-操作系统精髓与设计原理(第五版)+课后题答案1

CHAPTER2OPERATINGSYSTEMOVERVIEWReviewQuestions2.1Convenience:Anoperatingsystemmakesacomputermoreconvenienttouse.Efficiency:Anoperatingsystemallowsthecomputersystemresourcestobeusedinanefficientmanner.Abilitytoevolve:Anoperatingsystemshouldbeconstructedinsuchawayastopermittheeffectivedevelopment,testing,andintroductionofnewsystemfunctionswithoutinterferingwithservice.2.5Theexecutioncontext,orprocessstate,istheinternaldatabywhichtheoperatingsystemisabletosuperviseandcontroltheprocess.Thisinternalinformationisseparatedfromtheprocess,becausetheoperatingsystemhasinformationnotpermittedtotheprocess.Thecontextincludesalloftheinformationthattheoperatingsystemneedstomanagetheprocessandthattheprocessorneedstoexecutetheprocessproperly.Thecontextincludesthecontentsofthevariousprocessorregisters,suchastheprogramcounteranddataregisters.Italsoincludesinformationofusetotheoperatingsystem,suchasthepriorityoftheprocessandwhethertheprocessiswaitingforthecompletionofaparticularI/Oevent.Problems2.1Theanswersarethesamefor(a)and(b).Assumethatalthoughprocessoroperationscannotoverlap,I/Ooperationscan.1Job:TAT=NTProcessorutilization=50%2Jobs:TAT=NTProcessorutilization=100%4Jobs:TAT=(2N–1)NTProcessorutilization=100%2.4Asystemcallisusedbyanapplicationprogramtoinvokeafunctionprovidedbytheoperatingsystem.Typically,thesystemcallresultsintransfertoasystemprogramthatrunsinkernelmode.CHAPTER3PROCESSDESCRIPTIONANDCONTROLReviewQuestions3.5Swappinginvolvesmovingpartorallofaprocessfrommainmemorytodisk.WhennoneoftheprocessesinmainmemoryisintheReadystate,theoperatingsystemswapsoneoftheblockedprocessesoutontodiskintoasuspendqueue,sothatanotherprocessmaybebroughtintomainmemorytoexecute.3.10Theusermodehasrestrictionsontheinstructionsthatcanbeexecutedandthememoryareasthatcanbeaccessed.Thisistoprotecttheoperatingsystemfromdamageoralteration.Inkernelmode,theoperatingsystemdoesnothavetheserestrictions,sothatitcanperformitstasks.Problems3.1•Creationanddeletionofbothuserandsystemprocesses.Theprocessesinthesystemcanexecuteconcurrentlyforinformationsharing,computationspeedup,modularity,andconvenience.Concurrentexecutionrequiresamechanismforprocesscreationanddeletion.Therequiredresourcesaregiventotheprocesswhenitiscreated,orallocatedtoitwhileitisrunning.Whentheprocessterminates,theOSneedstoreclaimanyreusableresources.•Suspensionandresumptionofprocesses.Inprocessscheduling,theOSneedstochangetheprocess'sstatetowaitingorreadystatewhenitiswaitingforsomeresources.Whentherequiredresourcesareavailable,OSneedstochangeitsstatetorunningstatetoresumeitsexecution.•Provisionofmechanismforprocesssynchronization.Cooperatingprocessesmaysharedata.Concurrentaccesstoshareddatamayresultindatainconsistency.OShastoprovidemechanismsforprocessessynchronizationtoensuretheorderlyexecutionofcooperatingprocesses,sothatdataconsistencyismaintained.•Provisionofmechanismforprocesscommunication.TheprocessesexecutingundertheOSmaybeeitherindependentprocessesorcooperatingprocesses.Cooperatingprocessesmusthavethemeanstocommunicatewitheachother.•Provisionofmechanismsfordeadlockhandling.Inamultiprogrammingenvironment,severalprocessesmaycompeteforafinitenumberofresources.Ifadeadlockoccurs,allwaitingprocesseswillneverchangetheirwaitingstatetorunningstateagain,resourcesarewastedandjobswillneverbecompleted.3.3Figure9.3showstheresultforasingleblockedqueue.Thefigurereadilygeneralizestomultipleblockedqueues.CHAPTER4PROCESSDESCRIPTIONANDCONTROLReviewQuestions4.2Lessstateinformationisinvolved.4.5Addressspace,fileresources,executionprivilegesareexamples.4.61.Threadswitchingdoesnotrequirekernelmodeprivilegesbecauseallofthethreadmanagementdatastructuresarewithintheuseraddressspaceofasingleprocess.Therefore,theprocessdoesnotswitchtothekernelmodetodothreadmanagement.Thissavestheoverheadoftwomodeswitches(usertokernel;kernelbacktouser).2.Schedulingcanbeapplicationspecific.Oneapplicationmaybenefitmostfromasimpleround-robinschedulingalgorithm,whileanothermightbenefitfromapriority-basedschedulingalgorithm.TheschedulingalgorithmcanbetailoredtotheapplicationwithoutdisturbingtheunderlyingOSscheduler.3.ULTscanrunonanyoperatingsystem.NochangesarerequiredtotheunderlyingkerneltosupportULTs.Thethreadslibraryisasetofapplication-levelutilitiessharedbyallapplications.4.71.Inatypicaloperatingsystem,manysystemcallsareblocking.Thus,whenaULTexecutesasystemcall,notonlyisthatthreadblocked,butalsoallofthethreadswithintheprocessareblocked.2.InapureULTstrategy,amultithreadedapplicationcannottakeadvantageofmultiprocessing.Akernelassignsoneprocesstoonlyoneprocessoratatime.Therefore,onlyasinglethreadwithinaprocesscanexecuteatatime.Problems4.2Because,withULTs,thethreadstructureofaprocessisnotvisibletotheoperatingsystem,whichonlyschedulesonthebasisofprocesses.CHAPTER5CONCURRENCY:MUTUALEXCLUSIONANDSYNCHRONIZATIONReviewQuestions5.1Communicationamongprocesses,sharingofandcompetingforresources,synchronizationoftheactivitiesofmultipleprocesses,andallocationofprocessortimetoprocesses.5.9Abinarysemaphoremayonlytakeonthevalues0and1.Ageneralsemapho