Glint, Breeding Mobile Ambients with Actors - Imperial College London

122 Pages·2006·0.93 MB·English

by  Matthew Sackman

UniversityofLondon
ImperialCollegeofScience,TechnologyandMedicine
DepartmentofComputing
Glint:
Breeding Mobile Ambients
with Actors
Final Report
Matthew Sackman
Supervisor: Susan Eisenbach
Second Marker: Sophia Drossopoulou
Copyright©MatthewSackman,2006. Allrightsreserved.
Copyright©MatthewSackman,2006. Allrightsreserved.
[email protected]
Thisreport,allsourcecodeandotherdocumentationrelatingtothisprojectisavailablefrom
http://www.wellquite.org/glint/
TypesetinLATEX2ε usingMonotypePlantin®andAdobeMyriad®
ThisreportisbroughttoyoubyEmacs,DasKeyboard,TCP/IPandtheletterQ.

Abstract
Software Engineering is facing a crisis. Hardware designers are no longer able
to make ever faster single-threaded CPUs and are instead building CPUs with
thread-level parallelism. Simultaneously, clusters of computers are becoming far
morepopularforbuildinghighperformancesystemsbutmakinggooduseofthese
parallel and distributed systems is difficult to achieve with current tools. Mobile
computationisalsobecomingincreasinglyimportantascomputersshrinkinsize
andbecomephysicallymoreportable. Engineeringapplicationsthatcanmigrate
betweendevicesandshareresourcesisaverydifficulttaskgiventhecurrenttools,
platformsandlanguagesavailable.
The methodologies and techniques for addressing the issues of concurrent,
distributedandmobilecomputationarebadlyunderdevelopedandunsuitablefor
thelargesoftwaresystemsbeingbuilttoday. Typicallockingmechanismsinmod-
ern programming languages are problematic and unsafe to use in large software
systemsbecauseoftheinabilitytoanalysesuccessfullytheiruseandbecausethey
arenotsafeincomposition. Distributedandmobilecomputationissimilarlybadly
addressedbymostprogramminglanguageswhichoftenpresentcomplexandmis-
leadingnotionsofmobility.
ThisreportpresentstheGVM,aninterpreterfortheSafeBoxedAmbient
calculus of Merro and Sassone. Ambient calculi are designed to model concur-
rent,distributedandmobilecomputationbutwithsomeadaptationIusethemas
anassemblylanguageforavirtualmachine. IaddmobilitytotheActorparadigm
of Hewitt and Agha and present the G language based on the Actor model.
The Actor model was similarly designed with concurrency and distribution in
mind but is a more powerful abstraction, is more expressive than the Ambient
calculi and is hence more suited for programming. I then present a compiler
which translates from the G language to the Safe Boxed Ambient calculus
whichcanthenbeinterpretedbytheGVM.
Thiscompletetoolchainofalanguage,compilerandinterpretercontributesto
therangeoftoolsandtechniquesthatareavailablefortacklingtheparallelarchi-
tecturesandthechallengesofmobileanddistributedcomputation. Theresulting
programming model is better suited for these purposes and more concisely and
powerfullyexpressesmovementthanexistinglanguagessuchasJ.


Acknowledgements
Thisprojectwouldnothavebeenpossiblewithouttheinputfrommany,ofwhom
here,Ihavememorytothankjustafew. Firstlymysupervisor,SusanEisenbach
forallowingmeconsiderablefreereigninmyworkonthisprojectandfortelling
mewhentowalkawaybeforehospitalisationbecamenecessary.
Many thanks to Amy for tolerating the endless late nights, deterioration of
my ability to hold a normal conversation and general coping with my devolution
into something socially more primitive. Thanks too for Sophia Drossopoulou’s
insistencethattheimplementationofahighlyconcurrentandcomplexsystemis
notsomethingtotrivialiseaway.
Tim Wood for superb knowledge of J as ever along with Tristan Allwood,
Marc Hull, Steve Zymler, Francis Russell and others for inspiring and insightful
conversationandpoliticaldebate. ThankstotheSgroupfortheircriticaland
goodnaturedgrillingandthankstoWillKnottenbeltforpermittingmeaccessto
his high performance cluster. Thanks too to the French Alps for being suitably
covered in snow and for providing a sufficiently soft landing after an eight-foot
unsighteddrop...


Contents
1 Introduction 
1.1 BackgroundandContext . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 ReportStructure . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 AmbientCalculi 
2.1 MobileAmbients . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1 Communication. . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.2 ObjectiveandSubjectivemoves . . . . . . . . . . . . . . . . . . . . .
2.1.3 Objectiveopen . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 BoxedAmbients . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 CommunicationInterference . . . . . . . . . . . . . . . . . . . . . . .
2.4 TypingAmbients . . . . . . . . . . . . . . . . . . . . . . . . . . . 
2.4.1 TypingMobileAmbients . . . . . . . . . . . . . . . . . . . . . . 
2.4.1.1 ExchangeTypes . . . . . . . . . . . . . . . . . . . . . . . . 
2.4.1.2 OpeningControl . . . . . . . . . . . . . . . . . . . . . . . . 
2.4.1.3 CrossingControl. . . . . . . . . . . . . . . . . . . . . . . . 
2.4.2 TypingBoxedAmbients. . . . . . . . . . . . . . . . . . . . . . . 
2.4.2.1 Typingprocesscommunication . . . . . . . . . . . . . . . . . . 
2.4.2.2 TypingAmbientmobility. . . . . . . . . . . . . . . . . . . . . 
2.5 TheChannelAmbientSystem . . . . . . . . . . . . . . . . . . . . . . 
2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3 Actors 
3.1 BasicConcepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.2 BenefitsofActors. . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.2.1 SharedMutableState. . . . . . . . . . . . . . . . . . . . . . . . 
3.2.1.1 TransactionalMemory. . . . . . . . . . . . . . . . . . . . . . 
3.2.2 UnsharedMutableState. . . . . . . . . . . . . . . . . . . . . . . 
3.3 Implementations . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.3.1 S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.3.2 E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.3.3 S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
3.3.3.1 ContinuationBasedProgramming . . . . . . . . . . . . . . . . . 
3.3.3.2 TokenPassingContinuations . . . . . . . . . . . . . . . . . . . 
3.3.3.3 JoinContinuations . . . . . . . . . . . . . . . . . . . . . . . 
3.3.3.4 FirstClassContinuations. . . . . . . . . . . . . . . . . . . . . 
3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4 TheGLINTVM 
4.1 WhichAmbientcalculus? . . . . . . . . . . . . . . . . . . . . . . . . 
4.1.1 FromLATEXtoA . . . . . . . . . . . . . . . . . . . . . . . . 

4.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.3 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.3.1 FromStatictoDynamic. . . . . . . . . . . . . . . . . . . . . . . 
4.3.2 Substitutions,Namesandα-conversions. . . . . . . . . . . . . . . . . 
4.3.3 Hosts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.4 TestingNon-determinism. . . . . . . . . . . . . . . . . . . . . . . . 
4.5 ProcessContainers . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.5.1 Ambients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.5.2 Restriction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.6 Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.7 PairingsandRendezvous . . . . . . . . . . . . . . . . . . . . . . . . 
4.7.1 Mobility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.7.2 Communication. . . . . . . . . . . . . . . . . . . . . . . . . . 
4.7.2.1 LocalInput,LocalOutput . . . . . . . . . . . . . . . . . . . . 
4.7.2.2 LocalInput,ParentOutput . . . . . . . . . . . . . . . . . . . . 
4.7.2.3 ParentInput,LocalOutput . . . . . . . . . . . . . . . . . . . . 
4.7.2.4 LocalInput,ChildOutput . . . . . . . . . . . . . . . . . . . . 
4.7.2.5 ChildInput,LocalOutput . . . . . . . . . . . . . . . . . . . . 
4.7.3 ModellingthePairingMechanism . . . . . . . . . . . . . . . . . . . 
4.8 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.9 Inter-hostMobility . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.10 InteractingwiththeRealWorld . . . . . . . . . . . . . . . . . . . . . 
4.10.1 Println. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.10.2 Readln. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
4.11 TechnologiesEmployed . . . . . . . . . . . . . . . . . . . . . . . . 
4.12 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
5 TheGLINTLanguage 
5.1 TheSuitabilityofActors . . . . . . . . . . . . . . . . . . . . . . . . 
5.2 ModifyingActors. . . . . . . . . . . . . . . . . . . . . . . . . . . 
5.3 ComponentsoftheGLanguage . . . . . . . . . . . . . . . . . . . 
5.3.1 ActorTypes,VariablesandAssignment . . . . . . . . . . . . . . . . . 
5.3.2 ActorInstancesandSingletonActors . . . . . . . . . . . . . . . . . . 
5.3.3 MethodCalls. . . . . . . . . . . . . . . . . . . . . . . . . . . 
5.3.4 WhereClauses . . . . . . . . . . . . . . . . . . . . . . . . . . 
5.3.5 BecomingDeath . . . . . . . . . . . . . . . . . . . . . . . . . 
5.3.6 SimpleMethods. . . . . . . . . . . . . . . . . . . . . . . . . . 
5.3.7 ComplexMethods . . . . . . . . . . . . . . . . . . . . . . . . . 
5.4 Puttingitalltogether. . . . . . . . . . . . . . . . . . . . . . . . . . 
5.4.1 AnonymousInnerActors . . . . . . . . . . . . . . . . . . . . . . 
5.4.2 Movement. . . . . . . . . . . . . . . . . . . . . . . . . . . . 
5.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
6 TheGLINTCompiler 
6.1 TransformingtheAST. . . . . . . . . . . . . . . . . . . . . . . . . 
6.1.1 CheckingMethodDefinitions. . . . . . . . . . . . . . . . . . . . . 
6.1.2 CheckingforVariableDefinitions . . . . . . . . . . . . . . . . . . . 
6.1.3 CheckingforCyclesinVariableDefinitions. . . . . . . . . . . . . . . . 
6.1.4 RewritingPredicatesandConstructorCalls . . . . . . . . . . . . . . . 
6.1.5 RewritingInlineStuff. . . . . . . . . . . . . . . . . . . . . . . . 
6.1.6 MovingtheWhereClauses. . . . . . . . . . . . . . . . . . . . . . 
6.1.7 FurtherModifyingPredicates. . . . . . . . . . . . . . . . . . . . . 
6.1.8 ReorderingVariableDefinitions . . . . . . . . . . . . . . . . . . . . 
6.1.9 CreatingAmbientGenerators. . . . . . . . . . . . . . . . . . . . . 

6.2 EncodingintoAmbients . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.1 BasicPropertiesoftheEncoding . . . . . . . . . . . . . . . . . . . 
6.2.2 MarshallingCallers . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.3 ChangingBehaviours. . . . . . . . . . . . . . . . . . . . . . . . 
6.2.4 ReceivingMethodCalls . . . . . . . . . . . . . . . . . . . . . . . 
6.2.5 MethodCallers . . . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.6 EncodingBecome . . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.7 LocalMethodCalls . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.8 AnonymousInnerActors . . . . . . . . . . . . . . . . . . . . . . 
6.2.9 MethodswithPredicates. . . . . . . . . . . . . . . . . . . . . . . 
6.2.10 TrueandFalse. . . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.11 EncodingNumbers . . . . . . . . . . . . . . . . . . . . . . . . 
6.2.12 EqualityTesting . . . . . . . . . . . . . . . . . . . . . . . . . 
6.3 TechnologiesEmployed . . . . . . . . . . . . . . . . . . . . . . . . 
6.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
7 Evaluation 
7.1 Two-tieredDesign . . . . . . . . . . . . . . . . . . . . . . . . . . 
7.2 TheGVM. . . . . . . . . . . . . . . . . . . . . . . . . . . . 
7.3 TheGLanguage . . . . . . . . . . . . . . . . . . . . . . . . . 
7.4 TheChannelAmbientSystem . . . . . . . . . . . . . . . . . . . . . . 
7.5 Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
7.5.1 CustomGVMCode . . . . . . . . . . . . . . . . . . . . . . 
7.5.1.1 Sequential-SequentialCommunication. . . . . . . . . . . . . . . . 
7.5.1.2 Parallel-SequentialCommunication . . . . . . . . . . . . . . . . . 
7.5.1.3 Parallel-ParallelCommunication . . . . . . . . . . . . . . . . . . 
7.5.1.4 LocalMovement . . . . . . . . . . . . . . . . . . . . . . . . 
7.5.1.5 Inter-hostMovement . . . . . . . . . . . . . . . . . . . . . . 
7.5.2 GeneratedGVMCode . . . . . . . . . . . . . . . . . . . . . 
7.5.2.1 MethodCalls . . . . . . . . . . . . . . . . . . . . . . . . . 
7.5.2.2 LocalMethodCalls . . . . . . . . . . . . . . . . . . . . . . . 
7.5.2.3 Inter-hostMethodCalls . . . . . . . . . . . . . . . . . . . . . 
7.5.3 ComparisonwithJ . . . . . . . . . . . . . . . . . . . . . . . 
7.5.4 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 
8 Conclusion 
8.1 Ambients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.2 Actors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3 FutureWork. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3.1 ImprovingtheGVM . . . . . . . . . . . . . . . . . . . . . . 
8.3.1.1 GarbageCollection . . . . . . . . . . . . . . . . . . . . . . . 
8.3.1.2 DebuggingandInspection . . . . . . . . . . . . . . . . . . . . 
8.3.1.3 SecurityofCommunicationandInter-SystemInteraction. . . . . . . . . 
8.3.1.4 TypingsintheGVM. . . . . . . . . . . . . . . . . . . . . 
8.3.2 ExtendingtheGLanguage . . . . . . . . . . . . . . . . . . . . 
8.3.2.1 AsynchronousMessages . . . . . . . . . . . . . . . . . . . . . 
8.3.2.2 Interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3.2.3 TypeSystems . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3.2.4 NamedParameters . . . . . . . . . . . . . . . . . . . . . . . 
8.3.2.5 Currying. . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3.2.6 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
8.3.2.7 LibrariesandErrorHandling . . . . . . . . . . . . . . . . . . . 
8.3.3 RedesigningtheEncoding . . . . . . . . . . . . . . . . . . . . . . 
8.4 FinalThoughts. . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Bibliography 
A MeaninglessMetrics 
B EmailServer 
B.1 Email . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
B.2 Mailbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
B.3 CentralEmailServer . . . . . . . . . . . . . . . . . . . . . . . . . 
B.4 ComparingtoJ . . . . . . . . . . . . . . . . . . . . . . . . . . 
C LTSATutorial 
D UsingtheGLINTVMandCompiler 
D.1 UsingtheGVM . . . . . . . . . . . . . . . . . . . . . . . . . 
D.2 UsingtheGCompiler . . . . . . . . . . . . . . . . . . . . . . . 
