservices.Inorderfortheinternetworkedcomputinginfrastructuretosupporttheaboveapplicationscenario,systemsupportisneededtoallowthedis-tributedservicesandclientapplicationstobeprogrammedeasily.Theuseofobjecttech-nologyisbecominganincreasinglypopularapproachforimplementingdistributedser-vices.Thisisduetothefactthatobjecttechnologyprovidesauniformmechanismforaccessinglocalandremoteresourcesandre-ducesthecomplexityofbuildingapplicationsinaninternetworkedcomputingenvironment.TheJavalanguageisapopularfoundationforbuildingdistributedservicesandappli-cationsbecauseithidestheproblemsthatariseduetoheterogeneityofserverandclienthardwareandsoftwareplatforms.RemoteMethodInvocation(RMI)isJava’smecha-nismforsupportingdistributedobjectbasedcomputing[18].RMIallowsclient/serverbaseddistributedapplicationstobedevel-opedeasilybecauseaclientapplicationrun-ninginaJavavirtualmachineatonenodecaninvokeobjectsimplementedbyaremoteJavavirtualmachine(e.g.,aremoteservice)thesamewayaslocalobjects.AlthoughRMIenhancestheeaseofpro-grammingfordistributedapplications,wehavefoundthatitdoesresultinsignicantperformancepenaltiesforapplicationscom-paredtomessagepassing[10].Suchlossofperformanceisundesirableforinteractiveap-plicationsinawide-areaenvironmentbecauseoftheneedforinteractiveresponsetimeinthepresenceofhighcommunicationlaten-cies.TheadditionalprocessingrequiredbyRMIwilladdsomeoverheadcomparedtomessagepassingbutthereareanumberoftechniquesthatcanexploitthecommunica-tionstructureembodiedbyRMItoprovidebetterperformance.Forexample,itmaybepossibletoexploitthe\invocation-responsenatureofRMIcommunicationstodevelopamoreecientcommunicationprotocolthantheTCPprotocolthatisemployedbyRMI(suchanapproachwasusedintheimple-mentationofremoteprocedurecallorRPC[2]whichiscloselyrelatedtoRMI).Further-more,whenpossible,aclientmaybeabletocachethestateofremoteobjectsandinvokethemlocally.Inthiscase,theoverheadas-sociatedwithcommunicationcanbeavoidedwhenthereissignicantlocalityofaccess.Weexploreanumberoftechniquestoim-proveRMIperformanceandintegratethemintotheRMIframework.Sincetheperfor-manceofRMIdependsontheunderlyingcommunicationprotocols,werstexploreanumberofalternatetransportsthatmayim-provetheperformanceofRMIimplementa-tions.Wedevelopedauserdatagrampro-tocol(UDP)basedreliablemessagedeliveryprotocolthatexploitstherequest-responsenatureofRMIcommunications.Also,whenobjectstateiscachedatclientnodes,con-sistencyofthereplicatedobjectcopieshastobemaintained.Consistencyprotocolsforreplicatedobjectscanbenetfromone-to-many(e.g.,multicast)communicationandwehavedevelopedaexiblemulticasttransportthatisavailabletoRMIimplementation.Fi-nally,weextendthereferencelayerintheRMIframeworktocacheobjectsatclientnodes.Thisapproachallowsclientstotrans-parentlyinvokeremoteobjectsindependentofwhethertheyarebeingcached.Whenacachedcopyofaninvokedobjectisavailable,theinvocationisexecutedlocally.Aninvali-dationbasedprotocolhasbeenimplementedtomaintainconsistencyofthecac