操作系统精髓与设计原理课件.ppt

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1、Concurrency:DeadlockandStarvationChapter6Outline6.1PrincipleofDeadlock6.2Deadlockprevention(死锁预防)6.3Deadlockavoidance(死锁避免)6.4Deadlockdetection(死锁检测)6.1PrincipleofdeadlockDefinition:PermanentblockingofasetofprocessesthateithercompeteforsystemresourcesorcommunicatewitheachotherNoefficientsol

2、utionInvolveconflictingneedsforresourcesbytwoormoreprocesses1、ReusableResourcesUsedbyoneprocessatatimeandnotdepleted(消耗掉)bythatuseProcessesobtainresourcesthattheylaterreleaseforreusebyotherprocessesProcessors,I/Ochannels,mainandsecondarymemory,files,databases,andsemaphoresDeadlockoccursifea

3、chprocessholdsoneresourceandrequeststheotherExampleofDeadlock,D&TAnotherExampleofDeadlockSpaceisavailableforallocationof200Kbytes,andthefollowingsequenceofeventsoccurDeadlockoccursifbothprocessesprogresstotheirsecondrequestP1......Request80Kbytes;Request60Kbytes;P2......Request70Kbytes;Requ

4、est80Kbytes;2、ConsumableResourcesCreated(produced)anddestroyed(consumed)byaprocessInterrupts,signals,messages,andinformationinI/ObuffersDeadlockmayoccurifaReceivemessageisblockingMaytakeararecombinationofeventstocausedeadlockExampleofDeadlockDeadlockoccursifreceiveisblockingP1......Receive(

5、P2);Send(P2,M1);P2......Receive(P1);Send(P1,M2);3、ResourceAllocationGraphsDirectedgraphthatdepictsastateofthesystemofresourcesandprocessesResourceAllocationGraphs4、ConditionsforDeadlockMutualexclusion(互斥—排它性访问资源)onlyoneprocessmayusearesourceatatimeHold-and-wait(占有且等待—拥有部分资源,还要请求新的)Aprocessd

6、oesnotrequestallofitsrequiredresourcesatonetimeConditionsforDeadlockNopreemption(非剥夺性—排他性访问资源)Ifaprocessholdingcertainresourcesisdeniedafurtherrequest,thatprocessmustnotreleaseitsoriginalresourcesIfaprocessrequestsaresourcethatiscurrentlyheldbyanotherprocess,theoperatingsystemisnotallowedto

7、preemptthesecondprocessandrequireittoreleaseitsresourcesConditionsforDeadlockCircularwait(循环等待—在进程资源图中有环路)PossibilityofDeadlockMutualExclusionNopreemptionHoldandwaitExistenceofDeadlockMutualExclusionNopreemptionHoldandwaitCircularwaitNecessarycondition6.