Agent behaviours (part 3)
Agent communication (part 1)
Fabiano Dalpiaz
Agent-Oriented Software Engineering (AOSE) 2009-10
Behaviour execution in dedicated
thread
• JADE scheduler changes beahviour only when an
action() method returns
– Pros: efficiency and scalability
– Cons: What if an action() method never returns or takes
long time?
• JADE allows for threaded execution of a behaviour
– A dedicated thread is given to the behaviour
– How to?
• Create a ThreadedBehaviourFactory
• When adding a behaviour b, call addBehaviour(tbf.wrap(b))
Behaviour execution in dedicated
thread
• Be careful when using threaded behaviours
– The method removeBehaviour() of Agent (you can guess
its semantics) does not work with threaded behaviours
– Threaded behaviours must be explicitly killed
• Take the thread by calling the getThread() method of
ThreadedBehaviourFactory
• Call the thread's interrupt() method
– Synchronization is not handled by JADE
• If the threaded behaviour uses shared resources, the
programmer is in charge of concurrency management
Exercise 1: Concurrent Behaviours
• Create one agent
– One shared integer variable value
– Its top-level behaviour is a parallel one
– The parallel behaviour has three sub-behaviours
• A wakeup behaviour which deletes the agent after 12 sec
• Two identical behaviours that cyclically
– Increment value, wait for n milliseconds, print value
– The actual value of n is passed in the constructor
» Behaviour 1: 2000 ms
» Behaviour 2: 3000 ms
– Behaviour 2 is executed in a dedicated thread
– HINT: you might have troubles with CyclicBehaviour!!!
Agent communication
• Agents typically are not isolated
– They operate in multi-agent systems!
• Agents communicate by messaging
– What is a message?
– How is a message defined?
– What is a protocol?
Agent communication basics
• JADE agents have communication capabilities
– The adopted paradigm is asynchronous message passing.
• Each agent has a sort of mailbox (the agent message
queue)
– JADE posts into the mailbox the messages sent by other
agents
– Whenever a message is posted in the message queue the
receiving agent is notified
– The programmer decides when to get the message from the
message queue
6
Messages: the reference model
Software
Agent
Agent Platform
Agent
Management
Directory
System
Facilitator
ACC
Internal Platform Message Transport
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F. Dalpiaz – AOSE 2008-09
How do agents communicate?
• Messages exchanged by JADE agents have a format
specified by the FIPA ACL (Agent Communication
Language)
– Instances of the jade.lang.acl.ACLMessage class.
• JADE provides methods to get and set all the fields
defined by the ACL language
–
–
–
–
–
–
–
get/setPerformative()
get/setSender()
add/getAllReceiver()
get/setLanguage()
get/setOntology()
get/setContent()
…
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F. Dalpiaz – AOSE 2008-09
Anatomy of an ACL message
FIPA performatives
• inform: Tell another agent something.
• confirm: The sender confirms to the receiver the truth
of the content.
• disconfirm: The sender confirms to the receiver the
falsity of the content.
• not-understood: Sent when the agent did not
understand the message.
• propagate: Asks another agent to forward this same
propagate message to others.
FIPA performatives
• query-if: The action of asking another agent whether
or not a given proposition is true.
• inform-if: Used as content of request to ask another
agent to tell us is a statement is true or false.
• query-ref: The action of asking another agent for the
object referred to by an referential expression.
• inform-ref: Like inform-if but asks for the value of the
expression.
FIPA performatives
• request: The sender requests the receiver to perform
some action.
• request-when: The sender wants the receiver to
perform some action when some given proposition
becomes true.
• request-whenever: The sender wants the receiver to
perform some action as soon as some proposition
becomes true and thereafter each time the proposition
becomes true again.
FIPA performatives
• agree: The action of agreeing to perform a requested
action made by another agent. Agent will carry it out.
• refuse: The action of refusing to perform a given
action, and explaining the reason for the refusal.
• cancel: Agent wants to cancel a previous request.
• failure: Tell the other agent that a previously
requested action failed.
FIPA performatives
• cfp: Agent issues a call for proposals. It contains the
actions to be carried out and any other terms of the
agreement.
• propose: Used as a response to a cfp. Agent proposes
a deal.
• accept-proposal: The action of accepting a previously
submitted propose to perform an action.
• reject-proposal: The action of rejecting a proposal to
perform some action during a negotiation.
FIPA performatives
• proxy: The sender wants the receiver to select target
agents denoted by a given description and to send an
embedded message to them.
• subscribe: The act of requesting a persistent intention
to notify the sender of the value of a reference, and to
notify again whenever the object identified by the
reference changes.