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Title

ソフトウェアの構成に関する研究

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on Loosely Coupled Distributed Systems

Masumi Toyoshima

Schoolof Information Science,

Japan Advanced Institute of Science and Technology

June 2001

Abstract

Thisthesis presentsatask allocationmethod to implementfault tolerant software using functionalpro-

grammingparadigm. Thedesignand implementation usinggroupcommunicationsystemisalso discussed

in ordertobuildtheruntimesystemonlooselycoupleddistributed environment.

Recently,manyCOTScomputersareconnectedusingLANorWANandthereariseseveralprojectswhich

usethecomputationpoweroftheseinexpensivecomputationresources.Intheselooselycoupleddistributed

environment,thereexistsmanycomponentsbuildupsinglesystem,there aredierentclassofperformance

of computers, and the communication links may be sometimes down. In order to run large applications

including longrunningscientic computation onsuch environment,it is important forsuch systemstobe

fault tolerance,thecharacteristicsofasystemtotoleratesomefaultand continuerunninginanacceptable

level.

Manyresearchworkhasbeendoneinthis areasince1970sandthere existssomebasictechniquestoim-

plementfaulttolerance. However,mostofthesetechniquesarebasedonimperativeprogrammingparadigm.

Thoughitiseasytounderstanditsoperationalsemanticsusingimperativeprogrammingparadigm,program-

mers have to consider many complication: detecting the fault, checkpointingsystem state and recovering

usingthem tocorrectstates,etc.

InordertoavoidthesediÆculties,APRreplicationtechniquewhich isbasedonfunctional programming

paradigmisintroducedin1998. Theholedevelopment,fromthemodelofcomputationthroughimplemen-

tationis introducedin APRapproach. APRprovidesnotonlyfaulttolerancebut italsoshortensthetime

to completecomputation. Itis onlyneededforprogrammerstodescribeapplication programin functional

mannerin ordertogaintheabovebenets.

Thoughtheschedulingalgorithm offunctions in APR isintroduced, theresourceallocationmethodnor

details ofdesign and implementation includingcommunicationin looselycoupled distributed environment

arestill notdened.

This theses starts with the formalization of APR task scheduling algorithm. Then the RAFT resource

management system is introduced in order to manage computation resources and allocate tasks to the

resources. RAFT divides APR functions to more ne-grainedtasks called RAFT process and distributes

these processesto thecomputation resourcesexisting on network. Therecovery process in RAFT is also

dened soastominimizetherecoverytimewhenfailuresoccur.

Thedesignandimplementationusinggroupcommunicationisalsointroducedinthisthesiswithitscost

analysis. Theseworksshowtheeectivenessandcharacteristicsofthefaulttolerantsystemwhichbasedon

functional programmingparadigm.

keywords: faulttolerantsoftware,looselycoupleddistributedsystems,parallelcomputation,functional

programming,resourceallocation