jadex.rules.state.javaimpl.OAVWeakIdGenerator Maven / Gradle / Ivy
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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.
package jadex.rules.state.javaimpl;
// #ifndef MIDP
import jadex.commons.collection.WeakEntry;
import jadex.rules.state.IOAVState;
import jadex.rules.state.OAVObjectType;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;
/**
* Id generator using easy to read names and numbers.
*/
public class OAVWeakIdGenerator implements IOAVIdGenerator
{
//-------- attributes --------
/** The id counter map (type -> count). */
protected Map counters;
/** The reference queue for stale external ids. */
protected ReferenceQueue queue;
//-------- constructors --------
/**
* Create a new id generator.
*/
public OAVWeakIdGenerator(ReferenceQueue queue)
{
this.counters = new HashMap();
this.queue = queue;
}
/**
* Create a unique id.
* @param state The state.
* @param type The object type.
* @return The new id.
*/
public Object createId(IOAVState state, OAVObjectType type)
{
long start = 1;
if(counters.containsKey(type))
{
start = ((Long)counters.get(type)).longValue();
}
long id = start;
OAVInternalObjectId ret = new OAVInternalObjectId(type, id++, queue);
if(state.containsObject(ret))
System.out.println("Warning, id overflow.");
while(state.containsObject(ret) && id!=start)
{
ret = new OAVInternalObjectId(type, id++, queue);
}
if(state.containsObject(ret))
throw new RuntimeException("No free id available.");
counters.put(type, new Long(id));
// System.out.println("generated: "+ret);
return ret;
}
/**
* Test if an object is an id.
* @param state The state.
* @param type The object type.
* @return The new id.
*/
public boolean isId(Object id)
{
return id!=null && (id instanceof OAVInternalObjectId || id instanceof OAVExternalObjectId);
}
//-------- helper classes --------
/**
* An id for an OAV object.
*/
public static class OAVInternalObjectId
{
//-------- attributes --------
/** The object type. */
protected OAVObjectType type;
/** The id value. */
protected long id;
/** The weak reference to the external id. */
protected WeakReference extid;
/** The weak reference to the phantom external id
* (e.g. used in rete memory, but doesn't prevent garbage collection). */
protected WeakReference extid2;
/** The reference queue. */
protected ReferenceQueue queue;
//-------- constructors --------
/**
* Create an OAV object id with the given id value.
* @param id The id value.
*/
OAVInternalObjectId(OAVObjectType type, long id, ReferenceQueue queue)
{
this.type = type;
this.id = id;
this.queue = queue;
}
//-------- methods --------
/**
* Get the weak external id.
*/
public OAVExternalObjectId getWeakExternalId()
{
OAVExternalObjectId ret = extid==null? null: (OAVExternalObjectId)extid.get();
if(ret==null)
{
ret = new OAVExternalObjectId(this);
extid = new WeakEntry(ret, this, queue);
}
return ret;
}
/**
* Get the phantom external id (e.g. used in events).
*/
public OAVExternalObjectId getPhantomExternalId()
{
OAVExternalObjectId ret = extid2==null? null: (OAVExternalObjectId)extid2.get();
if(ret==null)
{
ret = new OAVExternalObjectId(this);
extid2 = new WeakReference(ret);
}
return ret;
}
/**
* Test if no external references exist.
* @return True, if no exist.
*/
public boolean isClear()
{
return (extid==null? null: (OAVExternalObjectId)extid.get())==null;
}
/**
* Create a string representation of this OAV object id.
*/
public String toString()
{
return type.getName()+"_"+id;
}
/**
* Test if two object are equal.
* @param object The object to compare to.
*/
public boolean equals(Object object)
{
return object instanceof OAVInternalObjectId
&& this.id==((OAVInternalObjectId)object).id
&& this.type.equals(((OAVInternalObjectId)object).type);
}
/**
* Return the hashcode for this id.
* @return The hashcode for this id.
*/
public int hashCode()
{
int ret = 31 + (int)(id ^ (id >>> 32));
ret = 31 * ret + type.hashCode();
return ret;
}
}
/**
* An id for an OAV object.
*/
public static class OAVExternalObjectId
{
//-------- attributes --------
/** The object type. */
protected OAVInternalObjectId id;
//-------- constructors --------
/**
* Create an OAV object id with the given id value.
* @param id The id value.
*/
private OAVExternalObjectId(OAVInternalObjectId id)
{
this.id = id;
}
//-------- methods --------
/**
* Get the internal id.
*/
public OAVInternalObjectId getInternalId()
{
return id;
}
/**
* Create a string representation of this OAV object id.
*/
public String toString()
{
return "extid_"+id.toString();
}
/**
* Test if two object are equal.
* @param object The object to compare to.
*/
public boolean equals(Object object)
{
return object!=null && object.equals(id); // Order is important!
}
/**
* Return the hashcode for this id.
* @return The hashcode for this id.
*/
public int hashCode()
{
return id.hashCode();
}
}
}
// #endif