分布式系统设计.10

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1、DistributedSystemsPrinciplesandParadigmsMaartenvanSteenVUAmsterdam,Dept.ComputerScienceRoomR4.20,steen@cs.vu.nlChapter10:DistributedObject-BasedSystemsVersion:December2,2009ContentsChapter01:Introduction02:Architectures03:Processes04:Communication05:Naming06:Synchronization07:Consisten

2、cy&Replication08:FaultTolerance09:Security10:DistributedObject-BasedSystems11:DistributedFileSystems12:DistributedWeb-BasedSystems13:DistributedCoordination-BasedSystems2/40DistributedObject-BasedSystems10.1ArchitectureRemotedistributedobjectsDataandoperationsencapsulatedinanobjectOper

3、ationsimplementedasmethodsgroupedintointerfacesObjectoffersonlyitsinterfacetoclientsObjectserverisresponsibleforacollectionofobjectsClientstub(proxy)implementsinterfaceServerskeletonhandles(un)marshalingandobjectinvocationClientmachineServermachineObjectClientServerStateSameinterfaceMe

4、thodClientasobjectinvokesamethodSkeletonInterfaceinvokesProxySkeletonsamemethodatobjectClientOSServerOSNetworkMarshalledinvocationispassedacrossnetwork3/40DistributedObject-BasedSystems10.1ArchitectureRemotedistributedobjectsTypesofobjectsICompile-timeobjects:Language-levelobjects,from

5、whichproxyandskeletonsareautomaticallygenerated.Runtimeobjects:Canbeimplementedinanylanguage,butrequireuseofanobjectadapterthatmakestheimplementationappearasanobject.TypesofobjectsIITransientobjects:liveonlybyvirtueofaserver:iftheserverexits,sowilltheobject.Persistentobjects:liveindepe

6、ndentlyfromaserver:ifaserverexits,theobject’sstateandcoderemain(passively)ondisk.4/40DistributedObject-BasedSystems10.1ArchitectureExample:EnterpriseJavaBeans(EJB)WhatisitJavaobjecthostedbyspecialserverthatallowsfordifferentmeansofcallingtheobjectbyremoteclients.ContainerEJBEJBEJBServe

7、rJMSJNDIJDBCRMIServicesServerkernelLocalOSNetwork5/40DistributedObject-BasedSystems10.1ArchitectureTypesofEJBsFourdifferenttypesStatelesssessionbean:Transientobject,calledonce,doesitsworkandisdone.Example:executeanSQLqueryandreturnresulttocaller.Statefulsessionbean:Transientobject,bu