操作系统精髓与设计原理第五版 课后题答案.docx

操作系统精髓与设计原理第五版 课后题答案.docx

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操作系统精髓与设计原理第五版课后题答案

Chapter2

OperatingSystemOverview

ReviewQuestions

2.1Convenience:

Anoperatingsystemmakesacomputermoreconvenienttouse.Efficiency:

Anoperatingsystemallowsthecomputersystemresourcestobeusedinanefficientmanner.Abilitytoevolve:

Anoperatingsystemshouldbeconstructedinsuchawayastopermittheeffectivedevelopment,testing,andintroductionofnewsystemfunctionswithoutinterferingwithservice.

2.5Theexecutioncontext,orprocessstate,istheinternaldatabywhichtheoperatingsystemisabletosuperviseandcontroltheprocess.Thisinternalinformationisseparatedfromtheprocess,becausetheoperatingsystemhasinformationnotpermittedtotheprocess.Thecontextincludesalloftheinformationthattheoperatingsystemneedstomanagetheprocessandthattheprocessorneedstoexecutetheprocessproperly.Thecontextincludesthecontentsofthevariousprocessorregisters,suchastheprogramcounteranddataregisters.Italsoincludesinformationofusetotheoperatingsystem,suchasthepriorityoftheprocessandwhethertheprocessiswaitingforthecompletionofaparticularI/Oevent.

Problems

2.1Theanswersarethesamefor（a）and（b）.Assumethatalthoughprocessoroperationscannotoverlap,I/Ooperationscan.

1Job:

TAT=NTProcessorutilization=50%

2Jobs:

TAT=NTProcessorutilization=100%

4Jobs:

TAT=（2N–1）NTProcessorutilization=100%

2.4Asystemcallisusedbyanapplicationprogramtoinvokeafunctionprovidedbytheoperatingsystem.Typically,thesystemcallresultsintransfertoasystemprogramthatrunsinkernelmode.

Chapter3

ProcessDescriptionandControl

ReviewQuestions

3.5Swappinginvolvesmovingpartorallofaprocessfrommainmemorytodisk.WhennoneoftheprocessesinmainmemoryisintheReadystate,theoperatingsystemswapsoneoftheblockedprocessesoutontodiskintoasuspendqueue,sothatanotherprocessmaybebroughtintomainmemorytoexecute.

3.10Theusermodehasrestrictionsontheinstructionsthatcanbeexecutedandthememoryareasthatcanbeaccessed.Thisistoprotecttheoperatingsystemfromdamageoralteration.Inkernelmode,theoperatingsystemdoesnothavetheserestrictions,sothatitcanperformitstasks.

Problems

3.1•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.

Chapter4

ProcessDescriptionandControl

ReviewQuestions

4.2Lessstateinformationisinvolved.

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.

Problems

4.2Because,withULTs,thethreadstructureofaprocessisnotvisibletotheoperatingsystem,whichonlyschedulesonthebasisofprocesses.

Chapter5

Concurrency:

MutualExclusionandSynchronization

ReviewQuestions

5.1Communicationamongprocesses,sharingofandcompetingforresources,synchronizationoftheactivitiesofmultipleprocesses,andallocationofprocessortimetoprocesses.

5.9Abinarysemaphoremayonlytakeonthevalues0and1.Ageneralsemaphoremaytakeonanyintegervalue.

Problems

5.2ABCDE;ABDCE;ABDEC;ADBCE;ADBEC;ADEBC;

DEABC;DAEBC;DABEC;DABCE

5.5Considerthecaseinwhichturnequals0andP

（1）setsblocked[1]totrueandthenfindsblocked[0]settofalse.P（0）willthensetblocked[0]totrue,findturn=0,andenteritscriticalsection.P

（1）willthenassign1toturnandwillalsoenteritscriticalsection.

Chapter6

Concurrency:

DeadlockandStarvation

ReviewQuestions

6.2Mutualexclusion.Onlyoneprocessmayusearesourceatatime.Holdandwait.Aprocessmayholdallocatedresourceswhileawaitingassignmentofothers.Nopreemption.Noresourcecanbeforciblyremovedfromaprocessholdingit.

6.3Theabovethreeconditions,plus:

Circularwait.Aclosedchainofprocessesexists,suchthateachprocessholdsatleastoneresourceneededbythenextprocessinthechain.

Problems

6.4a.0000

0750

6622

2002

0320

b.tod.Runningthebanker'salgorithm,weseeprocessescanfinishintheorderp1,p4,p5,p2,p3.

e.Changeavailableto（2,0,0,0）andp3'srowof"stillneeds"to（6,5,2,2）.Nowp1,p4,p5canfinish,butwithavailablenow（4,6,9,8）neitherp2norp3's"stillneeds"canbesatisfied.Soitisnotsafetograntp3'srequest.

6.51.W=（2100）

2.MarkP3;W=（2100）+（0120）=（2220）

3.MarkP2;W=（2220）+（2001）=（4221）

4.MarkP1;nodeadlockdetected

Chapter7

MemoryManagement

ReviewQuestions

7.1Relocation,protection,sharing,logicalorganization,physicalorganization.

7.7Alogicaladdressisareferencetoamemorylocationindependentofthecurrentassignmentofdatatomemory;atranslationmustbemadetoaphysicaladdressbeforethememoryaccesscanbeachieved.Arelativeaddressisaparticularexampleoflogicaladdress,inwhichtheaddressisexpressedasalocationrelativetosomeknownpoint,usuallythebeginningoftheprogram.Aphysicaladdress,orabsoluteaddress,isanactuallocationinmainmemory.

Problems

7.6a.The40Mblockfitsintothesecondhole,withastartingaddressof80M.The20Mblockfitsintothefirsthole,withastartingaddressof20M.The10Mblockisplacedatlocation120M.

b.Thethreestartingaddressesare230M,20M,and160M,forthe40M,20M,and10Mblocks,respectively.

c.Thethreestartingaddressesare80M,120M,and160M,forthe40M,20M,and10Mblocks,respectively.

7.12a.Thenumberofbytesinthelogicaladdressspaceis（216pages）´（210bytes/page）=226bytes.Therefore,26bitsarerequiredforthelogicaladdress.

b.Aframeisthesamesizeasapage,210bytes.

c.Thenumberofframesinmainmemoryis（232bytesofmainmemory）/（210bytes/frame）=222frames.So22bitsisneededtospecifytheframe.

d.Thereisoneentryforeachpageinthelogicaladdressspace.Thereforethereare216entries.

e.Inadditiontothevalid/invalidbit,22bitsareneededtospecifytheframelocationinmainmemory,foratotalof23bits.

d.Thethreestartingaddressesare80M,230M,and360M,forthe40M,20M,and10Mblocks,respectively.

Chapter8

VirtualMemory

ReviewQuestions

8.1Simplepaging:

allthepagesofaprocessmustbeinmainmemoryforprocesstorun,unlessoverlaysareused.Virtualmemorypaging:

notallpagesofaprocessneedbeinmainmemoryframesfortheprocesstorun.;pagesmaybereadinasneeded

8.2Aphenomenoninvirtualmemoryschemes,inwhichtheprocessorspendsmostofitstimeswappingpiecesratherthanexecutinginstructions.

Problems

8.1a.Splitbinaryaddressintovirtualpagenumberandoffset;useVPNasindexintopagetable;extractpageframenumber;concatenateoffsettogetphysicalmemoryaddress

b.（i）1052=1024+28mapstoVPN1inPFN7,（7⨯1024+28=7196）

（ii）2221=2⨯1024+173mapstoVPN2,pagefault

（iii）5499=5⨯1024+379mapstoVPN5inPFN0