virtual processors and threads

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1、Module7VirtualProcessorsandThreadsVirtualProcessorsandThreads11-20037-1©2001,2003InternationalBusinessMachinesCorporationObjectivesAttheendofthismodule,youwillbeableto:®Defineathread®Describethemultithreadedarchitecture®DescribehowthevirtualprocessorsareimplementedinUNIX®UseonstattomonitorVPsa

2、ndthreads®Listandexplainthevirtualprocessorclasses®Describehownetworkconnectionsarehandledbytheserver®SetserverconfigurationparametersrelatedtoVPsandthreads®Dynamicallyaddandremovevirtualprocessors7-27-2VirtualProcessorsandThreadsWhatisaThread?AthreadisasequenceofinstructionsexecutedinaAthread

3、isasequenceofinstructionsexecutedinaprogram.program.CPUoninit7-3Beforelookingatserverarchitecture,itishelpfultofirstexaminethegeneralconceptofathread.Athreadcanbethoughtofasasequenceofinstructionsbeingexecutedinaprogram.Whenmultiplethreadsarerunwithinthesameentity(inourcaseanentityisaprocess),

4、itiscalledmultithreading.Athreadissometimesreferredtoasalightweightprocessinsomeliteraturebecauseitmakesfewerdemandsontheoperatingsystem.Inthefollowingpages,multithreadingisexplainedbycomparingtherelationshipbetweenathreadandaprocesstotherelationshipbetweenaprocessandanoperatingsystem.VirtualP

5、rocessorsandThreads7-3SingleThreadedVs.MultithreadedprocessprocessprocessThreeprocesses,singlethreadsOneprocess,multiplethreadsprocess7-4AregularUNIXprocessthatdoesnotimplementthreadscanbethoughtofasasingle-threadedprocess,althoughwedonotnormallycallitthat.Onesequenceofinstructionsisbeingexecu

6、tedforthisprocess,andtheoperatingsystemisresponsibleforschedulingandrunningtheprocess.Multithreadingisamethodofexecutingmanyiterationsofaprocessfordifferentuserswithouthavingtoformmanyinstancesofthatprocessattheoperating-systemlevel.AmultithreadedprocesscanhavemultiplethreadsrunningwithinaUNIX

7、process,eachrunningsequentiallyandgivingupcontroltootherthreadsataspecificpointintime.Howthisisaccomplishedmakesmultithreadingdifferentfromsimplyreceivingandexecutingrequestsfromasingleuser’sprocess.Multithreadingisasystemslevelconceptw