Java Mobile Agents with Aglets

1. Java Mobile Agentswith Aglets Wolfgang Schreiner e9902261@student.tuwien.ac.at

2. Chapter 1 – Introduction to Mobile Agents

3. What is a Software Agent? • End-User Perspective – An agent is a program that assists people and acts on their behalf – Agents function by allowing people delegate work to them • System Perspective – An agent is a software object that is situated within an execution environment – possesses mandatory and orthogonal properties

4. What is a Mobile Agent? • Stationary Agent – executes only on the system where it begins execution – interacts with an agent using communication mechanisms • Mobile Agent – not bound to the system where it begins execution – has the ability to transport itself from one system in a network to another

5. Reasons for Mobile Agents • Reduce network load • Reduce network latency • Encapsulate protocols • Execute asynchronously and autonomously • Adapt dynamically • Are naturally heterogeneous • Are robust and fault-tolerant

6. Network Computing • Client-Server Paradigm – A server locally hosts services that provide access to resources and code that implements these services. • Code-on-Demand Paradigm – no preinstalled code on the client side • Mobile Agent Paradigm – hosts are allowed a high degree of flexibility

7. Mobile Agent Applications • Electronic Commerce • Personal assistance • Distributed information retrieval • Telecommunication network services • Workflow applications and groupware • Monitoring and notification • Parallel processing

8. Mobile Agent Systems • Java – Aglets – Odyssey – Concordia – Voyager • Others – Agent Tcl – Ara – TACOMA

9. Mobile Agent StandardizationMASIF • Agent management • Agent transfer • Agent and agent system names • Agent system type and location syntax

10. Chapter 2 – Elements of aMobile Agent System

11. Agent ...

12. ... and Place

13. Agent Behaviour (1) • Creation – Instantiation and identifier assignment – Initialization – Autonomous execution • Disposal – Preparing for disposal – Suspension of execution

14. Agent Behaviour (2) • Dispatching – Suspend, serialize, encode, transfer • Receiving – Receive, decode, de-serialize, resume execution • Agent Class Transfer – Class at destination – Class at origin – Code-on-demand

15. Communication

16. MASIF • MAFAgentSystemInterface – agent management tasks • MAFFinderInterface – agent naming service

17. Chapter 3 –Mobile Agents with Java

18. Java Agents - Benefits • Platform Independence • Secure Execution • Dynamic Class Loading • Multithread Programming • Object Serialization • Reflection

19. Java Agents - Drawbacks • Inadequate Support for Resource Control • No Protection of References • No Object Ownership of References • No Support for Preservation and Resumption of the Execution State

20. The Aglet Model • Basic Elements – aglet, proxy, context, identifier – creation, cloning, dispatching, retraction, disposal, activation/deactivation • Aglet Event Model – clone, mobility and persistence listener • Aglet Communication Model – Message, FutureReply, ReplySet

21. Aglet Package • class Aglet • interface AgletProxy • interface AgletContext • class Message • class FutureReply • class AgletID

22. Chapter 4 –Anatomy of an Aglet

23. Aglet Disposal • public final void Aglet.dispose(); • public void Aglet.onDisposing(); • Example: public class DisposalExample extends Aglet { public void onDisposing() { ... } public void run() { dispose(); } }

24. Delegation-Based Event Model • CloneEvent, MobilityEvent, PersistencyEvent • CloneListener, MobilityListener, PersistencyListener • CloneAdapter, MobilityAdapter, PersistencyAdapter

25. Cloning • public final Object Aglet.onClone(); • public final void Aglet.addCloneListener(CloneListener); • public final void Aglet.removeCloneListener(CloneListener); • public void CloneAdapter.onCloning(CloneEvent); • public void CloneAdapter.onClone(CloneEvent); • public void CloneAdapter.onCloned(CloneEvent);

26. Aglet Mobility • public final void Aglet.dispatch(URL); • public final void Aglet.addMobilityListener(MobilityListener); • public final void Aglet.removeMobilityListener(MobilityListener); • public void MobilityAdapter.onDispatching(MobilityEvent); • public void MobilityAdapter.onArrival(MobilityEvent); • public void MobilityAdapter.onReverting(MobilityEvent);

27. Persistence • public final void deactivate(long); • public final void Aglet.addPersistencyListener (PersistencyListener); • public final void Aglet.removePersistencyListener (PersistencyListener); • public void PersistencyAdapter.onDeactivating (PersistencyEvent); • public void PersistencyAdapter.onActivation (PersistencyEvent);

28. Events • CloneEvent • MobilityEvent – public URL MobilityEvent.getLocation(); • PersistencyEvent – public long PersistencyAdapter.getDuration();

29. Chapter 5 –Aglet Context

30. Aglet Creation • Code and Code Base • Code Base and Class Mobility • Initialization Argument

31. Proxy Retrieval • Proxy Iterator – public abstract Enumeration AgletContext.getAgletProxies(); • Getting a Local Proxy – public abstract AgletProxy AgletContext.getAgletProxy(AgletID); • Getting a Remote Proxy – URL as additional parameter

32. Aglet Retraction • public abstract AgletProxy AgletContext.retractAglet(URL,AgletID); • Example: AgletID aid=proxy.getAgletID(); Proxy.dispatch(dest); getAgletContext().retractAglet(dest,aid);

33. Context Properties • public abstract Object AgletContext.getProperty(String); • public abstract Object AgletContext.getProperty(String,Object); • public abstract void AgletContext.setProperty(String,Object);

34. Chapter 6 –Aglet Messaging

35. Simple Messaging • public Object AgletProxy.sendMessage(Message); • public boolean Aglet.handleMessage(Message);

36. The Message Class • Message Creation – public Message(String [,…] ); • Receiving Messages – getArg, setArg, getKind, sameKind • Replying to Messages – public void Message.sendReply(); – public void Message.sendException(Exception);

37. Getting the Reply

38. Message Management • Serialized Message Handling • Message Priorities • Parallel Message Handling • Synchronized Message Handling

39. Multicasting • public final void Aglet.subscribeMessage(String); • public final void Aglet.unsubscribeMessage(String); • public final void Aglet.unsubscribeAllMessages(); • public ReplySet AgletContext.multicastMessage(Message);

40. Receiving Multiple Replies • public boolean ReplySet.hasMoreReplies(); • public FutureReply ReplySet.getNextFutureReply(); • public boolean ReplySet.addFutureReply(FutureReply);

41. Chapter 7 –Aglet Collaboration

42. Aglet Proxy • Cloning • Disposal • Dispatching • Deactivation and Activation • Aglet Information

43. Controlling an Aglet

44. Finding an Aglet • Search • Logging • Registration • AgletFinder – Lookup: NAME – Register: NAME & PROXY – Unregister: NAME

45. Aglets in Parallel Execution

46. Chapter 8 –Agent Design Patterns

47. Design Pattern Classification • Traveling Patterns – Itinerary, Forward, Ticket • Task Patterns – Master-Slave • Interaction Patterns – Meeting, Locker, Messenger, Finder, Organized Group

48. Chapter 9 –Inside Aglets

49. Architectural Overview • Core Framework – Initialization and (de-)serialization – Class loading and transfer – Aglet references and garbage collection • Management Components – PersistencyManager – CacheManager – SecurityManager • Communication Layer

50. Aglet Object Structure