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Jadex Rules is a small lightweight rule engine, which currently employs the well-known Rete algorithm for highly efficient rule matching. Jadex rules is therefore similar to other rule engines like JESS and Drools. Despite the similarities there are also important differences between these systems: * Jadex Rules is very small and intended to be used as component of other software. Even though rules can be specified in a Java dialect as well as (a small variation of) the CLIPS language its primary usage is on the API level. Jadex Rules is currently the core component of the Jadex BDI reasoning engine. * Jadex Rules cleanly separates between state and rule representation. This allows the state implementation as well as the matcher to be flexibly exchanged. Some experiments have e.g. been conducted with a Jena representation. Regarding the matcher, it is planned to support also the Treat algorithm, which has a lower memory footprint than Rete. * Jadex Rules pays close attention to rule debugging. The state as well as the rete engine can be observed at runtime. The rule debugger provides functionalities to execute a rule program stepwise and also use rule breakpoints to stop the execution at those points.

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package jadex.rules.state.javaimpl;

import jadex.rules.state.OAVAttributeType;
import jadex.rules.state.OAVTypeModel;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;

/**
 *  An object holding the state as
 *  OAV triples (object, attribute, value).
 */
public class OAVState	extends OAVAbstractState
{
	//-------- attributes --------
	
	/** The objects table (oid -> content map). */
	protected Map objects;
	
	/**  Writing (and therefore resurrecting) is not supported. */
	protected Map externalusages;
	
	//-------- constructors --------
	
	/**
	 *  Create a new empty OAV state representation.
	 */
	public OAVState(OAVTypeModel tmodel)
	{
		super(tmodel);
		this.objects = new LinkedHashMap();
		this.externalusages = new LinkedHashMap();
	}
	
	//-------- object management --------
		
	/**
	 *  Add an external usage of a state object (oid). This prevents
	 *  the oav object of being garbage collected as long
	 *  as external references are present.
	 *  @param id The oav object id.
	 *  @param external The user object.
	 */
	public void addExternalObjectUsage(Object id, Object external)
	{
		// #ifndef MIDP
		assert nocheck || generator.isId(id);
		// #endif

		// Get the usages of the oav object
		Integer cnt = (Integer)externalusages.get(id);
		if(cnt==null)
			cnt = new Integer(1);
		else
			cnt = new Integer(cnt.intValue()+1);
		externalusages.put(id, cnt);
		
//		if(id.toString().indexOf("waitabstraction")!=-1)
//		{
//			System.err.println("Add ex: "+id/*+" "+external*/+" "+cnt);
//			Thread.dumpStack();
//		}
	}
	
	/**
	 *  Remove an external usage of a state object (oid). This allows
	 *  the oav object of being garbage collected when no
	 *  further external references and no internal references
	 *  are present.
	 *  @param id The oav object id.
	 *  @param external The state external object.
	 */
	public void removeExternalObjectUsage(Object id, Object external)
	{
		// #ifndef MIDP
		assert nocheck || generator.isId(id);
		// #endif

		Integer cnt = (Integer)externalusages.get(id);
		if(cnt==null)
			throw new RuntimeException("Reference not found: "+id);
	
//		if(id.toString().indexOf("plan_5")!=-1)
//			System.err.println("Remove ex: "+id/*+" "+external*/+" "+cnt);

		if(cnt.intValue()==1)
		{
			externalusages.remove(id);

			// Delete object, when there are no internal references.
			Map	iusages	= getObjectUsages(id);
//			if(objects.containsKey(id) && !rootobjects.contains(id) && (iusages==null || iusages.isEmpty()))
			if(internalContainsObject(id) && !rootobjects.contains(id) && (iusages==null || iusages.isEmpty()))
			{
//					System.err.println("Garbage collecting unreferenced object: "+id);
//					Thread.dumpStack();
				
				// Remove pseudo external references from contained objects, when original object once was referenced
				if(iusages!=null)
				{
//					Map	content	= (Map)objects.get(id);
					Map	content	= internalGetObjectContent(id);
					for(Iterator it=content.keySet().iterator(); it.hasNext(); )
					{
						OAVAttributeType attribute = (OAVAttributeType)it.next();
						Object value = content.get(attribute);
						if(value!=null)
						{
							if(attribute.getMultiplicity().equals(OAVAttributeType.NONE))
							{
								if(generator.isId(value) && isManaged(value))
									removeExternalObjectUsage(value, this);
							}
							else
							{
								if(value instanceof Map)
								{
									Map	values	= (Map)value;
									for(Iterator vit = values.keySet().iterator(); vit.hasNext();)
									{
										Object key = vit.next();
										Object	value1	= values.get(key);
										if(generator.isId(key) && isManaged(key))
											removeExternalObjectUsage(key, this);
										if(generator.isId(value1) && isManaged(value1))
											removeExternalObjectUsage(value1, this);
									}
								}
								else
								{
									for(Iterator vit = ((Collection)value).iterator(); vit.hasNext();)
									{
										Object value1 = vit.next();
										if(generator.isId(value1) && isManaged(value1))
											removeExternalObjectUsage(value1, this);
									}
								}
							}
						}
					}
					removeObject(id);
				}
				
				// Remove object as if it was a normal reference
				else
				{
					internalDropObject(id, null, false);
				}

//					System.err.println("Garbage collected unreferenced object: "+id);
			}
		}
		else
		{
			externalusages.put(id, new Integer(cnt.intValue()-1));
		}
	}
	
	/**
	 *  Test if an object is externally used.
	 *  @return True, if externally used.
	 */
	protected boolean isExternallyUsed(Object id)
	{
		return externalusages.get(id)!=null;
	}
	
	//-------- internal object handling --------
	
	/**
	 *  Internally create an object.
	 *  @param id The id.
	 *  @return The content map of the new object.
	 */
	protected Map internalCreateObject(Object id)
	{
		Map content = new LinkedHashMap();
		objects.put(id, content);
		return content;
	}
	
	/**
	 *  Remove an object from the state objects.
	 *  @param id The id.
	 *  @return The content map of the object.
	 */
	protected Map internalRemoveObject(Object id)
	{
		return (Map)objects.remove(id);
	}
	
	/**
	 *  Get the object content of an object.
	 *  @param id The id.
	 *  @return The content map of the object.
	 */
	protected Map internalGetObjectContent(Object id)
	{
		return (Map)objects.get(id);
	}
	
	/**
	 *  Test if an object is contained in the state.
	 *  @param id The id.
	 *  @return True, if object is contained.
	 */
	protected boolean internalContainsObject(Object id)
	{
		return objects.containsKey(id);
	}
	
	/**
	 *  Test how many object are contained in the state.
	 *  @return The number of objects.
	 */
	protected int internalObjectsSize()
	{
		return objects.size();
	}
	
	/**
	 *  Get a set of the internal state objects.
	 *  @return A set of the state objects. 
	 */
	protected Set internalGetObjects()
	{
		return objects.keySet();
	}

}