Re: [RFA/JDWP] ReferenceKey

[Keith Seitz <keiths at redhat dot com>]

On Fri, 2005-06-17 at 12:25 -0700, Keith Seitz wrote:

> ChangeLog
> 2005-06-17  Keith Seitz  <keiths@redhat.com>
> 
>         * gnu/classpath/jdwp/id/ReferenceKey.java: New file.

Geez. I did it again...

Patch is attached this time. Really. It is. I promise.

Keith

Index: gnu/classpath/jdwp/id/ReferenceKey.java
===================================================================
RCS file: gnu/classpath/jdwp/id/ReferenceKey.java
diff -N gnu/classpath/jdwp/id/ReferenceKey.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gnu/classpath/jdwp/id/ReferenceKey.java	17 Jun 2005 19:24:36 -0000
@@ -0,0 +1,130 @@
+/* ReferenceKey.java -- a SoftReference key type for Jdwp IDs
+   Copyright (C) 2005 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., 59 Temple Place, Suite 330, Boston, MA
+02111-1307 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+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
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package gnu.classpath.jdwp.id;
+
+import gnu.classpath.jdwp.exception.InvalidObjectException;
+
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+
+/**
+ * This class is a softreference type that is used by
+ * the ID manager as an index into a hash table.
+ */
+public 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;
+
+	// That failed, so we're looking for a matching Object
+	Object me = get ();
+	Object other = ref.get ();
+	return (me == null ? false : me.equals (other));
+      }
+
+    return false;
+  }
+}