IdManager must provide:
*
*
* public ObjectId getObjectId (Object theObject);
* public ObjectId get (long id);
* public ObjectId readObjectId (ByteBuffer bb);
* public ReferenceTypeId getReferenceTypeId (Class clazz);
* public ReferenceTypeId getReferenceType (long id);
* public ReferenceTypeId readReferenceTypeId (ByteBuffer bb);
*
*
* See the javadoc on these methods later in this file for more
* information on these functions.
*
* NOTE: All IDs handled by the ID manager (all object and reference
* type IDs) are assumed to be of type long.
*
* NOTE: This class does not manage virtual machine-specific types,
* like methods, fields, and frames. These already have unique IDs within
* the virtual machine and do not need further abstraction here.
*
* @author Keith Seitz (keiths@redhat.com)
*/
public class VMIdManager
{
// This factory generates ids for objects and types that may
// be sent to a debugger.
private static class IdFactory
{
// ID of last object / referencetype
private static Object _idLock = new Object ();
private static Object _ridLock = new Object ();
private static long _lastId = 0;
private static long _lastRid = 0;
// A list of all ID types
private static HashMap _idList = new HashMap ();
// Initialize the id list with known types
static
{
// ObjectId and ArrayId are special cases. See newObjectId.
_idList.put (ClassLoaderId.typeClass, ClassLoaderId.class);
_idList.put (ClassObjectId.typeClass, ClassObjectId.class);
_idList.put (StringId.typeClass, StringId.class);
_idList.put (ThreadId.typeClass, ThreadId.class);
_idList.put (ThreadGroupId.typeClass, ThreadGroupId.class);
}
/**
* Returns a new id for the given object
*
* @param obj SoftReference of the object for which an id is desired
* @returns a suitable object id
*/
public static ObjectId newObjectId (SoftReference obj)
{
ObjectId id = null;
Object object = obj.get ();
// Special case: arrays
if (object.getClass ().isArray ())
id = new ArrayId ();
else
{
// Loop through all classes until we hit baseclass
Class myClass;
for (myClass = object.getClass (); myClass != null;
myClass = myClass.getSuperclass ())
{
Class clz = (Class) _idList.get (myClass);
if (clz != null)
{
try
{
id = (ObjectId) clz.newInstance ();
synchronized (_idLock)
{
id.setId (++_lastId);
}
id.setReference (obj);
return id;
}
catch (InstantiationException ie)
{
// This really should not happen
throw new RuntimeException ("cannot create new ID", ie);
}
catch (IllegalAccessException iae)
{
// This really should not happen
throw new RuntimeException ("illegal access of ID", iae);
}
}
}
/* getSuperclass returned null and no matching ID type found.
So it must derive from Object. */
id = new ObjectId ();
}
synchronized (_idLock)
{
id.setId (++_lastId);
}
id.setReference (obj);
return id;
}
/**
* Returns a new reference type id for the given class
*
* @param ref SoftReference to the desired type
* @returns a suitable reference type id or null when the
* reference is cleared.
*/
public static ReferenceTypeId newReferenceTypeId (SoftReference ref)
{
ReferenceTypeId id;
Class clazz = (Class) ref.get ();
if (clazz == null)
return null;
if (clazz.isArray ())
id = new ArrayReferenceTypeId ();
else if (clazz.isInterface ())
id = new InterfaceReferenceTypeId ();
else
id = new ClassReferenceTypeId ();
id.setReference (ref);
synchronized (_ridLock)
{
id.setId (++_lastRid);
}
return id;
}
}
/**
* This class is a SoftReferenceIdentity type that is used by
* the ID manager.
*/
class ReferenceKey extends SoftReference
{
// Hash code of referent
private int _hash;
/**
* Constructs a new ReferenceKey object
* with the given referent.
*
* This constructor should only be used for object lookups
* by the backend.
*
* @param referent the object to reference
*/
public ReferenceKey (Object referent)
{
super (referent);
_hash = referent.hashCode ();
}
/**
* Constructs a new ReferenceKey object
* with the given referent and reference queue.
*
*
The JDWP back-end stores a ReferenceKey
* with its corresponding JdwpId. This constructor
* is used by the back-end when adding new IDs to be managed.
*
* @param referent the object to reference
* @param queue the queue to which to report garbage collections
*/
public ReferenceKey (Object referent, ReferenceQueue queue)
{
super (referent, queue);
_hash = referent.hashCode ();
}
/**
* Returns the hash code of the referent.
* This seems hacky, but is required in order to use this class
* as a hash table key.
*
* @returns the hash code of the referent
*/
public int hashCode ()
{
return _hash;
}
/**
* Comparator for keys
*
* This method can be used in two ways:
*
*
IdManager
private VMIdManager ()
{
_refQueue = new ReferenceQueue ();
_oidTable = new Hashtable (50);
_idTable = new Hashtable (50);
_classTable = new Hashtable (20);
_ridTable = new Hashtable (20);
}
// Updates the object ID table, removing IDs whose objects have
// been garbage collected.
private void _update ()
{
Reference ref;
while ((ref = _refQueue.poll ()) != null)
{
ObjectId id = (ObjectId) _oidTable.get (ref);
_oidTable.remove (ref);
_idTable.remove (new Long (id.getId ()));
}
}
/**
* Returns an id for the given object, adding it
* if it does not have an id.
*
* @param theObject the object to get an ID/add
* @returns the ID of the object
*/
public ObjectId getObjectId (Object theObject)
{
// Special case: null object.
if (theObject == null)
return new NullObjectId ();
ReferenceKey ref = new ReferenceKey (theObject, _refQueue);
ObjectId id = (ObjectId) _oidTable.get (ref);
if (id == null)
{
// update the tables -- this is an arbitrary place to put this
_update ();
// Object not found. Make new id for it
id = IdFactory.newObjectId (ref);
_oidTable.put (ref, id);
_idTable.put (new Long (id.getId ()), id);
}
return id;
}
/**
* Returns the JdwpId for a given ID. Unlike
* getId, it throws an exception if the ID is not
* known.
*
* @param id the numerical ID of the desired JdwpId
* @throws InvalidObjectException if the ID is not found
*/
public ObjectId get (long id)
throws InvalidObjectException
{
// Special case: null object id.
if (id == 0)
return new NullObjectId ();
ObjectId oid = (ObjectId) _idTable.get (new Long (id));
if (oid == null)
throw new InvalidObjectException (id);
return oid;
}
public ObjectId readObjectId (ByteBuffer bb)
throws InvalidObjectException
{
long id = bb.getLong ();
return get (id);
}
/**
* Gets the reference type id for the given class, creating
* a new one if it does not already have an id
*
* @param clazz the class for which to get an ID
* @returns the ID of the class
*/
public ReferenceTypeId getReferenceTypeId (Class clazz)
{
ReferenceKey ref = new ReferenceKey (clazz);
ReferenceTypeId id = (ReferenceTypeId)_classTable.get (ref);
if (id == null)
{
// Object not found. Make new id for it
id = IdFactory.newReferenceTypeId (ref);
_classTable.put (ref, id);
_ridTable.put (new Long (id.getId ()), id);
}
return id;
}
/**
* Returns the ReferenceTypeId for a given ID. Unlike
* getReferenceTypeId, it throws an exception if the ID is not
* known.
*
* @param id the numerical ID of the desired reference type
* @throws InvalidClassException if the ID is not found
*/
public ReferenceTypeId getReferenceType (long id)
throws InvalidClassException
{
ReferenceTypeId rid = (ReferenceTypeId) _ridTable.get (new Long (id));
if (rid == null)
throw new InvalidClassException (id);
return rid;
}
public ReferenceTypeId readReferenceTypeId (ByteBuffer bb)
throws InvalidClassException
{
long id = bb.getLong ();
return getReferenceType (id);
}
}