[Mullender 85] - ontolinux.com

1 [Mullender85] ,VrijeUniversiteit,1985.[Ousterhout87]Jo hnOusterhout,AndrewCherenson,FredDouglis ,MichaelNelson, ;login:, , , {17,January/February1987.[Sun86] ,Inc., [Swinehart86] , , , , , ,October1986.[Watanabe88] ,LanguagesandApplicationsin1988,ACM,Sept ember1988.[Xerox81] , [Yokote87] ,LanguagesandApplicationsin1987,ACM,Octo ber1987.[Young87]MichaelYoung,AvadisTeva nian,RichardRashid,DavidGolub,Je reyEppinger,JonathanChew,WilliamBolosky, DavidBlack, ,DepartmentofComputerSci-ence,Carnegie-M ellonUniversity, ectedinthe [Anderson88] ,ComputerScienceDivision(EECS),Universit yofCalifornia,Berkeley,February1988.[Cam pbell87]RoyCampbell,VincentRusso, ++Conference,USENIXA ssocia-tion,November1987.[Cheriton86] ,ACM,August1986.}

2 [Cheriton88] , , , {333,March1988.[Cointe87] ,LanguagesandApplicationsin1987,ACM,Octo ber1987.[Dasgupta86] , ,LanguagesandApplicationsin1986,ACM,Sept ember{October1986.[Goldberg83] ,1983.[Jul88]EricJul,HenryLevy,NormanHut chinson, , , ,February1988.[Lieberman86] ,LanguagesandApplicationsin1986,ACM,Sept ember{October1986.[Maes87] ,VUBAI-LAB, ortconsistsof :ThebasicarchitectureofMuseisdesigned,su chasbasicabstractionofthesystem,storagea rchitecture,communicationmechanisms,prot ectionmechanisms, ,speci cationofseveralkernelfunctionalitiesareb eingdescribedinConcurrentSmall-talk[Yoko te87].6 CONCLUSIONT hispaperpresentedtheMuseobjectmodelwhich providesare : , (andthereforeatcompile-time).Thisfacilit atesdi erentialprogrammingandcodereuse.}}}

3 , , ,inheritancecontributestoe ,delegationisadynamicrelationshipwhichen ablesustobuilda exiblesystemarchitecture. Themodelprovidesare cientlyimplement nethepropertiesofstorageofanobject, , : gettingthestatusofapagetableentrytodecid ewhatpagesshouldbeswappedout, invalidatingthepagetableentriesofthecand idates, swappingoutthecandidatepagesusingthedisk driver, , rsttime,Skeletonisallocatedonthemeta-met a-objectlevel, , , ,themessagename:subclassOf: , , ,aftertheMuseworldhasbeenbuilt, , gurationspeci (2) (1).It ndsoutthattherequestisforanotherobjecton itself,anditsendstherequesttothecalledob ject.(3)Communicationbetweenobjectswhich runondi (1), ndsoutthattherequestisforanotherobjectwh ichexistsonanothermeta-object, (4)and(5) , ,therearesomemeta-objectsthatprovidenetw orkcommunicationfacilitieswhichcoverunde rthesessionlayerprotocolsuchasTCP/IPandV MTP[Cheriton86].

4 ,(4)and(5)showthecontrol owsofremotecommunication.(4)Communicatio nbetweenobjectswhichrunondi , ndsoutthattherequestisforanobjectwhichex istsonanothermeta-meta-object, (5)Communicationbetweenanobjectandameta- objectwhichrunondi , ndsoutthattherequestisforameta-objectwhi chexistsonanothermeta-meta-object, , ,whenanobjectwaitsforevents, ,streams,messagepassing, ,thecontrol gure,solidlinesindicateapathofcommunicat ion, (5)meta-metametaobject(1)meta-metametame taobjectobject(3)objectobjectmetametamet a-metameta-meta(4)objectobjectmetameta-m eta(2)meta-metameta-metametametaobjectFi gure5:ControlFlowsoftheMuseCommunication Systemindicateexecutionpathofprimitivein ter-objectcommunicationmethods,andthickd ottedlinesindicatepathofcommunicationexe cutedbymeta-objects.

5 (1) , : , Traphandling,suchashandlingofpagefaulttr aps, [Jul88], [Sun86]andCourier[Xerox81] ,aclassholdsthefollowinginformation:name :Nameoftheclassisspeci :Listofnamesofsuperclassesisspeci eldisusedasahintfordecidingwhichmeta-obj ectisresponsibleofcreatinganewobjectandd e ,fordeterminingtheformatofstoragearea, , :ifthetargethostisheterogeneousfromtheor iginalhost, :Hardwaredependentbinarycodes( ) , , ciencysake, ,methodsofsuperclassesarecollectedintoth eclassitself, , ,inheritanceispre-cededbydelegation,sinc ethenamesofmethodswhicharede , , ,adefaultpager,communicationprotocolshan dling,transactionprocessing, : MMUmanipulation,suchasreadingandwritingp agetableentries, Devicemanagementanddrivers,suchasactivat inganddeactivatingdevices,han-dlinghardw areinterrupts, nedinsuchawaythataphysicalprocessorexecu tesnativecodes( ) ectivearchitectureandattractiveinthehete rogeneousenvironment, ,computationcanbereducedtoexchangingmess agesbetweenobjectsandmutationofobjectsup onreceiptofrequests, , : , providehighspeedcommunication, ,weintroducethefollowingthreeprimitivein ter- , , ,theMuseoperatingsystemusesthethree-leve lstructure:objectlevel,meta-objectlevel, :manyprimitiveswhichareissuedbyobjectson thislevelarede.

6 TheSummaryoftheModel ,objectsinothersystemsarepassive, Objectsandtheirmeta-objectsarecausallyco nnected, uencecomputationofobjectsim-plicitly. Sinceobjectscanbeaccessedonlybytheserver process, tofthemeta-objectimplicitly. Ameta-objectcande ,thesemanticsofthesendoperationinobjects isde ectivearchitecture,themetahierarchy,thec lasssystem,schedulingofobjects,communica tion,storagemanagement, ectivearchitec- ectivearchitecture,anobjectisinterpreted bythemeta-objectandcomputationofthemeta- objectcanbein , ,\knowabout"meansanobjectknowsthenameofi tsmeta-objectbyavariabledenotingitandame ta-objectknowsthenameoftheobjectsbyobjec tdescriptors( ) ection,whilesendingamessagetoitsmeta-obj ect( )isanexampleofexplicitre ectedasfollows.

7 Sincethemeta-objectknowsthestatusoftheob jects,itcanchangeitsownbehaviortomanaget heobjectse ciently, Themeta-objectcanchangeameta-objectwhich hasotherfunctionstodelegaterequestsuponr eception,and , ,computationofanobjectcanbere ,sincethestatusofthemeta-objectcannotbek nowntoobjectsatanytimebecauseofprotectio nreasons, ,wegivea gure(Figure3) (oradaemon)inothersystemssuchasV-system, Mach, ,thefollowingsaredi :modi ,thenotionofaclassisintroducedforthefoll owingreasons: Thecodeofmethodsde nedintheclasscanbesharedbetweenobjects( )oftheclass. Aclasscanbeviewedasatemplatewhichisuseda sahintforcreatinganewobjectandconverting therepresentationofanobjecttobesuitablef orthetargethostuponmigration. Aclassisde nedasastaticandimmutableentity,sothatiti seasytomanageduplicationofaclassinthedis tributedenvironment.

8 Di neameta-objectasavirtualmachineandtode nedasasubclassofotherclasses, ,themeta-objectlevel, , , [Lieberman86] , , , :Point ClassTemplatename:#PointsubclassOf: :subclassOf:in:,ClassTemplatesendsreques twith:toMetaclasstocreateanewclasswhichi sde nedasasubclassofObject, ,classescorrespondtocookie-cutters,Class Templateisacookie-cutter-die, , :TheMetaHierarchyAmeta-objectisalsoanobj ect,sothatitisde nedbyanotherobject, , nitetowersarenotpracticalinthedesignofan operatingsystem,however,theMuseobjectmod elcollapsesthein , :anObject :selftothemeta-objectwhichcanbedetermine dbyusingthemeta: eldofitsclass(describedlater). : : Executionofamethodintheclassoftheobjecti sconceptuallyde nedbythemeta-object. Thesemanticsofcommunicationbetweenobject sisde nedbythemeta-object.

9 Themeta-objectisresponsibleforprovidinga nobjectwithlocalstoragehavingdesiredfunc tionality,forexample, , ,whenanobjectmigratestoanotherhost, , Howisthelocalstorageofanobjectmanaged?Wh oprovidesthestorageforanobjectwhilethere presentationisprovidedbythemeta-object? ,therearenode nitionsofthestoragewhichholdstheliststru cture. Howisacommunicationschemesuchasmessagepa ssing,remoteprocedurecalls,andstreamsdes cribed? ,the ,however, , , ,wede , ,are , ,whocancreateanddestroyanobject?Whocande necommunicationbetweenobjects?Whocanmana gethelocalstorageofanobject?Thatis,whoca nde necomputationofanobject? ,objectsarelocatedonthreelevels:objectle vel,meta-objectlevel, nedbyanotherobjectwhichisonthemeta-objec tlevel, , ,forexample,hasobsoletedataduetohardware crashandsimultaneousaccesstodata,usersca nnotobtaincorrectdata.

10 , :forexample, :forexample, ,thesystemshouldprovidesecureaccessingme thodstoobjects. ,applicationsmustobtainthedesiredinforma tioninspeci edtimeperiods. , , ,anobject, les, , ,however, ectivearchitecture[Maes87]whichhastwokin dsofobjects,objectsandmeta-objects, eldofprogramminglanguages,severalre ectiveobject-orientedprogramminglanguage shavebeeninvestigatedsuchas3-KRS[Maes87] ,ObjVlisp[Cointe87],andABCL/R[Watanabe88 ].Wefoundsomeproblemsintheselanguageswhe nwetriedtoapplytheirconceptstobuildingop eratingsystems, ,forexample,therearetwoabstractionsinthe system:a leisastatic, ,however, ,thesystemshouldbeself- ,however, [Swinehart86].But,tomeetvariouskindsofre quirementsfromprogrammers, (computationinULDS)isbeyondthescopeofthi spaperandwillbediscussedinthefuturepaper s,abriefdescriptionfollows.