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1、ContextObjectADesignPatternforEfficientInformationSharingacrossMultipleSystemLayersArvindS.Krishna,DouglasC.SchmidtMichaelStalElectricalEngineering&ComputerScienceSiemensAGCorporateTechnologyVanderbiltUniversity,Nashville,TNMunich,Germany{arvindk,schm
2、idt}@dre.vanderbilt.edumichael.stal@siemens.comAbstractSoftwaresystemswithalayeredarchitecture,suchasmid-dleware,needtopropagate/shareinformationacrossthedifferentsystemlayers.Inmiddlewareforexample,effi-cientinformationsharingacrossdifferentmiddlewar
3、elay-ersenablestimelyprocessingofclientrequests;acriticalmiddlewarefunctionalityThispaperpresentstheContextObjectpatternthatallowsefficientprocessingofrequestsbypropagatingcontextinformationbetweendifferentmid-dlewarelayers.Usingthispattern,alayer/ses
4、sionpropa-gatesper-requestinformationrequiredbythenextlayer/sessioninacontextobject,whicheliminatestheneedfor(1)per-requeststatewithineachlayerand(2)lock-ing/synchronizationtoaccessper-requestinformationacrossdifferentlayers.ThispatternisusedinCORBAOb
5、jectRequestBrokers(ORBs)forrequestprocessing.1IntentThispatternprovidesanefficient,andapplication-transparentwayofsharinginformationbetweendifferentlayersinasoftwaresystem.Figure1.LayeredCORBARequestProcessingInourexample,asshowninFigure1(anddiscussed
6、in2ExampleAppendixA),requestprocessingsteps1-2arecarriedoutManyapplicationsusemiddlewaretoshieldthemfromintheI/Olayer,steps3-5arecarriedoutintheORBcoresystem-specificissues,suchascommunicationprotocols,layer,andstep6isexecutedintheobjectadapterlayer.I
7、nconcurrencystrategies,(de)multiplexingstrategies,oraddition,eachlayerrequiressomeinformationprocessed(de)marshalingmechanisms.Thistransparencyhelpsde-byalayerdirectlybeneathit.Forexample,thenameofthevelopersfocusonapplicationneeds,ratherthanwrestling
8、operationdemarshaledintheI/Olayerisrequiredinthewithlow-leveldistributiondetailsexplicitlyandmanually.objectadapterlayertoperformtheupcall.Similarly,aToprovidethedifferentmiddlewarefunctionalities,mid-messageparserassociatedintheORBcorelayeris
