Certain investigations on performance enhancement of stub code in corba based applications

Abstract

VABSTRACTDistributedObjectSystemsprovideanexcellentsupportforevolutionarydevelopmentofsoftwarefordistributedapplicationsthroughsoftwarereuse.RequestbrokerslikeCommonObjectBrokerArchitecture(CORBA)shieldtheapplicationdevelopersfromlow-level,tediousanderrorproneplatformdetails.Theyprovideplatform,language,network,hardware,protocolandobjectlocationtransparencybyincludinganabstractionlayerbetweentheapplicationprogramsandthenetworkingprotocols.JavaRemoteMethodInvocation(RMI)islanguagedependentandDistributedComponentObjectModel(DCOM)isplatformdependent.ButCORBAistransparenttoprogramminglanguageandplatform.CORBAusesGeneralInteroperableProtocol(GIOP)asitscommunicationprotocol.Itfitsintotheapplication,presentationandsessionlayersintheOpenSystemsInterconnection(OSI)model.Presentationconversiondealswiththeconversionofdatafromlocalmachinerepresentationtoacommonnetworkformat.ThisprocessofmarshallingiscarriedoutusingstaticstubsgeneratedbytheInterfaceDefinitionLanguage(IDL)compilerorgenericdynamicstubs.ThestubcodegeneratedfromtheIDLtakescareofmarshallingtherequeststransparentlytotheuser.MajorlimitationsofcoreCORBAincludelackofselectiveinheritance,creation/destructionoftheobjectsbytheclientandinefficientmarshalling,alignandcheck,bufferinganddatacopyingprocedures.AlsoCORBAlackssupportforgenerationoftime-efficientandcompactstubcode.OtherinefficienciesinCORBAincludeThemajorobjectiveofthisthesisistostudy,analyseandproposemethodstoenhancetheperformanceofstubcode.Theresearchworkisfocusedonthefollowingissues:•EnhancementsonCORBAstandard:1.AmethodtoachieveselectivemultipleinheritanceinCORBAstatically. VISelectivemultipleinheritancecannotbedirectlyimplementedinCORBA,becausefunctionredefinitionisnotallowedinderivedinterface.AmethodusingconditionalinterfacestoimplementselectivemultipleinheritanceinCORBAisproposed.Thisusesacontainerclassderivedfromthebaseinterfacebasedonthecondition.2.AmethodforcreationanddestructionofCORBAobjectsusingabaseinterface.DeactivationoftheCORBAobjectoccurswhentheserverterminates.Thisleadstounder-utilizationofresources.Henceabaseinterfacewithoperationsforreferencecounting,instantiationand destructionofCORBA objectsisimplemented.•IdentificationofthecommonsourcesofoverheadinmarshallinginCORBA-basedapplications.•Improvementsintheefficiencyofmarshallingusingthefollowingapproaches:1. Incorporatingchangesinthetransmissionmedium.2.Introducingnewencodingrulestotakecareofreductionofsizeofthedatapassedinthenetworkandthemarshallingtime.3.Improvingthesecurityinlinklevelcommunicationofthemarshaleddata.4.Optimisedencode/decodesoftwaretogeneratetime-efficientandcompactencoding/decodingmarshallingroutines.CommonsourcesofoverheadinmarshallinginCORBA-based applicationshavebeenidentified.Thisincludesinefficientalignandcheck, multiplexinganddatacopyingalgorithmswhichreducesthespeedofInternet InteroperableProtocol(HOP),presenceofextrapaddingbytesinCommon DataRepresentation(CDR)foralignmentandlackoftime-efficientandcompactstubcode.Basedonthisstudy,changeswereproposedinthetransmissionmedium,encodingformatandencodingproceduresinCORBA. VllHOPisthetransmissionmediumforCORBAbasedapplications. Thoughitbringsaboutinteroperability,itisslow.Hencechangesinthetransmissionmediumtoimprovetheperformanceofthestubcodehavebeenproposed.Toachievethis,componentizedIDLcompilerisdesigned.Ithasthreephases-frontend,presentationgeneratorandbackend.Thebackendofthecompilergeneratesstubsandskeletonsforaparticulartransmissionmechanismandmessageformat.ConventionalCORBAstubsuseTCP/IP socketsoverHOP.Sinceitisslow,modulesareincorporatedinthebackendtoproducestubswithfasterIPCmechanismslikesharedmemory,multiplesharedmemorysegments,threadingmultiplesharedmemorysegments,socketsover TCP/IPandmultiplesockets.ThecomponentizeddesignoftheIDLcompilerfacilitatestheusageofmultipleIDLs,backendsandtargetlanguages.Usingthismodel,interoperabilitybetweenCORBAandRMIusingRMI/IIOPisachieved.AstaticbridgebetweenCORBAandCOMhasbeenimplementedusingthismodel.Encodingmechanismsalsoinfluencetheefficiencyofpresentationcode.CORBAusesCommonDataRepresentation(CDR)mechanismtoencodedata.SinceCDRusesexcessivealignmentatthewordboundaries,newencodingrulestogenerateefficientstubcodehavebeenproposed.Thisincludes thefollowing:1)Representationofbooleandatainbitformatinanarray.2) Removingthealignmentatthenaturalwordboundariestoeliminate theextrapaddingbytes.3)Correctallocationofthesendandreceivebufferspacedependinguponthesizeofthedatabeingtransmitted.4)ReorderingofparametersinthedescendingorderofsizetoreducethenumberofpaddingbitsinCDR.5)AnovellinklevelencryptionschemetobringaboutsecurityinCORBAbasedapplicationshasbeenproposed.Encryptionisperformedbychoosingasetoffunctionsfromadomainoffunctionsbasedon vinvalidation.Thevalidationprocessisdonebymappingeverybitoftheplaintextblocktoabasestringforamatch.Fasterandcompactencodingproceduresbyoptimizingtheimplementationoftheencode/decodesoftwarehavebeenproposed.Thetechniquesusedtoimplementpresentationconversionroutinescanbeinterpretedandproceduredriven.Interpretedroutinesresultinsmallercode,whileprocedure-drivenroutinesexecutefaster.Sothelatercanbeusedformorefrequentlyoccurringtypes.AnoptimizerimplementedinthepresentationgenerationstageoftheIDLcompilergeneratesahybridstubcode.Itachievesabalancebetweencodesizeandexecutionspeedofthestubcode.Theoptimizerusessingleandmultipleobjectivegeneticalgorithms.ThesuitabilityofMultipleObjectiveCross-overMutation,SelfReproductionMutation(MOCM-SRM)andGeneticLocalSearch(GLS)methodshavebeenstudied.ParallelimplementationofMOCM-SRMmethodhasbeenidentifiedtobesuitable.Theperformanceofthehybridstubcodegeneratedusingthisapproachhasbeeninvestigated.Further,CORBAtreatsDllandSllastwodifferentinvocationmechanisms.Sllstubslikecompiled,interpretedandinlinedcompilationdifferintheircodesizeandexecutionspeed.Sotheproposedmethodisextendedtogenerateahybridizedstubcodetostrikeabalancebetweenthesefourinvocationmechanisms.Sincepresentationconversionisanexpensivepartofnetworkcommunication,thefollowingmethodsareimplementedtoimprovetheefficiencyofpresentationlayerconversion:1.EfficientIPCmechanismslikesharedmemory,multiplesegmentsofsharedmemory,threadedsharedmemorysegmentsandmultiplesocketswereimplemented2.Efficienthybridstubcodewasgeneratedbyoptimizingtheencoder/decodersoftwareconsideringstaticanddynamicfrequencyofthedatatypes.3.ChangeswereimplementedintheencodingmechanismofCORBA.ThefollowingapproacheswereusedtoimprovetheefficiencyofencodinginCORBA: IX•Representationofthebooleanarraysinbitformat.•Removalofthe extrapaddingbitsinCDR.•Reorderingtheparametersinthedescendingorderoftheirsizetominimizethenumberofpaddingbytes.• ImplementingsecurecommunicationbetweenCORBAobjectsatthelinklevelusinganovelsymmetrickeyencryptionmethod.