The Native POSIX Thread Library for Linux

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1、TheNativePOSIXThreadLibraryforLinuxUlrichDrepperIngoMolnarRedHat,Inc.RedHat,Inc.drepper@redhat.commingo@redhat.comFebruary21,2005Thisdocumentiscompletely,utterlyoutofdatewhenitcomestodescriptionsofthelimitationsofthecurrentimplementation.EverybodyreferringtothisdocumenttodocumentshortcomingsofNPTLis

2、eitheramoronwhohasn’tdoneher/hishomeworkandresearchedtheissue,orisdeliberatelymisleadingpeopleasithappenstoooftenwithpublicationsdonebytheEvilfromtheNorth-West.Today’sdemandsforthreadscanhardlybesatisfiedbytheLinux-ThreadslibraryimplementingPOSIXthreadswhichiscurrentlypartofthestandardruntimeenvironm

3、entofaLinuxsystem.Itwasnotwrittenwiththekernelextensionswehavenowandinthenearfutureavailable,itdoesnotscale,anditdoesnottakemodernprocessorarchitecturesintoaccount.Acompletelynewdesignisnecessaryandthispaperwilloutlinethedesignwecameupwith.1TheFirstImplementationTheLinuxThreadsimplementationwhichtod

4、ayisLinux’sstandardPOSIXthreadli-braryisbasedontheprinciplesoutlinedbythekerneldevelopersatthetimethecodeDraftwaswritten(1996).Thebasicassumptionisthatcontextswitchesamongrelatedpro-cesesarefastenoughtohandleeachuser-levelthreadbyonekernelthread.Kernelprocessescanhavevariousdegreesofrelationship.The

5、POSIXthreadspecificationrequiressharingofalmostallresources.Missingthread-awareABIsforthetargetarchitectures,thedesigndidnotusethreadregisters.Thethread-localmemorywasinsteadlocatedusingfixedrelation-shipsbetweenthestackpointerandthepositionofthethreaddescriptor.Inaddition,amanagerthreadhadtobecreated

6、tobeabletoimplementthecorrectsemanticswithrespecttosignals,threadcreation,andvariousotherpartsofprocessmanagement.Perhapsthebiggestproblemwastheabsenceofusablesynchronizationprimitivesinthekernelwhichforcedtheimplementationtoresorttousingsignals.This,togetherwiththeconceptofkernelthreadgroupsmissing

7、inthekernelversionsofthetime,leadtonon-compliantandfragilesignalhandlinginthethreadlibrary.2ImprovementsOverTimeThecodeofthethreadlibrarywassignificantlyimprovedoverthefollowingsixyears.Theimprovements