operatingsystem《操作系统》ch

Chapter3:Processes,ChapterObjectives,Tointroducethenotionofaprocess-aprograminexecution,whichformsthebasisofallcomputation.Todescribethevariousfeaturesofprocesses,includingscheduling,creationandtermination,andcommunication.Todescribecommunicationinclient-serversystems.,ContentOverview,ProcessConceptProcessSchedulingOperationsonProcessesCooperatingProcessesInterprocessCommunicationCommunicationinClient-ServerSystems,3.1ProcessConcept,Anoperatingsystemexecutesavarietyofprograms:BatchsystemjobsTime-sharedsystemsuserprogramsortasksTextbookusesthetermsjobandprocessalmostinterchangeablyProcessaprograminexecution;processexecutionmustprogressinsequentialfashionAprocessincludes:programcounterStackheapdatasectiontextsection,ProcessinMemory,ProcessState,Asaprocessexecutes,itchangesstatenew:Theprocessisbeingcreatedready:Theprocessiswaitingtobeassignedtoaprocessorrunning:Instructionsarebeingexecutedwaiting:Theprocessiswaitingforsomeeventtooccurterminated:Theprocesshasfinishedexecution,DiagramofProcessState,ProcessControlBlock(PCB),InformationassociatedwitheachprocessProcessstateProgramcounterCPUregistersCPUschedulinginformationMemory-managementinformationAccountinginformationI/Ostatusinformation,ProcessControlBlock(PCB),CPUSwitchFromProcesstoProcess,3.2ProcessScheduling,Theobjectiveofmultiprogrammingistohavesomeprocessrunningatalltimes,tomaximizeCPUutilization.TheobjectiveoftimesharingistoswitchtheCPUamongprocessessofrequentlythatuserscaninteractwitheachprogramwhileitisrunning.Tomeettheseobjectives,theprocessschedulerselectsanavailableprocess(possiblyfromasetofseveralavailableprocesses)forprogramexecutionontheCPU.Forasingle-processorsystem,therewillneverbemorethanonerunningprocess.Iftherearemoreprocesses,therestwillhavetowaituntiltheCPUisfreeandcanberescheduled.,ProcessSchedulingQueues,JobqueuesetofallprocessesinthesystemReadyqueuesetofallprocessesresidinginmainmemory,readyandwaitingtoexecuteDevicequeuessetofprocesseswaitingforanI/OdeviceProcessesmigrateamongthevariousqueues,ReadyQueueAndVariousI/ODeviceQueues,RepresentationofProcessScheduling,Schedulers,Long-termscheduler(orjobscheduler)selectswhichprocessesshouldbebroughtintothereadyqueueShort-termscheduler(orCPUscheduler)selectswhichprocessshouldbeexecutednextandallocatesCPU,AdditionofMediumTermScheduling,Schedulers(Cont.),Short-termschedulerisinvokedveryfrequently(milliseconds)(mustbefast)Long-termschedulerisinvokedveryinfrequently(seconds,minutes)(maybeslow)Thelong-termschedulercontrolsthedegreeofmultiprogrammingProcessescanbedescribedaseither:I/O-boundprocessspendsmoretimedoingI/Othancomputations,manyshortCPUburstsCPU-boundprocessspendsmoretimedoingcomputations;fewverylongCPUbursts,ContextSwitch,WhenCPUswitchestoanotherprocess,thesystemmustsavethestateoftheoldprocessandloadthesavedstateforthenewprocessContext-switchtimeisoverhead;thesystemdoesnousefulworkwhileswitchingTimedependentonhardwaresupport,3.3OperationsonProcesses,ProcessCreationParentprocesscreatechildrenprocesses,which,inturncreateotherprocesses,formingatreeofprocessesResourcesharingParentandchildrenshareallresourcesChildrensharesubsetofparentsresourcesParentandchildsharenoresourcesExecutionParentandchildrenexecuteconcurrentlyParentwaitsuntilchildrenterminate,ProcessCreation(Cont.),AddressspaceChildduplicateofparentChildhasaprogramloadedintoitUNIXexamplesforksystemcallcreatesnewprocessexecsystemcallusedafteraforktoreplacetheprocessmemoryspacewithanewprogram,ProcessCreation,CProgramForkingSeparateProcess,intmain()pid_tpid;pid=fork();/*forkanotherprocess*/if(pid0)/*erroroccurred*/fprintf(stderr,ForkFailed);exit(-1);elseif(pid=0)/*childprocess*/execlp(/bin/ls,ls,NULL);else/*parentprocess*/wait(NULL);/*parentwillwaitforthechildtocomplete*/printf(ChildComplete);exit(0);,AtreeofprocessesonatypicalSolaris,ProcessTermination,Processexecuteslaststatementandaskstheoperatingsystemtodeleteit(exit)Outputdatafromchildtoparent(viawait)ProcessresourcesaredeallocatedbyoperatingsystemParentmayterminateexecutionofchildrenprocesses(abort)for:ChildhasexceededallocatedresourcesTaskassignedtochildisnolongerrequiredIfparentisexitingSomeoperatingsystemdonotallowchildtocontinueifitsparentterminatesAllchildrenterminated-cascadingtermination,3.4InterProcessCommunication,IndependentprocesscannotaffectorbeaffectedbytheexecutionofanotherprocessCooperatingprocesscanaffectorbeaffectedbytheexecutionofanotherprocessAdvantagesofprocesscooperationInformationsharingComputationspeed-upModularityConvenienceCooperatingprocessesrequireanInterprocesscommunication(IPC)mechanismsharedmemory/messagepassing,CommunicationsModels,MessagePassingSharedMemory,Shared-MemorySolutionProducer-ConsumerProblem,Paradigmforcooperatingprocesses,producerprocessproducesinformationthatisconsumedbyaconsumerprocessunbounded-bufferplacesnopracticallimitonthesizeofthebufferbounded-bufferassumesthatthereisafixedbuffersize,Bounded-Buffer,Shareddata#defineBUFFER_SIZE10typedefstruct.item;itembufferBUFFER_SIZE;intin=0;intout=0;Solutioniscorrect,butcanonlyuseBUFFER_SIZE-1elements,Bounded-BufferInsert()Method,while(true)/*Produceanitem*/while(in=(in+1)%BUFFERSIZEcount)=out);/*donothing-nofreebuffers*/bufferin=item;in=(in+1)%BUFFERSIZE;,BoundedBufferRemove()Method,while(true)while(in=out);/donothing-nothingtoconsume/removeanitemfromthebufferitem=bufferout;out=(out+1)%BUFFERSIZE;returnitem;,Message-PassingSystems,MessagesystemprocessescommunicatewitheachotherwithoutresortingtosharedvariablesIPCfacilityprovidestwooperations:send(message)messagesizefixedorvariablereceive(message)IfPandQwishtocommunicate,theyneedto:establishacommunicationlinkbetweenthemexchangemessagesviasend/receiveImplementationofcommunicationlinkphysical(e.g.,sharedmemory,hardwarebus)logical(e.g.,logicalproperties)DirectorindirectcommunicationSynchronousorasynchronouscommunicationAutomaticorexplicitbuffering,*ImplementationQuestions,Howarelinksestablished?Canalinkbeassociatedwithmorethantwoprocesses?Howmanylinkscantherebebetweeneverypairofcommunicatingprocesses?Whatisthecapacityofalink?Isthesizeofamessagethatthelinkcanaccommodatefixedorvariable?Isalinkunidirectionalorbi-directional?,DirectCommunication-Naming,Processesmustnameeachotherexplicitly:send(P,message)sendamessagetoprocessPreceive(Q,message)receiveamessagefromprocessQPropertiesofcommunicationlinkLinksareestablishedautomaticallyAlinkisassociatedwithexactlyonepairofcommunicatingprocessesBetweeneachpairthereexistsexactlyonelinkThelinkmaybeunidirectional,butisusuallybi-directional,IndirectCommunication-mailbox,Messagesaredirectedandreceivedfrommailboxes(alsoreferredtoasports)EachmailboxhasauniqueidProcessescancommunicateonlyiftheyshareamailboxPropertiesofcommunicationlinkLinkestablishedonlyifprocessesshareacommonmailboxAlinkmaybeassociatedwithmanyprocessesEachpairofprocessesmayshareseveralcommunicationlinksLinkmaybeunidirectionalorbi-directional,IndirectCommunication,OperationscreateanewmailboxsendandreceivemessagesthroughmailboxdestroyamailboxPrimitivesaredefinedas:send(A,message)sendamessagetomailboxAreceive(A,message)receiveamessagefrommailboxA,IndirectCommunication,MailboxsharingP1,P2,andP3sharemailboxAP1,sends;P2andP3receiveWhogetsthemessage?SolutionsAllowalinktobeassociatedwithatmosttwoprocessesAllowonlyoneprocessatatimetoexecuteareceiveoperationAllowthesystemtoselectarbitrarilythereceiver.Senderisnotifiedwhothereceiverwas.,Synchronization,Messagepassingmaybeeitherblockingornon-blockingBlockingisconsideredsynchronousBlockingsendhasthesenderblockuntilthemessageisreceivedBlockingreceivehasthereceiverblockuntilamessageisavailableNon-blockingisconsideredasynchronousNon-blockingsendhasthesendersendthemessageandcontinueNon-blockingreceivehasthereceiverreceiveavalidmessageornull,Buffering,Queueofmessagesattachedtothelink;implementedinoneofthreeways1.Zerocapacity0messagesSendermustwaitforreceiver2.BoundedcapacityfinitelengthofnmessagesSendermustwaitiflinkfull3.UnboundedcapacityinfinitelengthSenderneverwaits,*3.5ExamplesofI