Message Passing Interface.ppt

municationtakesplaceviatheexplicitexchangeofdataormessages(realizedviasystemcallslikesend(...)orreceive(...)andothers),:targetID,messageinformation(type,length,...)body:thedatatobeprovidedNeedforabuffermechanism:whattodoifthereceiverisnot(yet)readytoreceive?TheUser’municationSystem(MPI)ProcessorProcessProcessProcessProcessorProcessProcessProcessProcessorProcessProcessorProcessDataexchangeMessageBuffersTypically(butnotnecessarily)connectedpartsofmemoryhomogeneousarchitectures(allprocessorsofthesametype):bufferasasequenceofbytes,withoutanytypeinformationheterogeneousarchitectures(differenttypesofprocessors):typeinformationnecessaryforformatconversionbymessagepassinglibraryDefinitionandallocationofmessagebuffers:sendbuffer:generallydonebyapplicationprogramreceivebuffer:eitherautomaticallybymessagepassinglibraryormanuallybyapplicationprogram(eventuallywithcheckwhetherbufferlengthissufficient)Point-to-municationApoint-to-–requiredinformation:receiver(whoshallgetthemessage?)sendbuffer(whereisthedataprovided?)typeofmessage(whatkindofinformationissent?)communicationcontext(contextwithinwhichthemessagemaybesentandreceived)Receive–requiredinformation:sender(wildcardsarepossible,)receivebuffer(ingmessagetobeput?)municationcontextPoint-to-municationContextConsiderascenario:threeprocesses,andallofthemcallasubroutinefromalibraryinter-parecorrectorder(nextslide)municationContextSubroutineSend(Proc0)Recv(Proc2)Process0Process1Process2SubroutineRecv(Proc1)Send(Proc2)SubroutineRecv(Proc0)Send(Proc1)Recv(any)Send(Proc0)municationContextConsiderascenario:threeprocesses,andallofthemcallasubroutinefromalibraryinter-parecorrectorder(previousslide)anderrorcase(nextslide)