ThreadManagement(join)

Joinblocksthecallingthreaduntilthetargetthreadterminates,andreturnsit’sthread_exit argument.Itisimpossible tojoinathreadinadetachedstate.Itisalsoimpossibletoreattachit

intpthread_join (pthread_t thread,void**value_ptr)[OUT]threadreturnvalue

int pthread_detach (pthread_t thread)int pthread_attr_setdetachstate (pthread_attr_t *attr, [IN/OUT]attribute

int detachstate)[IN]statetobesetint pthread_attr_getdetachstate (const pthread_attr_t *attr,

int *detachstate)[OUT]detachstatevalue

ThreadManagement(state)

ThePOSIXstandarddoesnotdictatethesizeofathread'sstack!

int pthread_attr_getstacksize (const pthread_attr_t *restrictattr,size_t *restrictstacksize)

int pthread_attr_setstacksize (pthread_attr_t *attr,size_t stacksize)int pthread_attr_getstackaddr (const pthread_attr_t *restrictattr,

void**restrictstackaddr)int pthread_attr_setstackaddr (pthread_attr_t *attr,void*stackaddr)pthread_t pthread_self (void)int pthread_equal (pthread_t t1,pthread_t t2)

Example:AProducer– ConsumerQueue

• Wehaveaboundedqueuewhereproducersstoretheiroutputandfromwhereconsumerstaketheirinput

• Protectthestructureagainstintensiveunnecessaryaccesses– Detectboundaryconditions:queueemptyandqueuefull

Boun

dedQue

ue

…producers

…consumers

Example:dot-product

• Dividethearraysbetweenparticipantstoload-balancethework– Eachwillthencomputeapartialsum

• Addallthepartialsumstogetherforthefinalresult(reduceoperation)

• Technicaldetails:costofmanagingthethreadsvs.costofthealgorithm?Howtominimizethemanagementcost?

Scalarproduct,innerproduct

=PN

n=1 ai.bi

a

b

a

b

Thr 1 Thr 2 Thr 3

Partialsum

Partialsum

Partialsum

+

+

Homework:thediningphilosophersproblem

Dijkstra,1965:Fivesilentphilosopherssitataroundtablewithbowlsofspaghetti.Forksareplacedbetweeneachpairofadjacentphilosophers.Eachphilosophermustalternatelythinkandeat.However,aphilosophercanonlyeatspaghettiwhenhehasbothleftandrightforks.Eachforkcanbeheldbyonlyonephilosopherandsoaphilosophercanusetheforkonlyifitisnotbeingusedbyanotherphilosopher.Afterhefinisheseating,heneedstoputdownbothforkssotheybecomeavailabletoothers.Aphilosophercantaketheforkonhisrightortheoneonhisleftastheybecomeavailable,butcannotstarteatingbeforegettingbothofthem.Eatingisnotlimitedbytheremainingamountsofspaghettiorstomachspace;aninfinitesupplyandaninfinitedemandareassumed.

2

15

4

3

Deliverin2weeks(Friday09/09):Apdf documentwiththedescriptionoftheproblemasyouunderstanditandwiththesolutionyouchoosetoimplement.Implementasolutionforanunboundednumberofphilosophers,whereeachphilosopherisimplementedasathread,andtheforksarethesynchronizationsneededbetweenthem.ProvidetheCsourcecodeandamakefile,allowingforsmoothcompilationandexecution.