JADE: Parallelism

1
JADE Parallelism Behaviours

• Sensor Web TITAN Research
• 3/12/2009

2
Behaviours

• Agents operate independently, execute in parallel
• Assign a Java Thread to each agent
• But also need parallelism within each agent
• An agent may be involved in several tasks
• Possible solution additional threads for each
  concurrent agent activity
• But Java Threads werent designed for large-scale
  parallelism

3
Behaviours

• To support efficiently parallel activities within
  an agent, Jade introduced Behaviours
• A behaviour is basically an Event Handler,
  describing how an agent reacts to an event
• An event is a relevant change of state
• E.g., a reception of a message or a Timer
  interrupt

4
Implementing a behaviour

• A behaviour is an object of a class that extends
  jade.core.behaviours.Behaviour.
• A class extending Behaviour must implement some
  methods
• action() defines the operations to be performed
  when the behaviour is in execution
• done() specifies whether a behaviour has
  completed, through the boolean value it returns

5
Behaviours (Important Notes)

• Behaviour actions are methods
• Executed one after the other by the agent's
  thread after events
• Cant pause without blocking all other activity
  within the agent
• So each Behaviour execution corresponds to ONE
  SINGLE instantaneous active phase
• To implement long-term activities (e.g., a
  negotiation), must provide as many Behaviours as
  there are active phases

6
Implementing a behaviour

• To implement an agent-specific task
• define 1 or more Behaviour subclasses,
• instantiate them, and
• add the behaviour objects to the agents task
  list
• using addBehaviour(Behaviour)method

7
Agent1 Example

• 2 identical behaviours that show parallelism
• Prints a message with the elapsed time and agent
  name
• Create instance of the behaviour
• Add behaviour using addBehaviour(Behaviour)
• addBehaviour( new Looper( this, 300 ) )

8
Agent1 Example (code)

• public class Agent1 extends Agent
• protected void setup()
• addBehaviour( new Looper( this, 300 ) )
  addBehaviour( new Looper( this, 500 ) )
• // Action method of Looper behaviour
• public void action()
• System.out.println( tab (System.currentTimeMill
  is()- t0)/1010 " " myAgent.getLocalName()
  )
• block( dt )
• n

9
Complete CodeFile Agent1.java

• import jade.core.Agent
• import jade.core.behaviours.
• public class Agent1 extends Agent
• protected void setup()
• addBehaviour( new Looper( this, 300 ) )
• addBehaviour( new Looper( this, 500 ) )

10
Complete CodeLooper.java

• import jade.core.Agent
• import jade.core.behaviours.
• class Looper extends SimpleBehaviour
• static String offset ""
• static long t0 System.currentTimeMillis()
  
• String tab ""
• int n 1
• long dt

Continued
11

• public Looper( Agent a, long dt)
• super(a)
• this.dt dt
• offset " "
• tab new String(offset)
• public void action()
• System.out.println( tab
• (System.currentTimeMillis()-t0)/1010 " "
  
• myAgent.getLocalName() )
• block( dt )
• n
• public boolean done() return ngt6

12
Output from Agent1

• gt java jade.Boot aaaAgent1
• 0 aaa
• 0 aaa
• 300 aaa
• 510 aaa
• 620 aaa
• 920 aaa
• 1010 aaa
• 1220 aaa
• 1520 aaa
• 1530 aaa
• 2020 aaa
• 2530 aaa

13
Output from two Agent1 agents

• gt java jade.Boot aaAgent1 zzzzzAgent1
• 0 zzzzz
• 0 aa
• 10 zzzzz
• 10 aa
• 300 zzzzz
• 310 aa
• 510 zzzzz
• 510 aa
• 610 zzzzz
• 610 aa
• 910 zzzzz
• 920 aa

14
Output from two Agent1 agents (cont.)

• 1020 zzzzz
• 1020 aa
• 1220 zzzzz
• 1220 aa
• 1520 zzzzz
• 1520 aa
• 1520 zzzzz
• 1530 aa
• 2030 zzzzz
• 2030 aa
• 2530 zzzzz
• 2530 aa

15
block(dt) vs. sleep(dt)

• block(dt) sets a delay for the behaviours next
  execution
• Does not block the execution of the behaviour
• sleep(dt) suspends the execution of the thread
• If that thread is put to sleep, then all activity
  for that agent stops

16
Bad1 Example

• Try to solve a more complex sequencing problem in
  a variety of ways
• Combine a sequence of 2 actions with the above
  Looping behaviour
• In the sequential part, we want our agent to
• wait 0.25 sec then print out a first message
• wait 0.5 sec and print out a second message
• then terminate
• The next implementation is an incorrect example
  of parallelism
• Uses block(dt) along with a Looper behaviour

17
Bad1 Example (code)

• public class Bad1 extends Agent
• protected void setup()
• addBehaviour( new TwoStep() )
• addBehaviour( new Looper( this, 300 ) )
• // TwoStep Behaviour
• import jade.core.behaviours.SimpleBehaviour
• class TwoStep extends SimpleBehaviour
• public void action()
• block(250)
• System.out.println( "--- Message 1 --- "
  )
• block(500)
• System.out.println( " - message 2 " )

18
Output from Bad1

• gt java jade.Boot johnBad1
• --- Message 1 ---
• message 2
• 10 john
• 310 john
• 620 john
• 920 john
• 1220 john
• 1530 john

19
Block2 Example

• A single behaviour, BlockTwice
• 2 block statements
• Prints out the clock at the beginning of the
  action and after each block()

20
Block2 Example (code)

• public class Block2 extends Agent
• protected void setup()
• addBehaviour( new BlockTwice() )
• class BlockTwice extends SimpleBehaviour
• static long t0 System.currentTimeMillis()
• public void action()
• System.out.println( "Start "
  (System.currentTimeMillis()-t0) )
• block(250)
• System.out.println( " after block(250) "
  (System.currentTimeMillis()-t0) )
• block(1000)
• System.out.println( " after block(1000) "
  (System.currentTimeMillis()-t0) )
• System.out.println()

21
Output from Block2

• gt java jade.Boot tomBlock2
• Start 1
• after block(250) 7
• after block(1000) 9
• Start 258
• after block(250) 261
• after block(1000) 263
• Start 512
• after block(250) 515
• after block(1000) 517
• Start 767
• after block(250) 769
• after block(1000) 771

22
Bad3 Example with sleep()

• Incorrect example of parallelism
• Uses sleep(dt)method
• An agent only has 1 Thread, shared by the
  behaviours
• If that Thread is put to sleep anywhere, then all
  activity for that agent stops

23
Bad3 Example with sleep() (code)

• class TwoStep extends SimpleBehaviour
• public void action()
• try
• System.out.println( "--- TwoStep
  start " ...time )
• Thread.sleep(200)
• System.out.println( " -- Message 1
  --- " ...time )
• Thread.sleep(500)
• System.out.println( " - message 2
  " ...time )
• catch (Exception e)
• private int n 0
• public boolean done() return n gt 2
  

24
Output from Bad3

• gt java jade.Boot maryBad3
• --- TwoStep start 20
• -- Message 1 --- 220
• - message 2 720
• 700 mary
• --- TwoStep start 730
• -- Message 1 --- 930
• - message 2 1430
• --- TwoStep start 1440
• -- Message 1 --- 1640
• - message 2 2140
• 2120 mary
• 2430 mary
• 2730 mary
• 3040 mary
• 3340 mary

25
Updated Agent2

• If an activity is made up of a sequence of active
  phases with pauses in between, use 1 Behaviours
  for every active phase
• Need 2 behaviours to print out the 2 messages
• Ideally, schedule newly created behaviours for
  some future time
• In the behaviour which prints out Msg1, we
  schedule the behaviour which prints out Msg2 to
  occur 0.5 sec later
• But block() can't be used to schedule other
  behaviours
• Just postpones the next execution of the current
  behaviour
• Solution Use a state variable to distinguish
• the 1st execution of a behaviour (when we execute
  block(dt)) from
• the next execution (which occurs dt msec later)

26
Updated Agent2 (code)

• class Step1 extends SimpleBehaviour
• int state 0
• public void action()
• if (state0) block( 200 )
• else if (state1)
• System.out.println( "--- Message
  1 --- " )
• addBehaviour( new Step2() )
• state
• public boolean done() return state gt
  1

27
Updated Agent2 (code) - continued

• class Step2 extends SimpleBehaviour
• int state 0
• public void action()
• if (state0)
• block( 600 )
• else
• System.out.println( " -
  message 2 " )
• doDelete() // applies to the
  Agent
• state
• public boolean done() return stategt1
  

28
Output from Updated Agent2

• gt java jade.Boot harryAgent2
• 0 harry
• --- Message 1 ---
• 340 harry
• 640 harry
• - message 2

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Agent3 (Final version)

• Creates a finite state machine
• Uses a switch to select the actions corresponding
  to each state

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Agent3 (Final version) (code)

• class TwoSteps extends SimpleBehaviour
• int state 1
• public void action()
• switch( state )
• case 1
• block( 200 )
• break
• case 2
• System.out.println( "--- Message
  1 --- " )
• block( 800 )
• break
• case 3
• System.out.println( " -- message
  2 --" )
• finished true

31
Output from Agent3

• gt java jade.Boot aliceAgent3
• 0 alice
• --- Message 1 ---
• 340 alice
• 640 alice
• 950 alice
• -- message 2 --

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Complete CodeAgent3.java

• The program ends normally get back to the shell
  prompt without CTL-C
• Provided the agent with a takeDown() method
• Called automatically when an agent is deleted
• Most often, this is where an agent removes its
  entries from various directories
• Here we just stop the container and terminate the
  program with System.exit(0)

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• import jade.core.Agent
• import jade.core.behaviours.
• public class Agent3 extends Agent
• protected void setup()
• addBehaviour( new TwoSteps() )
• addBehaviour( new Looper( this, 300 ) )
• protected void takeDown()
• System.exit(0)

Continued
34

• class TwoSteps extends SimpleBehaviour
• int state 1
• public void action()
• switch( state)
• case 1
• block( 200 )
• break
• case 2
• System.out.println( "--- Message
  1 --- " )
• block( 800 )
• break

Continued
35

• case 3
• System.out.println( " -- message
  2 --" )
• finished true
• doDelete() // applies to the
  Agent
• state
• private boolean finished false
• public boolean done() return
  finished

36
Negotiation example w/ Behaviours

• Consider a negotiation (sending offers, waiting
  for counter-offers and finally reaching
  agreement)
• This activity consists of an alternation of
• active phases - when the agent decides what to
  do and sends messages
• passive phases - when the agent waits for an
  answer.