lecture_7_Synchronization

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1、SynchronizationZhaoFangOperatingSystems-forthecollegestudentsGoalsforTodayWhyConcurrency?Whyisthebackgroundofsynchronization?MoreonCriticalSectionNeedforsynchronizationExamplesofvalidsynchronizationWhyConcurrency?AllowsmultipleapplicationstorunatthesametimeMultipleapplicationsStruc

2、turesapplicationsOperatingsystemstructureAnalogy:jugglingBenefitsofConcurrencyAbilitytorunmultipleapplicationsatthesametimeBetterresourceutilizationBetteraverageresponsetimeBetterperformanceDrawbacksofConcurrencyApplicationsneedtobeprotectedfromoneanotherAdditionalcoordinationmecha

3、nismsamongapplicationsOverheadtoswitchamongapplicationsPotentialperformancedegradationwhenrunningtoomanyapplicationsMotivatingExample:TooMuchMilkTworobotsareprogrammedtomaintainthemilkinventoryatastore…Theyarenotawareofeachother’spresence…Robot:DumbRobot:DumberMotivatingExample:TooMuch

4、MilkDumbDumber4:00Lookintofridge:OutofmilkMotivatingExample:TooMuchMilkDumbDumber4:00Lookintofridge:Outofmilk4:05HeadforthewarehouseMotivatingExample:TooMuchMilkDumbDumber4:05Headforthewarehouse4:10Lookintofridge:OutofmilkMotivatingExample:TooMuchMilkDumbDumber4:10Lookintofridge:Outofmilk4

5、:15HeadforthewarehouseMotivatingExample:TooMuchMilkDumbDumber4:15Headforthewarehouse4:20ArrivewithmilkMotivatingExample:TooMuchMilkDumbDumber4:15Headforthewarehouse4:20ArrivewithmilkMotivatingExample:TooMuchMilkDumbDumber4:20Arrivewithmilk4:25GopartyMotivatingExample:TooMuchMilkDumbDumber4

6、:20Arrivewithmilk4:25Goparty4:30Arrivewithmilk:“Uhoh…”DefinitionsSynchronization:useatomicoperationstoensurecooperationamongthreadsMutualexclusion:ensureonethreadcandosomethingwithouttheinterferenceofotherthreadsCriticalsection:apieceofcodethatonlyonethreadcanexecuteatatimeMoreDefinitio

7、nsAlockpreventsathreadfromdoingsomethingForexample:fixthemilkproblembyputtingakeyontherefrigeratorCorrectnessPropertiesNeedtobecarefulaboutcorrectnessofconcurrentprograms,sincenon-deterministicWhatarethecorrectnesspropertiesforthe“Toomuchmilk”problem???Ne