操作系统并发性互斥和同步ppt课件.ppt

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1、Concurrency:MutualExclusionandSynchronizationChapter51ConcurrencyOverviewThecentralthemesofoperatingsystemdesignareallconcernedwiththemanagementofprocessesandthreads:MultiprogrammingMultiprocessingDistributedprocessingFundamentaltooperatingsystemdesignisconcurrency(并发)TheBasicrequirementfo

2、rsupportofconcurrencyistheabilitytoenforcemutualexclusion(互斥)2ConcurrencyContexts(并发上下文)Concurrencyarisesinthreedifferentcontexts:MultipleapplicationsMultiprogrammingStructuredapplicationApplicationcanbeasetofconcurrentprocessesorthreadsOperating-systemstructureOperatingsystemisasetofproce

3、ssesorthreads3DesignIssuesofConcurrencyCommunicationamongprocessesSharingandcompeting(竞争)ofresourcesSynchronizationoftheactivitiesofmultipleprocessesAllocationofprocessortimetoprocesses4PrinciplesofConcurrencyInterleavingOverlappingBasiccharacteristicofmultiprogrammingsystems:relativespeed

4、ofexecutionofprocessescannotbepredicted5DifficultiesofConcurrencySharingofglobalresourcesForexample:GlobalvariableOperatingsystemmanagingtheallocationofresourcesoptimallyForexample:I/OchannelDifficulttolocateprogrammingerrorsProgramresultsarenotdeterministicandreproducible(再现)6ASimpleExamp

5、levoidecho(){chin=getchar();chout=chin;putchar(chout);}ProcessP1ProcessP2..chin=getchar();..chin=getchar();chout=chin;chout=chin;putchar(chout);..putchar(chout);..7RaceCondition(竞争条件)Whenmultipleprocessesorthreadsaccesssharedresourcesothatthefinalresultdependsontheorderofexecutionofinstruc

6、tionsinthemultipleprocessesMurphyLawIfSomethingcangowrong,itwill.SolutiontoRaceCondition:ControlaccesstothesharedresourceMutualExclusion(互斥)8ProcessInteractionThreepossibledegreesofawarenessamongprocesses:ProcessesunawareofeachotherCompetitionProcessesindirectlyawareofeachotherCooperationP

7、rocessdirectlyawareofeachotherCooperation9CompetitionAmongProcessesforResourcesCriticalsections(临界区)PortionoftheprogramthataccesssharedresourceOnlyoneprogramatatimeisallowedinitscriticalsectionExampleonlyoneprocessatatimeisallowedtosendcommandtotheprinterEnfor