进程管理英文课件

Chapter4:ProcessesProcessConceptProcessSchedulingOperationonProcessesCooperatingProcessesInterprocessCommunicationProcessConceptAnoperatingsystemexecutesavarietyofprograms:Batchsystem–jobsTime-sharedsystems–userprogramsortasksTextbookusesthetermsjobandprocessalmostinterchangeably.Process–

aprograminexecutionAprocessincludes:programcounterstackdatasectionProcessConcept国内学术界较为一致的定义：

进程是一个具有一定独立功能的程序，关于某个数据集合的一次可以并发执行的运行活动。FromWikipedia

Incomputing,aprocessisaninstanceofacomputerprogramthatisbeingsequentiallyexecutedbyacomputersystemthathastheabilitytorunseveralcomputerprogramsconcurrently.Processvs.ProgramDynamic/staticprocessisaprograminexecution,soitisdynamic,programisapassivecollectionofinstuctions,soitisastaticentity.Lifycycleprocesshasalifecycle.Itisanactiveentityinthesensethatitcanbecreated,executed,andterminatedduringitslifetime.Programcanexistforever.Structureprocess=program+data+PCBEachprocessisrepresentedintheOSbyaprocesscontrolblock(PCB),itcontainsallinformationassociatedwithaspecificprocess.Processvs.ProgramNoone-to-onemappingbetweenprocessesandprogramscanhavemulitpleprocessesofthesameprogramoneprocesscaninvokemultipleprogramsProcessisthebasicunitofbeingscheduledandresourceallocationfromtheviewpointofOS,whileprogramcannotberunwithoutprocesscreation.Processcanbeexecutedconcurrentlyorsimultaneously.ProcessStateAsaprocessexecutes,itchangesstatenew:Theprocessisbeingcreated.running:Instructionsarebeingexecuted.waiting:Theprocessiswaitingforsomeeventtooccur.ready:Theprocessiswaitingtobeassignedtoaprocessor.terminated:Theprocesshasfinishedexecution.ProcessControlBlock(PCB)Informationassociatedwitheachprocess：Processstate Programcounter CPUregisters CPUschedulinginformation Memory-managementinformationAccountinginformation I/OstatusinformationProcessControlBlock(PCB)CPUSwitch

FromProcesstoProcessProcessSchedulingProcessSchedulingQueuesJobqueue

–setofallprocessesinthesystem.Readyqueue

–setofallprocessesresidinginmainmemory,

readyandwaitingtoexecute.Devicequeues

–setofprocesseswaitingforanI/Odevice.Processmigrationbetweenthevariousqueues.ReadyQueueAnd

VariousI/ODeviceQueuesRepresentation

ofProcessSchedulingAdditionof

MediumTermSchedulingSchedulers(Cont.)Short-termschedulerisinvokedveryfrequently(milliseconds)Þ(mustbefast).调用频率高Long-termschedulerisinvokedveryinfrequently(seconds,minutes)Þ(maybeslow).调用频率不高Thelong-termschedulercontrolsthedegreeofmultiprogramming.

长程调度控制了多道程序的“道数”Processescanbedescribedaseither:I/O-boundprocess

–spendsmoretimedoingI/Othancomputations,manyshortCPUbursts.CPU-boundprocess

–spendsmoretimedoingcomputations;fewverylongCPUbursts.ContextSwitch上下文切换WhenCPUswitchestoanotherprocess,thesystemmustsavethestateoftheoldprocessandloadthesavedstateforthenewprocess.Context-switchtimeisoverhead;thesystemdoesnousefulworkwhileswitching.Timedependentonhardwaresupport.ProcessCreation(Cont.)AddressspaceChildduplicateofparent.Childhasaprogramloadedintoit.UNIXexamplesforksystemcallcreatesnewprocessexeclpsystemcallusedafteraforktoreplacetheprocess’memoryspacewithanewprogram.

ATreeofProcesses

OnATypicalUNIXSystemProcessTerminationProcessexecuteslaststatementandaskstheoperatingsystemtodeleteit(exit).Process’resourcesaredeallocatedbyoperatingsystem.Outputdatafromchildtoparent(viawait).ParentmayterminateexecutionofchildrenprocessesChildhasexceeded超过allocatedresources.Taskassignedtochildisnolongerrequired.Parentisexiting.Operatingsystemdoesnotallowchildtocontinueifitsparentterminates.Cascadingtermination.级联终止Producer-ConsumerProblemParadigmforcooperatingprocesses,producerprocessproducesinformationthatisconsumedbyaconsumerprocess.unbounded-bufferplacesnopracticallimitonthesizeofthebuffer.

无界缓冲没有对缓冲区大小的限制bounded-bufferassumesthatthereisafixedbuffersize.

有界缓冲对缓冲区大小作了限定Bounded-Buffer

——Shared-MemorySolutionShareddatavar

n;type

item=…;var

buffer.array[0..n–1]of

item;in,out:0..n–1;Producerprocess

repeatproduceaniteminnextp…while

in+1mod

n=out

do

no-op;buffer[in]:=nextp;in:=in+1mod

n;until

false;Threads(Cont.)Inamultiplethreadedtask,whileoneserverthreadisblockedandwaiting,asecondthreadinthesametaskcanrun.Cooperationofmultiplethreadsinsamejobconfershigherthroughputandimprovedperformance.Applicationsthatrequiresharingacommonbuffer(i.e.,producer-consumer)benefitfromthreadutilization.Threadsprovideamechanismthatallowssequentialprocessestomakeblockingsystemcallswhilealsoachievingparallelism.Kernel-supportedthreads(MachandOS/2).User-levelthreads;supportedabovethekernel,viaasetoflibrarycallsattheuserlevel.Hybridapproachimplementsbothuser-levelandkernel-supportedthreads(Solaris2).混合处理实现用户级和内核支持线程InterprocessCommunication-IPCMechanismforprocessestocommunicateandtosynchronizetheiractions.Messagesystem

–processescommunicatewitheachotherwithoutresortingtosharedvariables.IPCfacilityprovidestwooperationssend(message)–messagesizefixedorvariablereceive(message)IfPandQwishtocommunicate,theyneedto:establishacommunication

linkbetweenthemexchangemessagesviasend/receiveImplementationofcommunicationlinkphysical(e.g.,sharedmemory,hardwarebus)logical(e.g.,logicalproperties)ImplementationQuestionsHowarelinksestablished?Canalinkbeassociatedwithmorethantwoprocesses?Howmanylinkscantherebebetweeneverypairofcommunicatingprocesses?Whatisthecapacityofalink?？Isthesizeofamessagethatthelinkcanaccommodatefixedorvariable?Isalinkunidirectionalorbi-directional?DirectCommunicationProcessesmustnameeachotherexplicitly显式:send(P,message)–sendamessagetoprocessPreceive(Q,message)–receiveamessagefromprocessQPropertiesofcommunicationlinkLinksareestablishedautomatically.Alinkisassociatedwithexactlyonepairofcommunicatingprocesses.Betweeneachpairthereexistsexactlyonelink.Thelinkmaybeunidirectional,butisusuallybi-directional.IndirectCommunicationMessagesaredirectedandreceivedfrommailboxes.Eachmailboxhasauniqueid.Processescancommunicateonlyiftheyshareamailbox.

PropertiesofcommunicationlinkLinkestablishedonlyifprocessesshareacommonmailboxAlinkmaybeassociatedwithmanyprocesses.Eachpairofprocessesmayshareseveralcommunicationlinks.Linkmaybeunidirectional.alorbi-directional.OperationscreateanewmailboxsendandreceivemessagesthroughmailboxdestroyamailboxTypesofMailboxPrivateMailbox:owner-Receiveotheruser-SendPublicMailbox:ownedbyOSSh