Demo: Using JMX to probe into Jason Agent execution

[mindcrime]

Hi all, thought that today I'd try sharing something instead of bothering people with my own questions. It's all related though.. in service of figuring out some stuff about how things work in the bowels of Jason at Agent execution time I threw together a little thing with a custom JMX MBean and a custom Agent class, where I can jam properties into the MBean and inspect them with JConsole, as well as blocking execution at a point until I invoke an operation on the MBean.

In some ways this isn't too different than what you can accomplish with some combination of the MindInspector and the debug mode ExecutionControl class, but this setup is just more natural to way I think and work. Maybe some other folks will find this valuable for something, especially in regards to learning Jason.

Full runnable example with all source code can be found at this repo

The basic concept is this. I created a custom Agent class, and overrode the selectEvent and selectIntention methods. In selectEvent I only do some extra logging, but in selectIntention I add the AgentStats MBean if it's not already in the PlatformMBeanServer, and set the current cycle number and the list of available Intentions. If the MBean is already there I just updated the attributes with the updated values. Then I block execution indefinitely until the MBean's "proceed" flag toggles to true (it resets immediately afterward, so every iteration will block when using this approach).

JMXAgent.java

package agent;

import java.lang.management.ManagementFactory;
import java.util.Queue;
import java.util.logging.Logger;

import javax.management.Attribute;
import javax.management.InstanceNotFoundException;
import javax.management.MBeanAttributeInfo;
import javax.management.MBeanInfo;
import javax.management.MBeanServer;
import javax.management.ObjectName;

import jason.asSemantics.Agent;
import jason.asSemantics.Event;
import jason.asSemantics.Intention;
import mbean.AgentStats;
import mbean.AgentStatsMBean;

public class JmxAgent extends Agent
{
	private Logger logger = Logger.getLogger( JmxAgent.class.getName() );

	
	@Override
	public Event selectEvent( Queue<Event> events )
	{

		// Iterator eventIter = events.iterator();
		StringBuilder sb = new StringBuilder();
		for( Event event : events )
		{
			sb.append(  event.toString() + "\n" );
		}
		
		logger.info(  "selectEvent called. Stack of Events is currently: \n" + sb.toString() );
		
		return super.selectEvent( events );
	}
	
	
	@Override
	public Intention selectIntention( Queue<Intention> intentions )
	{
		try
		{
			MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

			ObjectName agentStatsMBeanName = new ObjectName("org.fogbeam.example.jason.jmx:type=AgentStats");
		
			MBeanInfo agentStatsMBeanInfo = null;
			try
			{
				agentStatsMBeanInfo = mbs.getMBeanInfo( agentStatsMBeanName );
			}
			catch( InstanceNotFoundException infe )
			{
				// infe.printStackTrace();
				logger.info(  "Existing MBean instance not found!" );
			}
			
			AgentStatsMBean agentStatsMBean = null;

			int cycleNumber = this.ts.getAgArch().getCycleNumber();
			
			StringBuilder sb = new StringBuilder();
			intentions.forEach( i -> { sb.append( i.toString() + "\n\n" ); } );
	
			
			if( agentStatsMBeanInfo == null )
			{
				agentStatsMBean = new AgentStats();
				agentStatsMBean.setCurrentCycle( cycleNumber );
				agentStatsMBean.setIntentions(sb.toString());
				mbs.registerMBean(agentStatsMBean, agentStatsMBeanName);
			}
			else
			{
				
				MBeanAttributeInfo[] attrs = agentStatsMBeanInfo.getAttributes();
				
				logger.info( "Attributes: " );
				for( MBeanAttributeInfo attrInfo : attrs )
				{
					Object attrExisting = mbs.getAttribute( agentStatsMBeanName, attrInfo.getName() );
					
					// logger.info( "[existing] -> [attribute] " + attrInfo.getName() +  " [type] " + attrInfo.getType() + " [value] " + attrExisting.toString() );
					
				}
				
				Attribute cycleNumAttrNew = new Attribute("CurrentCycle", cycleNumber);
				
				logger.info( "[updated] -> [attribute] " + cycleNumAttrNew.getName() + " [value] " + cycleNumAttrNew.getValue());				

				mbs.setAttribute( agentStatsMBeanName, cycleNumAttrNew );
			
				Attribute intentionsNew = new Attribute( "Intentions", sb.toString());
				mbs.setAttribute( agentStatsMBeanName, intentionsNew );
				
				
			}
		
			boolean proceed = false;
			while( !proceed )
			{
				// block here until proceed is true
				try
				{
					Thread.sleep( 1500 );
				}
				catch( InterruptedException ie )
				{}	
				
				proceed = (boolean)mbs.getAttribute( agentStatsMBeanName, "Proceed" );
				mbs.setAttribute( agentStatsMBeanName, new Attribute( "Proceed", false) );
			}
			
			logger.info(  "moving on..." );
		}
		catch( Exception e )
		{
			e.printStackTrace();
		}
		
		
		
		return super.selectIntention( intentions );
	}
}

AgentStatsMBean.java (the MBean interface)

package mbean;

public interface AgentStatsMBean
{
	public int getCurrentCycle();
	public void setCurrentCycle(int cycleNum);
	
	public String getIntentions();
	public void setIntentions(String intentions);
	
	public boolean isProceed();
	public void setProceed(boolean proceed);
	
	// operations
	
	public void doProceed();
	public void sayHello();	
	public int add(int x, int y);
	
}

AgentStats.java (MBean implementation)

package mbean;

import java.util.logging.Logger;

public class AgentStats implements AgentStatsMBean
{	
	private Logger logger = Logger.getLogger( AgentStats.class.getName() );
	
	private int currentCycle;
	private String intentions;
	private boolean proceed;
	
	@Override
	public int getCurrentCycle()
	{
		return this.currentCycle;
	}
	
	@Override
	public void setCurrentCycle( int cycleNum )
	{
		this.currentCycle = cycleNum;
	}

	@Override
	public String getIntentions()
	{
		return this.intentions;
	}

	@Override
	public void setIntentions( String intentions )
	{
		this.intentions = intentions;
	}

	public boolean isProceed()
	{
		return proceed;
	}

	@Override
	public void setProceed( boolean proceed )
	{
		this.proceed = proceed;
	}
	
	/* operations */
	
	public void doProceed()
	{
		this.proceed = true;
	}
	
	@Override
	public int add( int x, int y )
	{
		return (x+y);
	}
	
	@Override
	public void sayHello()
	{
		logger.warning(  "Hello, from AgentStats MBean!!!" );
	}
	
}

[jomifred]

Thanks for sharing your progress on this. Indeed, JMX is a nice approach, specially in the Java world.

One aspect to discuss could be to implement this feature as an Agent Architecture instead of an Agent. In Jason, these two classes can be customised. The first represent the "body" of the agent: it provides interaction with the environment, with other agents, and execution power :-) -- a thread usually. The latter represent the "mind": beliefs, decisions, reasoning, ...

So it seems more natural, for me, that suspending an agent is implemented in the architecture. There are candidate methods there to place the "wait".

[mindcrime]

Thanks Jomi. I had thought that that might be the case, but I haven't gotten as far as customizing the AgentArch yet. Probably sometime this week I will explore that path.