gcc/libjava/gnu/classpath/jdwp/VMIdManager.java

/* VMIdManager.java -- A reference/example implementation of a manager for
   JDWP object/reference type IDs

   Copyright (C) 2005, 2006 Free Software Foundation

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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permission to link this library with independent modules to produce an
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or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
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exception statement from your version. */


package gnu.classpath.jdwp;

import gnu.classpath.jdwp.exception.InvalidClassException;
import gnu.classpath.jdwp.exception.InvalidObjectException;
import gnu.classpath.jdwp.id.*;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.nio.ByteBuffer;
import java.util.HashMap;
import java.util.Hashtable;

/**
 * This class manages objects and referencetypes that are reported
 * to the debugger. All objects and referencetypes reported to the
 * debugger should go through this manager.
 *
 * A brief summary of what an <code>IdManager</code> must provide:
 *
 * <code>
 * 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);
 * </code>
 *
 * See the javadoc on these methods later in this file for more
 * information on these functions.
 *
 * <b>NOTE:</b> All IDs handled by the ID manager (all object and reference
 * type IDs) are assumed to be of type <code>long</code>.
 *
 * <b>NOTE:</b> 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 <code>ReferenceKey</code> object
     * with the given referent.
     *
     * <p>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 <code>ReferenceKey</code> object
     * with the given referent and reference queue.
     *
     * <p>The JDWP back-end stores a <code>ReferenceKey</code>
     * with its corresponding <code>JdwpId</code>. 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:
     *
     * <ol>
     *    <li>For table lookups, where we want to compare referents</li>
     *    <li>For clearing GCd objects, where we want to compare the actual
     *        key object (not the referent)</li>
     * </ol>
     */
    public boolean equals (Object obj)
    {
      if (obj instanceof ReferenceKey)
	{
	  ReferenceKey ref = (ReferenceKey) obj;
	  
	  /* First check if the two references are the same.
	     If they are, that means we must be clearing GCd objects. */
	  if (this == obj)
	    return true;
	  
	  return (ref.get () == get ());
	}
      
      return false;
    }
  }
  
  // instance of VMIdManager
  private static VMIdManager _idm = new VMIdManager ();

  // A reference queue for our objects
  private ReferenceQueue _refQueue;

  // Mapping of objects (ReferenceKey) to IDs (ObjectId)
  private Hashtable _oidTable;

  // Mapping of ID numbers (Long) to IDs (ObjectId)
  private Hashtable _idTable;

  /* Mapping of class (ReferenceKey) to IDs (ReferenceTypeId) for reference
     types. Unlike other types, reference id types are NEVER released. */
  private Hashtable _classTable;

  // Mapping of ID numbers (Long) to reference type IDs (ReferenceTypeId)
  private Hashtable _ridTable;

  /**
   * Gets the instance of VMIdManager, constructing a new one
   * if none currently exists.
   */
  public static VMIdManager getDefault ()
  {
    return _idm;
  }

  // Constructs a new <code>IdManager</code>
  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)
  {
    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 <code>JdwpId</code> for a given ID. Unlike
   * <code>getId</code>, it throws an exception if the ID is not
   * known.
   *
   * @param id  the numerical ID of the desired <code>JdwpId</code>
   * @throws InvalidObjectException if the ID is not found
   */
  public ObjectId get (long id)
    throws InvalidObjectException
  {
    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 <code>ReferenceTypeId</code> for a given ID. Unlike
   * <code>getReferenceTypeId</code>, 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);
  }
}