| /* |
| * Copyright (c) 2003, 2008, 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.server; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.SoftReference; |
| import java.util.Map; |
| import java.util.WeakHashMap; |
| |
| /** |
| * Abstract class that maps Class objects to lazily-computed values of |
| * type V. A concrete subclass must implement the computeValue method |
| * to determine how the values are computed. |
| * |
| * The keys are only weakly reachable through this map, so this map |
| * does not prevent a class (along with its class loader, etc.) from |
| * being garbage collected if it is not otherwise strongly reachable. |
| * The values are only softly reachable through this map, so that the |
| * computed values generally persist while not otherwise strongly |
| * reachable, but their storage may be reclaimed if necessary. Also, |
| * note that if a key is strongly reachable from a value, then the key |
| * is effectively softly reachable through this map, which may delay |
| * garbage collection of classes (see 4429536). |
| **/ |
| public abstract class WeakClassHashMap<V> { |
| |
| private Map<Class<?>,ValueCell<V>> internalMap = new WeakHashMap<>(); |
| |
| protected WeakClassHashMap() { } |
| |
| public V get(Class<?> remoteClass) { |
| /* |
| * Use a mutable cell (a one-element list) to hold the soft |
| * reference to a value, to allow the lazy value computation |
| * to be synchronized with entry-level granularity instead of |
| * by locking the whole table. |
| */ |
| ValueCell<V> valueCell; |
| synchronized (internalMap) { |
| valueCell = internalMap.get(remoteClass); |
| if (valueCell == null) { |
| valueCell = new ValueCell<V>(); |
| internalMap.put(remoteClass, valueCell); |
| } |
| } |
| synchronized (valueCell) { |
| V value = null; |
| if (valueCell.ref != null) { |
| value = valueCell.ref.get(); |
| } |
| if (value == null) { |
| value = computeValue(remoteClass); |
| valueCell.ref = new SoftReference<V>(value); |
| } |
| return value; |
| } |
| } |
| |
| protected abstract V computeValue(Class<?> remoteClass); |
| |
| private static class ValueCell<T> { |
| Reference<T> ref = null; |
| ValueCell() { } |
| } |
| } |