d4.1 - allscale runtime system interface … - allscale runtime system...d4.1 – allscale runtime...

H2020 FETHPC-1-2014

AnExascaleProgramming,Multi-objectiveOptimisationandResilience

ManagementEnvironmentBasedonNestedRecursiveParallelismProjectNumber671603

D4.1–AllScaleruntimesysteminterfacespecification

WP4:UnifiedruntimesystemforextremescalesVersion: 1.0Author(s): ThomasHeller(FAU),ArneHendricks(FAU),HebertJordan(UIBK),PeterThoman(UIBK)Date: 28/03/16

Duedate: PM6Submissiondate: day/month/yearProjectstartdate: 01/10/2015Projectduration: 36monthsDeliverableleadorganization FAU

Version: 1.00Status Final

Author(s):

ThomasHeller(FAU)ArneHendricks(FAU)HerbertJordan(UIBK)PeterThoman(UIBK)

Reviewer(s) KirilDichev(QUB),ThomasFahringer(UIBK)

DisseminationlevelPU Public DisclaimerThis deliverable has been prepared by the responsible Work Package of theProjectinaccordancewiththeConsortiumAgreementandtheGrantAgreementNr671603.Itsolelyreflectstheopinionofthepartiestosuchagreementsonacollectivebasis in thecontextof theProjectand to theextent foreseen in suchagreements.

Acknowledgements

TheworkpresentedinthisdocumenthasbeenconductedinthecontextoftheEU Horizon 2020. AllScale is a 36-month project that started on October 1st,2015andisfundedbytheEuropeanCommission.

Thepartners in theprojectareUNIVERSITÄTINNSBRUCK(UBIK),FRIEDRICH-ALEXANDER-UNIVERSITÄT ERLANGEN NÜRNBERG (FAU), THE QUEEN'SUNIVERSITY OF BELFAST (QUB), KUNGLIGA TEKNISKA HÖGSKOLAN (KTH),NUMERICALMECHANICSAPPLICATIONS INTERNATIONALSA (NUMEXA), IBMIRELANDLIMITED(IBM).

The content of this document is the result of extensive discussionswithin theAllScaleConsortiumasawhole.

MoreinformationPublic AllScale reports and other information pertaining to the project are available through the AllScale public Web site under http://www.allscale.eu.VersionHistoryVersion Date Comments,Changes,Status Authors,

contributors,reviewers

0.1 21/02/16 Firstdraft ThomasHeller0.2 03/03/16 Seconddraft ArneHendricks0.3 07/03/16 Thirddraft ArneHendricks0.4. 16/03/16 Finaldraft ArneHendricks1.0 19/03/16 Finalversion ThomasHeller

Table of Contents1 Introduction...................................................................................................................................52 RuntimeInterface........................................................................................................................62.1Tuple-Spaces...........................................................................................................62.2AllScaleRuntimeInterface.................................................................................82.3KeyConceptsexplained.......................................................................................92.3.1DataItem..........................................................................................................................132.3.2WorkItem........................................................................................................................132.3.3Region-Realization....................................................................................................152.3.4Fragment-Realization..............................................................................................162.3.5DataItem-Realization..............................................................................................162.3.5WorkItem-Realization............................................................................................182.3.6Scheduler-Realization............................................................................................19

3 Monitoring/Events...................................................................................................................204 InterfacetothePerformanceandResilienceMonitor..............................................205 InterfacetotheResilienceManager.................................................................................216 ConclusionsandFutureWork.............................................................................................21

1 IntroductionTheruntimesysteminterfaceisthelayerdescribingthestructureofanapplicationthatcanbemanagedandtunedbytheAllScaleruntimesystem.ThefundamentalfunctionalityandpropertiesofthisessentialinterfacewillbedeterminedbyTaskT2.1andincorporatedintheoverallsystemarchitecturebyTaskT2.2.Simultaneously,toaidtheinterfacespecificationwithintaskT2.2,weformalizetheinvolvedentitiesthroughactualspecificationsthereofusingC++declarations.Theruntimeinterfaceisconnectedtothetoolsandentitiesdevelopedbytheotherworkpackages,suchasworkpackage5,andcanbeseeninthelowerdiagram,highlightedincyan.

Themaininteractingareasarewiththecompiler,theonlinemonitoringtoolandtheresiliencemanager.Duetothehighlevelofcouplingtoothercomponentsit

isveryimportantfortheresultingruntimeinterfacespecificationtofindamodelofexpressingparallel(recursive)tasks,datadependencies,IOcharacteristics,andhardwarerequirementsaswellasmeansforofferingmultiple,exchangeableimplementationsconstitutingdifferentvariationsofthesamecodefragmentandmeta-datacapturingresiliencepropertiesoftheprovidedcodes,inparticularfailurecompensationstrategies.

2 RuntimeInterfaceTheruntimeinterfaceisbasedonatheoreticalfoundationwithsimilaritiestothetuple-spaceparadigm.Thisparadigmdefinesacollectionoftuplestobeaccessedandusedconcurrently.ItwasintroducedbyDavidGelernteratUniversityofYaleinthe1980sbytheLindacoordination-language.ApplicationsusingLindaanditstuple-spacesrealizecommunicationamongprocessesbydefiningacollectionoftuples(Key-Valuepairs)andinformationisexchangedbywriting/loading(consuming/producing)tuples.Itwasanearlyapproachtoadistributedsharedmemory,andthekeyconceptsbeneathit,i.e.modelinganapplication’scommunicationintermsofproducingandconsumingsharedresources,issimilartomodernapproachessuchastheAllScaleruntimeinterface.

2.1Tuple-SpacesAtuple-spaceholdsanumberofKey-Valuepairs,whichcanbeconcurrentlymanipulated.Thecommunicationishandledbyapplyingreadandstoreoperationsonthesetuples,commonlyreferredtoasconsumeandproduceoperations.Thekeyconceptbehindit,i.e.dividinganapplication’stasksbymeansofproducingandconsumingsharedresources,isverysimilartomodernapproachessuchastheAllScaleruntime-interface.Atuple-spaceenvironmentoffersatleastthreeoperations:•Amethodtoinsertatupleintothespace,originallyreferredtoastheout()method•Amethodtowithdrawtuplesfromthetuple-space,thein()method•Amethodtoreadatuplefromthetuple-spacewithoutremovingit,theread()method.Thefollowingdiagramsdescribetheinteractionof4consumerswith2distincttuple-spaces,inserting,readinganddeletingtuples:

InsteadofpassingmessagesbetweentwoprocessesAandB,itisnowpossibleforthemtocommunicatebyaccessingthetuplespaces:processAcreatesoneormoretuplesencodingthemessagetobeconveyed,addsthemtothetuple-spacefromwhereprocessBmayconsumethembywithdrawingorreadingthem.Thebehaviorisdescribedinthefigurebelow:

Anumberofinterestingpropertiesoriginatefromthetuplespaceparadigm,rootedinitsprincipleofcommunicationorthogonality(neithersendernorreceiverhavepriorknowledgeabouteachother):anuncouplingofcommunicationbothinregardsoftimeandspace.Spaceuncouplingreferstotheconceptofdistributionofresources,allowing1:Ncommunicationaswellas1:1betweenprocesses.Timeuncoupling,ontheotherhand,meansthataproducingprocesscanruntocompletionandterminate,whileitsproducedtuplesremaininthetuple-spaceoncetheyareadded,availableforotherprocessestobeconsumed.Thisconcepthasremainedveryimportantovertheyears,andisalso

appliedbyHPXwithitsreferencecountingwithintheActiveGlobalAddressSpace(AGAS).Theproducersandconsumerscanbespreadacrossadistributedaddressspace-theyarestillabletoaccessthetuples,andatupleisusuallyuniqueinthetuple-space.Itshouldbeclearfromthediagramthatthemodelleadstoaformofshared,distributedmemoryspace,becausetuplescanactuallyresideondifferentphysicalnodesbutmaystillbeaccessedbytheothermembersThedetailsoftheseconceptscanbefoundin:LindainContext(1989).ThekindreadermightalsobeinterestedintheapproachoftheIntelConcurrentCollections,atemplatelibraryforC++parallelanddistributedapplications,introducingadataandcontrolflowmodeldistantlysimilartooursandinfluencedbytheconceptsoftuple-spaces.

2.2AllScaleRuntimeInterfaceWewillnowcontinuewithanintroductionandexplanationofthefundamentalconceptsandentitiesoftheAllScaleruntimeinterface.Ourtheoreticalfoundationofmanagingconcurrentlyusedresourcesisinfluencedbythetuple-spaceparadigm.Ourconceptwilladdtothisgeneralideawhatwecalldecomposabletuples.Decomposabletuplesarerepresentedbyahierarchicaltreeoffutures.Eachtaskthatisspawnedwithintheschedulerwillreturnsuchafuture.Eachfuturerepresentsthecompletionandreturnvalueofarecursivetask.Thefigurebelowshowssuchadependencytreeoffutures:

Thefinalresultmightdependuponthecompletionofatreeofotherresults,whichis,forinstance,thecasewhenrecursivelycalculatingFibonaccinumbers.ByrelyingonHPXastheunderlyingruntimeAPI,wecanconstructthesetreesoffuturesusingData-Flowcontroltechniquesandadditionallyexecuteapplicationswithoutthread-suspensionorwaiting.Thiswillallowtheruntimetobeasresourceefficientaspossibleandnotwasteanymemoryinthestacksegmentbyhavingagreatnumberofalreadyallocatedbutsuspendedthreads.Thelater

featurewillbeofgreatusewhendealingwithextremescaleconcurrencyleadingtobillionsofconcurrenttaskssuchastargetedbytheAllScaleenvironment.OurmainfoundationalentitiesarecalledWorkItemandDataItem.Instancesofthosetwocanbemodeledastuplesinatuple-space.Similartothetuplesinthediagramabove,ourentitiesneedtobeaccessedconcurrentlyandmightresidephysicallyspreadonaclusterofnodes.Theruntimeinterfaceoffersmethodsequivalenttoput()andget()inatuple-space,thewrite()orstore()aswellastheload()method,whichwillbedescribedinmoredetaillater.Differingtothetuple-spacepicturedabove,inourcaseitisalsopossibletoretrieveaTreeofFuturestotuples.Atreeoffuturesiscalled“Treeture”anditrepresentsthedependenciesamongnestedtaskstobecomputedbeforebeingabletoobtainthevaluepromisedbythetaskassociatedtotherootnode’sfuture.TheusageofTreeturescombinedwithoperationsonthefuturetree,suchasunionandintersect,enablesustohaveset-likebehaviorenhancingthetuple-space’sabilitiesbyaddingthepossibilityofretrievinga(partial)tuple,whichcorrespondstoa(sub-)treeoffutures.

2.3KeyConceptsexplainedWewillnowintroducesomeofthemainconceptsoftheruntimeinterfaceinaninformalway,withoutactualsourcecode.Furtherdowninthedocumentwewillshowsomeofthedetailsoftheplannedimplementationoftheruntimeinterfacetoprovideamoredetailedpictureoftheruntimetothereader.Toexplaintheconcepts,wewillrunthereaderthroughsomesimpleexamples,fromtoptobottom.Anapplication,e.g.asimplestencil,isruninparallelon4nodesofacluster.Thedataisstoredina1Darrayofvalues.Initiallytherecursivesplit-upoftasksisdonebytheAllScalecompiler;itprovidesimplementationsoftasksintheformofWorkItems.TheseWorkItemsareourentitiesthatdescribewhathastobedone(inourexampleperformingcomputationsonthestencilcells)andonwhichdata.Thedatacanbespreadoverthenetwork.Withinthestencilexample,therewillbetheneedtoaccessdatawhichresidedphysicallyonanothernodeinthecluster.Regardingthemanagementofdata,therearethreeconceptsthatneedfurtherexplanation:Regions,Fragments,andCollectionFacades.ARegionexposesinformationtoaddresssubsetsofelementswithinacollection.Inanarraylikecollection,regionsmightberealizedbydescribingsetsofindicesor,morecompact,asanintervalofindices.Fortreeshapeddatastructures,regionsmaybeaddressedbyaddressingrootnodesofsubtreestobeaddressed.TheactualdatastorageisrealizedbyFragments,whichcorrespondstotheobjectinstantiatedontheindividualnodes.Eachfragmentcontainsashareoftheoverallcollectionanddatamaybemovedbetweenfragmentinstances.Thedatawithinfragmentsistherebyaddressedbytheassociatedregionstructure.Thefollowingfigurevisualizestherelationbetweenregionsandfragmentsforour1Darrayexample:

ARegionisdefined,coveringindices4to7,andcanthenbeusedtocreateafragment,includingthedataaddressablebythoseindices.Dependingontheunderlyingdatastructure,regionsneedtoincludedifferentparameters:inthesimple1Dexamplethesearejuststartandendindices(columnindices),butfora2Darrayinformationabouttherowisneededaswell:

Asmentionedabove,theRegionconceptisversatile,andcanalsobeusedtoaccessstructureslikeatree:

InordertoprovideaunifiedAPItotheuser,hidingtheinternaldatamanagement,weintroduceCollectionFacades,whichareauser-facingwrapperstocreateandmanipulatedistributeddatacollections.ACollectionFacadeappearslikeitisaccessinggloballyshareddata,whileinfactitisaccessinglocalizedFragments,managedbytheruntimesystem.Thismakesmanagingthedatapossibleinadistributedenvironment.TheinteractionofFragmentsandCollectionFacadesinadistributedenvironmentisillustratedinthefigurebelow.

AswecoveredtheRegion,Fragment,andCollectionFacadeconcepts,wewillnowintroducetheDataItem.InordertocreateaDataItem,aDataItemDescriptioniscreated,whichbasicallyexposedtypeinformationassociatedtoaDataItem.Thusitsummarizeswhattypesareusedtoprocessthedata,includingthetypesforRegions,Fragments,andCollectionFacades.

2.3.1DataItemTheDataItemitselfisasymbolicrepresentationtosomemanageddataelement.Typicaluser-levelcodemightaccesselementsinanarrayjustbyusinganarray,becausethisapproachwillfailtosufficewhenworkinginadistributedsystem,thedataneedstobesomehowwrappedbyamanagement-layer.ThisiswhatDataItemsdo.EachDataItemhasauniquesymbolicname:aglobalidentifier.ItalsousesaRegioninstancetodescribethefullsizeofthe(virtual)dataitem.Itistheruntimesjobtotakethefullsizeofthedataitem,partitionitintosmallersub-regionsandcreatefragmentscoveringthosesub-regionsthroughouttheavailablenodes.Thisdatadistributionmaylaterbeadjusteddynamically,tofacilitateloadbalancing/managementoperationsortoreactonchangesintheinfrastructure,likejoiningorfailingnodes.

2.3.2WorkItemHavingexplainedDataItem,itistimetoillustratetheWorkItemconcept.AWorkItemistheruntimeinterfacetodescribeatask,withadditionaldatadependenciesandvariouscodevariants.

Itisconstructedbyutilizingatemplate,calledWorkItemDescription.ThistemplatecontainsinformationabouttheresultweexpectfromtheWorkItem,aswellasthetypeofdata/parametersthetaskneedstobeprocessed,called“Closure”type.Itcanalsocontainmultipleimplementationsoftheactualtask.Thisiscoveredbytuple<WorkItemVariants…>fieldinthedescription.WeneedtodefinethetermWorkItemVariantatleastroughly,becauseitisessentialforunderstandinghowWorkItemsareconstructed:AWorkItemVariantisatemplateclassthatisusedtodescribeoneimplementationofaworktask.

Itconsists,amongotherthings,ofarequiresfunctionwhichreturnsalistofdatadependenciesimposedbytheexecutionofthecorrespondingcodevariant.Thoserequirementslistsub-regionsofDataItemsandaccessmodes(e.g.ReadOnlyorReadWrite)whichwillhavetobeaccessibleonanynodesupposedtoprocessestheassociatedtask.TheWorkItemVariantalsocontainstheexecutemethod,whichistheactualimplementationofthecomputation.Thisiswheretheusercodewillbelocated.Thereturnvalueoftheexecutemethodiswhatwecalla“Treeture”.AtleastoneWorkItemVariantisneededtogenerateaWorkItemDescription,whichinturnisneededtogenerateanactualWorkItem.However,therecanbemultiplevariants,e.g.whenthecompilerissynthesizingspecializedcodeversionsforspecificusecase(sequentialexecution,checkpointcreation)ortargetarchitectures(variousaccelerators).Therearealsotwoentitiestoadministratetheseitems:theschedulerandamanagerforDataItemswhichwillbepresentedlater.Havingdiscussedthebasicelementsinaninformalandabstract,waywewillnowcontinuetodescribethesamecomponentsinregardsoftheiractualrepresentationintheinterface,i.e.writtencode.

2.3.3Region-RealizationAsexplained,aregioninstanceaddressesasubsetofelementsofacollection.Regionsareneededtoreferencesetsofelementsindataobjects.Theyhavetosupportasetofoperations.Oneveryimportantbeingtheloadoperation,whichloadsaRegionfromanarchiveobtainedfromthenetwork.OtheroperationsincludeunionandintersectionofRegionsofthesametype,needforthemanagementofdatapartitions.///Descriptiononhowthedataisaccessedenumaccess_privilige{read_only,write_first,read_write,write_only,accelerator_read_access,accelerator_write_access,accelerator_read_write_access,};template<typenameRegion>structis_region;///CalculatestheunionoftworegionsRegionmerge(Regionconst&region1,Regionconst&region2);///CalculatestheintersectionoftworegionsRegionintersection(Regionconst&region1,Regionconst&region2);///\returntrueiftheregionisempty,falseotherwiseboolempty(Regionsconst&region);///LoadsaRegionfromanarchivewhichhasbeenobtainedfromthenetworktemplate<typenameArchive,typenameRegion>voidload(Archive&archive,Region&region);///SavesaRegiontoanarchivewhichissupposedtobesentoverthe

///networktemplate<typenameArchive,typenameRegion>voidsave(Archive&archive,Region&region);

2.3.4Fragment-RealizationAFragmentisastorageforasub-setofelementsofacollection,whichisaddressedbyaRegion: ///AFragmentisareferenceintoacollectionofdatawithaspecific ///viewpointexpressedwithaRegion Fragmentcreate(Regionconst&region); voidresize(Fragmentconst&fragment,Regionconst&region); OutFragmentmask(Fragmentconst&fragment,Regionconst&region);

voidinsert(Fragment&destination,Fragmentconst&source,Regionconst&region);

voidsave(Archive&ar,Fragmentconst&fragment); voidload(Archive&ar,Fragment&fragment);

2.3.5DataItem-RealizationThestatictypepartofadata_itemcannowbedescribedusingatemplateparameterDataItemDescription,whichisusedtocreateit.ADataItemDescriptioncontainsinformationaboutthetypesusedtoprocessthedataitem:///ConceptCollectionFacade:///ACollectionFacadeistheuserfacingtypewhichislogicallyrepresenting///aglobalviewonthedata,however,itmightonlyhaveaccesstoaacquired///fragmentwhichisjustasubset///Informationaboutthetypesusedtoprocessadataitemtemplate<typenameRegion,typenameFragment,typenameCollectionFacade>classdata_item_description{usingregion_type=Region;usingfragment_type=Fragment;usingcollection_facade=CollectionFacade;};WhereCollectionFacadeistheinterfacetotheend-user,aglobalviewtothedistributeddatacollection.Thedata_itemitselfcontainsthefullsizeofthedataitemintheformofaregion_typevalue,andauniqueidentifiertoidentifythedata_itemglobally:///Asymbolicrepresentationtosomemanageddataelement(collection)template<typenameDataItemDescription>classdata_item{usingregion_type=typenameDataItemDescription::region_type;///Createsadataitemwithauniqueidentifierdata_item();///Returnstheuniqueidentifiertoadataitemid_typeget_id()const;};

Creation,acquisitionanddeletionofdata_itemsistheresponsibilityofthedata_item_manager,whichoffersacreate,destroy,acquire,andreleasemethodandistheinterfacetothecompiler:classdata_item_manager{///createsasymbolicinstanceforadataitemtemplate<typenameExecutor,typenameDataItemDescription>data_item<DataItemDescription>create(typenameDataItemDescription::region_typeconst&size,Executor=this_executor);///destroyasymbolicinstanceforadataitemtemplate<typenameDataItemDescription>voiddestroy(data_item<DataItemDescription>item);///Calledinthegeneratedcode(fromthecompiler)///whenthedataisaccessedtemplate<typenameDataItemDescription>typenameDataItemDescription::collection_typeacquire(requirement<DataItemDescription>const&requirement);///Calledinthegeneratedcode(fromthecompiler)///whenthedataisnotneededanymoretemplate<typenameDataItemDescription>voidrelease(requirement<DataItemDescription>const&requirement);///\returnsthelocationsofwherethefragmentstodataitems///thatthepassedregionscontainsarelocatedtemplate<typenameDataItemDescription>future<std::vector<std::pair<typenameDataItemDescription::region_type,locality>>>locate(requirement<DataItemDescription>const&requirement);///\paramshopping_listalistofrequirementswithalocalityhint///indicatingonwhatshouldbegathered//////\returnThisfunctionreturnsafuturethatbecomesreadywhenthe///datahasbeensuccesfullycopiedtothesystemtemplate<typenameExecutor,typenameDataItemDescription>future<void>gather(Executorconst&executor,std::vector<std::pair<requirement<DataItemDescription>,locality>>const&shopping_list);};data_itemsareinterfacedwiththework_itemsbytheWorkItemVariant,agenericconceptthatfeaturesarequires(Closureconst&closure)method,whichreturnsalistofrequirements.Arequirementreferencesadata_item,thesub-regionoftheitemtobeaccessed,andaccessprivilegesneededfortheassociatedtasktobeprocessed.template<typenameResult>classWorkItemVariant{///\returnIftheworkitemvariantwasgenerated;constexprboolvalid;

///\tparamClosureListofcapturedvariablesthatistheused///dataitemsandpassedparameters///\returnAlistofrequirementstemplate<typenameClosure>staticunspecifiedrequires(Closureconst&closure);///Executesthegivenvariantusingthecapturedvariablesintheclosure///onceallrequirementshavebeenfullfilledtemplate<typenameClosure>statictreeture<Result>execute(Closureconst&closure);template<typenameClosure,typenameNonFunctionalProperty>statictypenameNonFunctionalProperty::result_typenon_functional_property(Closureconst&closure);};

2.3.5WorkItem-RealizationTheWorkItemVariantexposesanexecutemethodwhichispassedaClosureasparameter(representingthecapturedvariablesintheClosureonceallrequirementshavebeenacquiredbytheuseofthedata_item_manager),andthenexecutesthegivenvariant.WorkItemVariantalsooffersthepossibilitytospecifyadditionalnon-functional-propertiescharacterizingtherepresentedcodevariant.Thesecanincludethingssuchasparallelgranularity,resiliencyrequirements,andmemoryusagepatternsaswellaswhetherornotGPUsorotheracceleratorsareutilizedforthecomputation.Thisinformationismadeavailabletotheschedulerforconductingschedulingdecisions.WorkItemVariantsareusedtocreateWorkItemDescriptions:template<typenameResult,typenameClosure,typenameSplitVariant,typenameProcessVariant,typename...WorkItemVariant>classwork_item_description{usingresult_type=Result;usingclosure_type=Closure;usingsplit_variant=SplitVariant;usingprocess_variant=ProcessVariant;usingwork_items=std::tuple<WorkItemVariant...>;};EachWorkItemDescriptioncancontainanumberofWorkItemVariants,representedbyastd::tuple<WorkItemVariant...>.Inordertocreateawork_itemobject,aWorkItemDescriptionispassedastemplateparametertothework_itemclass,resultinginawork_itemfeaturingthegivenWorkItemDescription.classwork_item_base;template<typenameWorkItemDescription>classwork_item:work_item_base{usingresult_type=typenameWorkItemDescription::result_typeusingclosure_type=typenameWorkItemDescription::closure_type;

work_item(closure_type&&closure);};Anothermethodneededfortheschedulingistherunmethod:///Executeagivenvariantwiththeclosure,thisgetscalledfromwithin///theschedulertemplate<typenameExecutor,typenameWorkItemVariant,typenameClosure>voidrun(Executor,Closure&&closure);ItispassedaWorkItemVariantandanassociatedclosureinordertoexecutethegivenvariantonahardwareresourcedeterminedbyfirstparameterbeinganHPXexecutorinstance.

2.3.6Scheduler-RealizationHavingintroducedthebasicclassesneededfordependency,dataandworkdescriptions,wewillnowintroducetheschedulerinterface.Theschedulerisagenericcomponentintheglobaladdressspace,whichisresponsibletomakedecisionsregardingwhereandhowtoprocessworkitems,wheretoplacesub-regionsofdataitems,andhowtotunehardwareparameters.Itfeaturesaspawnmethod,whichisresponsibleforschedulingtheexecutionofagivenWorkItem,byfirstselectingoneofitscodevariantsandalocationforitsexecution,followedbyforwardingtheselectedoptionstotherunmethodoutlinedabove. structscheduler{///Flushesthequeuesandabortsalltasksthathaven'tbeenstartedyetvoidflush();///Thisfunctionwillbegeneratedinthecompilerandeventually///spawnsaspecificWorkItemVariantbasedonsomeschedulerdecisiontemplate<typenameWorkItemDescription>treeture<typenameWorkItemDescription::result_type>spawn(typenameWorkItemDescription::closure_typeconst&closure);private:};Thespawnmethodisinvokedbythecodegeneratedbythecompiler,withagenericparameterWorkItemDescription,describingthework_itemitwillbecreating.Asvisiblefromthesignatureabove,spawnwillbegivenaparameterWorkItemDescription::closure_typeconst&closure.Itisusedtocapturethefunctions“callingcontext”,includingcapturedparametersanddataitems.ThespawnmethodreturnsaTreetureprovidingafuturehandletotheresultsoftheworkitem.TypeinformationaboutthetypeoftheresultintheFuture-TreeareprovidedbytheWorkItemDescription::result_typetemplateparameterofthetreeturereturntypeofthespawnmethod.

2.4HardwareTheconfigurationofthehardwareisaccessiblethroughtopologyinformation,thatis,localtopologyoftheunderlyingprocessor/nodewithrespecttoprocessingunits,memoryandinterconnects.///Returnsatopologyofexecutorsthatcover:///-NUMADomains///-Symmetricmultiprocessing///-Accelerators///-Providesdifferentsetsofcorestouse///-Differentlowlevelschedulingpolicies:///*FIFOordering///*Workstealingwithinthesetofcores///*...executor_topologyget_topology();Sincetheschedulermightneedtobeabletomakedecisionsinvolvingmorethanoneprocess/localityitshouldmakeuseoftheHPXcommunicationfacilitiesbyregisteringschedulerswithauniquenameandresolvethenamestoGlobalIDsinordertomakecallschedulerdefinedactionstomakefurtherdecisions.

3 Monitoring/EventsTheruntimesystemexposesanAPIbasedonHPXperformancecounterswhichallowsthefollowing:

• GenerateAllScaleSpecificPerformanceCounterData• Globallydiscoverableandqueryable• Subscribable:eventonchangeoreventonchangegivenaspecific

thresholdetc.ThiswillformthebasisforthePerfomanceMonitorandResilienceManagercomponentsastheywillbeabletoa)registercountersandb)reactonthecounterstoeithergeneratenewworkitemsorgenerateeventsfortheschedulertoreacton.

4 InterfacetothePerformanceandResilienceMonitorWorkPackage5isthetaskofdevelopinglanguageandtoolsupportforcontinuousmonitoringofapplicationperformanceanderrorresilience,aswellassupportforapplication-specific,algorithmicerrordetectionandrecoveryfrombotherrorsandperformanceanomaliesduetonon-deterministicvariabilityinperformance.Inordertoaccomplishthistasktheruntimeneedstobeinterfacedtothecross-layerresiliencemonitor.TheinterfacetothetooldevelopedinWP5willbebasedonHPXperformancecounters.Itcanthusprovidearangeofinformation,includinglocality-specificperformancemetricssuchasthreadqueuelength,statesofthreadsandworkitems,andcachestatistics.Thisinformationcanthenbeusedbytheperformancemonitortoinformthedynamicoptimizertomakeprudentdecisionsatruntime.

5 InterfacetotheResilienceManagerInordertoprovideresiliencesupport,theruntimesystemwillprovidefunctionalitytobackup/restoredataitemsandworkitemstates.Intheeventofanetworkornodefailure,oranyotherdisruption,theresiliencemanagerwillorchestratearecoveryprocess.Ithastobediscussedwhichcomponentisdetectingnetworkfaults.Furthermore,globalcheckpointingneedstobeavoidedduetoitsdetrimentaleffectonperformance.

6 ConclusionsandFutureWorkOurspecificationallowsustoexpresstasks,datadependencies,andnon-functionalrequirementssuchashardwarerequirementsinaparallel-readyway.Theusageoftemplate-heavycodeassuresmaximumflexibilityforfurtherdevelopmentaswellasperformancebenefits.Paradigmssuchastheworkanddataitemshavetheadvantageofofferingwaystoutilizemultipleimplementationsofvariationsofthesamecodefragments.TheperformanceMonitorandresiliencemanagerinterfacesarestillveryearlyintheirplanningphaseandneedstobefurtherrefinedbasedontheinsightsobtainedoverthecourseofthedevelopmentprocess.BibliographyD. Gelernter - Linda in Context (1989).

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