| /* |
| * Copyright (c) 1996, 2001, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code 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 |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| package sun.rmi.transport; |
| |
| import java.lang.ref.*; |
| import sun.rmi.runtime.Log; |
| |
| /** |
| * WeakRef objects are used by the RMI runtime to hold potentially weak |
| * references to exported remote objects in the local object table. |
| * |
| * This class extends the functionality of java.lang.ref.WeakReference in |
| * several ways. The methods pin() and unpin() can be used to set |
| * whether the contained reference is strong or weak (it is weak upon |
| * construction). The hashCode() and equals() methods are overridden so |
| * that WeakRef objects hash and compare to each other according to the |
| * object identity of their referents. |
| * |
| * @author Ann Wollrath |
| * @author Peter Jones |
| */ |
| class WeakRef extends WeakReference<Object> { |
| |
| /** value of the referent's "identity" hash code */ |
| private int hashValue; |
| |
| /** strong reference to the referent, for when this WeakRef is "pinned" */ |
| private Object strongRef = null; |
| |
| /** |
| * Create a new WeakRef to the given object. |
| */ |
| public WeakRef(Object obj) { |
| super(obj); |
| setHashValue(obj); // cache object's "identity" hash code |
| } |
| |
| /** |
| * Create a new WeakRef to the given object, registered with a queue. |
| */ |
| public WeakRef(Object obj, ReferenceQueue<Object> q) { |
| super(obj, q); |
| setHashValue(obj); // cache object's "identity" hash code |
| } |
| |
| /** |
| * Pin the contained reference (make this a strong reference). |
| */ |
| public synchronized void pin() { |
| if (strongRef == null) { |
| strongRef = get(); |
| |
| if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) { |
| DGCImpl.dgcLog.log(Log.VERBOSE, |
| "strongRef = " + strongRef); |
| } |
| } |
| } |
| |
| /** |
| * Unpin the contained reference (make this a weak reference). |
| */ |
| public synchronized void unpin() { |
| if (strongRef != null) { |
| if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) { |
| DGCImpl.dgcLog.log(Log.VERBOSE, |
| "strongRef = " + strongRef); |
| } |
| |
| strongRef = null; |
| } |
| } |
| |
| /* |
| * Cache referent's "identity" hash code (so that we still have the |
| * value after the referent gets cleared). |
| * |
| * We cannot use the value from the object's hashCode() method, since |
| * if the object is of a remote class not extended from RemoteObject |
| * and it is trying to implement hashCode() and equals() so that it |
| * can be compared to stub objects, its own hash code could not have |
| * been initialized yet (see bugid 4102938). Also, object table keys |
| * based on server objects are indeed matched on object identity, so |
| * this is the correct hash technique regardless. |
| */ |
| private void setHashValue(Object obj) { |
| if (obj != null) { |
| hashValue = System.identityHashCode(obj); |
| } else { |
| hashValue = 0; |
| } |
| } |
| |
| /** |
| * Always return the "identity" hash code of the original referent. |
| */ |
| public int hashCode() { |
| return hashValue; |
| } |
| |
| /** |
| * Return true if "obj" is this identical WeakRef object, or, if the |
| * contained reference has not been cleared, if "obj" is another WeakRef |
| * object with the identical non-null referent. Otherwise, return false. |
| */ |
| public boolean equals(Object obj) { |
| if (obj instanceof WeakRef) { |
| if (obj == this) |
| return true; |
| |
| Object referent = get(); |
| return (referent != null) && (referent == ((WeakRef) obj).get()); |
| } else { |
| return false; |
| } |
| } |
| } |