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1、ContextObjectADesignPatternforEfficientInformationSharingacrossMultipleSystemLayersArvindS.Krishna,DouglasC.SchmidtMichaelStalElectricalEngineering&ComputerScienceSiemensAGCorporateTechnologyVanderbiltUniversity,Nashville,TNMunich,Germany{arvindk,schmidt}@dre.vanderbi
2、lt.edumichael.stal@siemens.comAbstractSoftwaresystemswithalayeredarchitecture,suchasmid-dleware,needtopropagate/shareinformationacrossthedifferentsystemlayers.Inmiddlewareforexample,effi-cientinformationsharingacrossdifferentmiddlewarelay-ersenablestimelyprocessingofc
3、lientrequests;acriticalmiddlewarefunctionalityThispaperpresentstheContextObjectpatternthatallowsefficientprocessingofrequestsbypropagatingcontextinformationbetweendifferentmid-dlewarelayers.Usingthispattern,alayer/sessionpropa-gatesper-requestinformationrequiredbythen
4、extlayer/sessioninacontextobject,whicheliminatestheneedfor(1)per-requeststatewithineachlayerand(2)lock-ing/synchronizationtoaccessper-requestinformationacrossdifferentlayers.ThispatternisusedinCORBAObjectRequestBrokers(ORBs)forrequestprocessing.1IntentThispatternprovi
5、desanefficient,andapplication-transparentwayofsharinginformationbetweendifferentlayersinasoftwaresystem.Figure1.LayeredCORBARequestProcessingInourexample,asshowninFigure1(anddiscussedin2ExampleAppendixA),requestprocessingsteps1-2arecarriedoutManyapplicationsusemiddlew
6、aretoshieldthemfromintheI/Olayer,steps3-5arecarriedoutintheORBcoresystem-specificissues,suchascommunicationprotocols,layer,andstep6isexecutedintheobjectadapterlayer.Inconcurrencystrategies,(de)multiplexingstrategies,oraddition,eachlayerrequiressomeinformationprocessed
7、(de)marshalingmechanisms.Thistransparencyhelpsde-byalayerdirectlybeneathit.Forexample,thenameofthevelopersfocusonapplicationneeds,ratherthanwrestlingoperationdemarshaledintheI/Olayerisrequiredinthewithlow-leveldistributiondetailsexplicitlyandmanually.objectadapterlaye
8、rtoperformtheupcall.Similarly,aToprovidethedifferentmiddlewarefunctionalities,mid-messageparserassociatedintheORBcorelayeris
