Ambient-Oriented Programmingusers.dcc.uchile.cl/~etanter/courses/mobility/amop.pdfProgramming Technology Lab - Vrije Universiteit Brussel Prof. Dr. Theo D’Hondt Jessie Dedecker,

Ambient-Oriented Programming

Designing an Object-Oriented Language for Ambient Intelligence

Presented at the JCC 2005. (c) E. Tanter, All Rights Reserved

Dr. Éric TanterUniversity of Chile

DCC/CWR

[email protected]

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mailto:[email protected]


Éric Tanter - JCC 2005 - [email protected]

Contents

• What is Ambient Intelligence (AmI)?

• OO Language Design for AmI

• AmbientTalk - A First OO Language for AmI

• Future Directions

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Credits

Wolfgang de Meuter“Move Considered Harmful -- A Language Design Approach to Distribution and Mobility in Open Networks”PhD Thesis, 2004

Programming Technology Lab - Vrije Universiteit BrusselProf. Dr. Theo D’Hondt

Jessie Dedecker, Tom Van Cutsem, Stijn MostinckxPhD students (VUB), AmbientTalk development

Sebastián GonzálezPhD student (UCL)

ORION: Open Reflective Infrastructure for Open NetworksProject DCC/CWR - VUB2006-2007

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Ambient Intelligence

A Peculiar Context for Application Development

[Dedecker+05b]

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Hardware Environment

• Advent of mobile networks

• wireless technologies (wifi, bluetooth)

• nomadic and ad hoc (aka. open networks)

• Mobile devices

• limited connection range and computational resources

• Ambient Intelligence

• European Council’s IST Advisory Group [ISTAG03]

• aka. ubiquitous computing [Weiser91], pervasive computing

what is fundamentally different?

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Autonomicity & Concurrency

Interconnected via ad hoc wireless networks

Communication

Autonomous Concurrent Devices

no central server natural concurrency

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Connection Volatility

Volatile Wireless Connections

Devices frequently disconnect

Failure

cannot assume stable connection

but tasks need to be done

exceptions are no more exceptional!7




Resource Discovery

Ambient Resources

Devices (dis)appear in the 'Ambient'

Spontaneous Service Discovery

I require a

printing service

I provide a

printing service

Discovery

resources depend on location

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Programming for AmI

• A robust AmI application must address these characteristics

• Current alternatives

• Middleware

• Distributed programming languages

DiscoveryFailureCommunication

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Middleware• RPC-based middleware

• Alice [Haarh+99], Dolmen [Reynolds+99]

• CORBA on lightweight devices

• no support for long disconnections

• Publish-subscribe middleware [Cugola+02]

• good for context-aware communication

• forces callback programming

• Tuple-space based middleware [Murphy+01]

• uncoupling in both time and space

• not object-oriented10


Distributed Languages

• Languages for LAN

• Emerald [Jul+88], Obliq [Cardelli95], etc.

• communication mechanisms assume reliable connection

• Languages for open networks

• Janus [Kahn+90], Salsa [Varela+98], E [Miller]

• pure asynchronous communication

• no support for resource discovery

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Position Statement

• Currently insufficient support for programming nomadic / ad hoc distributed systems

• low-level APIs, middleware, etc.

• can be done, but hard

• no dedicated abstractions for AmI specificities

• Need of dedicated languages: AmOP

[Dedecker+05]

“abstracting without hiding”

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Object-Oriented Languages for AmI

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Design Dimensions

object modelclass-based vs. prototype-based

static typing vs. dynamic typing

communication modelconcurrency model

communication primitives

failure handling

acquaintance management

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Why Classes Do Not Fitand neither static typing...

[Gonzales+04]

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OOP without classes??

object=

encapsulated state +

message passing

objects are goodencapsulation and polymorphism are

fundamental for highly dynamic environments

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OOP without classes???

• Classification of OOP languages [Wegner87]

• object-based (objects + messages)

• class-based (classes)

• object-oriented (classes + inheritance)

• prototype-based (objects + delegation/sharing)

• ...

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Fundamental Problem

Classesa static, implicit sharing mechanism of state and behaviour[Treaty of Orlando]

Distribution transparency is impossible to achieve in practice, and precisely because of that

impossibility, it is dangerous to provide the illusion of transparency.

[Guerraoui&Fayad99]

Open Networks

[Gonzales+04]

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State Sharing

• class attributes (eg. Java statics)

• semantics = value shared by all instances

not true under distribution!

public static-replicated synchronized Vector v;protected static-centralized String s;

Solution: add yet more keywords to Java...

or fix a choice and make it implicit in the language.

It’s no solution: a new node may appear with the same class, but with a different value....

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Code Sharing

• Exactly same issue with methods

A node containing the same class as another node may appear in the network, but with a different method

implementation...

Methods are part of a class’s state,just the same as class attributes.

If a method changes, the class is no longer the same, even if semantically it remains compatible.

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Transitive Closuresinstance-of link + subclass-of link

when an object is transmitted, its class and all superclasses must be transmitted too

(an object is not a self-contained entity!)

static typing

transmit argument-type classes, return-type class and exception-type classesand their transitive closures

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Conclusion on Classes

Classes (and static typing) are a barrier to adaptability

Classes are dangerous under distribution

sharing is important, but should be managed explicitly

prototype-based languages!

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Prototypes• eg. Self [Ungar+87]

• Self-contained objects

• state + code

• created ex-nihilo or by cloning

• Extension mechanism

• true delegation to parent

• Sharing mechanism

• parent sharing

• managed explicitly

• eg. traits

self

self

message forwarding

delegation

[Ungar+91]

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Communication Model

[Dedecker+05b]

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OO Concurrency ModelThread-based Actor model [Agha86]

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Communication Primitives• Blocking primitives are evil

• deadlocks & diminished availability of resources

Non-blocking Asynchronous Communication Primitives

Based on Actors (Agha, 1986)

send

transmit

receive

Communication

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Failure Recovery• Inconsistent states cannot be avoided

• need for reversibility

Reified Communication Traces

E.g. rollback strategies for failure recovery

agenda slot

available?yes

reservation

confirmed?

reserve slotAgendaActor

AgendaActor

Failure

AgendaActor

AgendaActor

rollback strategiesdelivery guarantees

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Acquaintance Management• No third party for communication (P2P)

• no explicit reference: distributed naming

Actors specify services required from and provided to the ambient

Provided service patterns

Required service patterns

description of service interface

Discovery

Reified Environmental Context

actors specify servicesrequired from the ambientprovided to the ambient

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Design Conclusions

Classless language, dynamically-typed

Actor model

Non-blocking communication primitives

Reified communication trace

Reified ambient context

C? C++? Java? C#?29



AmbientTalkA First AmOP Language

[Dedecker+05a]

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Tested and deployed on QTek9090 PocketPC smartphones

VM runs on Java J2SE and J2ME platforms

Dynamically typed language

Prototype-based object model

Actor-based concurrency model

Plug-and-play: no additional setup

VMs communicate via sockets over WLAN

AmbientTalk VM

Actors

jat

http://prog.vub.ac.be/amop

AmbientTalk

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«outbox»

«sentbox»

«inbox»

«rcvbox»

Communication Mailboxes reify actor-actor interaction

Communication

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«joinedBox»

«required»

«provided»

«disjoinedBox»

Discovery Mailboxes reify actor-ambient interaction

Discovery

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First-class Mailboxes

Meta-level events trapped using mailbox observers

interaction between mailboxes goverened by a metaobject protocol

onDisjoin

onJoin

onProcess

onReceipt

onTransmit

onSend

Metaobjects

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AmbientTalk VM

Actors

jat

PrintFileBehavior :: object({ printer : void; file : void;

new(aFile,dpi) :: copy({ printer := AmbientRef("Printer"); file := aFile });

printIt() :: { when(printer#print(file), { display("Doc Printed!”) }) }})

PrintFileActor(file,dpi) :: { actor(PrintFileBehavior.new(file,dpi))}

{ p: PrintFileActor(aFile,300); p#printIt() }

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Higher-level Constructs

• AmI is a moving target

• AmbientTalk is a testbed for AmOP experimentation

• Some higher-level constructs

• Non-blocking futures

• Application-specific message routing

• Group communication

• ...

[Dedecker+05a]

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Language-level Security

• Security must be addressed at all levels

• comm. channels, OS, language, application, user

• Extreme encapsulation principle

• objects subject to message passing alone

• no “omnipotent operators”

• But powerful object model

• cloning, extension, parent sharing, reflection

• eg. mirror methods [Tanter05]

[DeMeuter+05]

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Mobility

• Controversial feature

• Security-wise challenging

• A killer application? follow-me applications?

[Vallejos05]

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Open Infrastructure

• Reflective Virtual Machine for AmI

• Fine-tune tradeoffs/strategies at the VM level

• garbage collection

• failure recovery strategy

• partial reversible computation

• partial object matching for resource discovery

[ORION]

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Context Awareness

• Context-aware object references [VanCutsem+05]

• Context-oriented programming [Costanza+05]

• Context-aware aspects [Tanter+05]

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References (1)

[Agha86] G. Agha, Actors: a model of concurrent computation in distributed systems, MIT Press 1986.

[Cardelli95] L. Cardelli, Obliq: a language with distributed scope, Proceedings of POPL 1995.

[Costanza+05] P. Costanza, R. Hirschfeld, Language Constructs for Context-Oriented Programming, Proceedings of DLS 2005.

[Cugola+02] G. Cugola, H.-A. Jacobsen, Using Publish-Subscribe Middleware for Mobile Systems, SIGMOBILE Mob. Comp. Commun. 6(4), 2002.

[Dedecker+05a] J. Dedecker, S. Mostinckx, T. Van Cutsem, W. De Meuter, T. D’Hondt, AmbientTalk: A Small Reflective Kernel for Programming Mobile Network Applications, VUB TR 2005.

[Dedecker+05b] J. Dedecker, T. Van Cutsem, S. Mostinckx, W. De Meuter, T. D’Hondt, Ambient-Oriented Programming, OOPSLA Onward! 2005.

[DeMeuter+05] W. De Meuter, É. Tanter, S. Mostinckx, T. Van Cutsem, J. Dedecker, Flexible Object Encapsulation for Ambient-Oriented Programming, Proceedings of DLS 2005.

[Guerraoui&Fayad99] R. Guerraoui, M. E. Fayad, OO Distributed Programming is Not Distributed OO Programming, CACM 42(4), 1999.

[Gonzales+04] S. Gonzalez, W. De Meuter, K. Mens, T. D’Hondt, The Unavoidable Failure of Class-Based Languages n the Processor Cloud Era, ECOOP Workshop on Object-Oriented Language Engineering for the Post-Java Era, 2004.

[Haarh+99] M. Haarh, R. Cunningham, V. Cahill, Supporting CORBA Applications in a Mobile Environment, Proceedings MobiCom 1999.

[ISTAG03] ISTAG, Ambient Intelligence: From Vision to Reality, http://www.corids.lu/ist/istag.htm, 2003.

[Jul+88] E. Jul, H. Levy, N. Hutchinson, A. Black, Fine-grained Mobility in the Emerald System, ACM TCS 6(1), 1988.

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http://www.corids.lu/ist/istag.htm

http://www.corids.lu/ist/istag.htm

References (2)[Kahn+90] K.M. Kahn, V.A. Saraswat, Actors as a special case of concurrent constraint programming, Proceedings ECOOP/OOPSLA 1990.

[Miller] M. Miller, E: Open Source Distributed Capabilities, http://www.erights.org

[Murphy+01] A.L. Murphy, G.P. Picco, G.-C. Roman, Lime: A Middleware for Physical and Logical Mobility, Proceedings DCS 2001.

[ORION] Open Reflective Infrastructure for Open Networks, draft proposal for a bilateral project between the VUB Prog Lab and the DCC U. Chile, 2006-2007.

[Reynolds+99] P. Reynolds, R. Brangeon, DOLMEN - Service Machine Development for Open Long-Term Mobile and Fixed Network Environment. 1999.

[Tanter05] É. Tanter, Mirror Methods - Reconciling Reflection and Extreme Encapsulation, Proc. OT4AmI 2005.

[Tanter+05] É .Tanter, K. Gybels, M. Denker, A. Bergel, Context-Aware Aspects, DCC U.Chile TR 2005.

[Treaty of Orlando] H. Lieberman, L. Stein, D. Ungar, Treaty of Orlando, OOPSLA Add. 1987.

[Ungar+87] D. Ungar, R. Smith, Self: the Power of Simplicity, Proc. OOPSLA 1987.

[Ungar+91] D. Ungar, C. Chambers, B. Chang, U. Hölzle, Organizing Programs without Classes, Lisp Symb. Comp. 4(3), 1991.

[Vallejos05] J. Vallejos, Mobile Actors Supporting Reconfigurable Applications in Open P2P Networks, MSc Thesis, VUB, Belgium, 2005.

[Varela+98] C.A. Varela, G. Agha, What after Java? From Objects to Actors, Proceedings ICWWW 1998.

[VanCutsem+05] T. Van Cutsem, J. Dedecker, S. Mostinckx, W. De Meuter, Abstractions for Context-aware Object References, OOPSLA Workshop on Pervasive Computing, 2005.

[Wegner87] P. Wegner, Dimensions of Object-based Language Design, Proceedings OOPSLA 1987.

[Weiser91] M. Weiser, The Computer for the 21st Century, Scientific American 265(3) 1991.

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http://www.erights.org

http://www.erights.org

Documents

Ambient-Oriented Programmingusers.dcc.uchile.cl/~etanter/courses/mobility/amop.pdfProgramming Technology Lab - Vrije Universiteit Brussel Prof. Dr. Theo D’Hondt Jessie Dedecker,