lecture_6_Cooperating Threads

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1、CooperatingThreadsZhaoFangOperatingSystems-forthecollegestudentsGoalsforTodayWhyallowcooperatingthreads?WhatareAtomicOperations?BackgroundProcessescanexecuteconcurrentlyMaybeinterruptedatanytime,partiallycompletingexecutionConcurrentaccesstoshareddatamayresultindatainconsi

2、stencyMaintainingdataconsistencyrequiresmechanismstoensuretheorderlyexecutionofcooperatingprocessesIndependentThreadsNostatessharedwithotherthreadsDeterministiccomputationOutputdependsoninputReproducibleOutputdoesnotdependontheorderandtimingofotherthreadsSchedulingorderd

3、oesnotmattere.g.,compilersCooperatingThreadsSharedstatesNondeterministicNon-reproduciblee.g.,elevatorcontrollersExample:2threadssharingthesamedisplayThreadAThreadBcout<<“ABC”;cout<<“123”;Youmayget“A12BC3”So,WhyAllowCooperatingThreads?Sharedresourcese.g.,asingleprocesso

4、rSpeedupOccurswhenthreadsusedifferentresourcesatdifferenttimesModularityAnapplicationcanbedecomposedintothreadsHigh-levelExample:WebServerServermusthandlemanyrequestsNon-cooperatingversion:serverLoop(){con=AcceptCon();ProcessFork(ServiceWebPage(),con);}Whataresomedisadva

5、ntagesofthistechnique?ThreadedWebServerNow,useasingleprocessMultithreaded(cooperating)version:serverLoop(){connection=AcceptCon();ThreadFork(ServiceWebPage(),connection);}ThreadPoolsProblemwithpreviousversion:UnboundedThreadsWhenweb-sitebecomestoopopular–throughputsinksIns

6、tead,allocateabounded“pool”ofworkerthreads,representingthemaximumlevelofmultiprogrammingqueueMasterThreadThreadPoolContinue……worker(queue){while(TRUE){con=Dequeue(queue);if(con==null)sleepOn(queue);elseServiceWebPage(con);}master(){}allocThreads(worker,queue);while(TRUE){con=Ac

7、ceptCon();Enqueue(queue,con);wakeUp(queue);}}SomeConcurrentProgramsIfthreadsworkonseparatedata,schedulingdoesnotmatterThreadAThreadBx=1;y=2;SomeConcurrentProgramsIfthreadssharedata,thefinalvaluesarenotasobviousThreadAThreadBx=1;y=2;x=y+1;y=y*2;Whataretheindivisibleoperations

8、?AtomicOperationsAnatomicoperationalwaysrunstocomplet