author | rehn |
Fri, 29 Nov 2019 12:09:25 +0100 | |
changeset 59325 | 3636bab5e81e |
parent 47216 | 71c04702a3d5 |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package sun.rmi.server; |
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import java.lang.ref.Reference; |
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import java.lang.ref.SoftReference; |
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import java.util.Map; |
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import java.util.WeakHashMap; |
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/** |
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* Abstract class that maps Class objects to lazily-computed values of |
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* type V. A concrete subclass must implement the computeValue method |
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* to determine how the values are computed. |
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* |
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* The keys are only weakly reachable through this map, so this map |
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* does not prevent a class (along with its class loader, etc.) from |
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* being garbage collected if it is not otherwise strongly reachable. |
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* The values are only softly reachable through this map, so that the |
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* computed values generally persist while not otherwise strongly |
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* reachable, but their storage may be reclaimed if necessary. Also, |
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* note that if a key is strongly reachable from a value, then the key |
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* is effectively softly reachable through this map, which may delay |
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* garbage collection of classes (see 4429536). |
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**/ |
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public abstract class WeakClassHashMap<V> { |
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private Map<Class<?>,ValueCell<V>> internalMap = new WeakHashMap<>(); |
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protected WeakClassHashMap() { } |
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public V get(Class<?> remoteClass) { |
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/* |
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* Use a mutable cell (a one-element list) to hold the soft |
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* reference to a value, to allow the lazy value computation |
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* to be synchronized with entry-level granularity instead of |
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* by locking the whole table. |
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*/ |
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ValueCell<V> valueCell; |
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synchronized (internalMap) { |
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valueCell = internalMap.get(remoteClass); |
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if (valueCell == null) { |
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valueCell = new ValueCell<V>(); |
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internalMap.put(remoteClass, valueCell); |
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} |
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} |
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synchronized (valueCell) { |
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V value = null; |
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if (valueCell.ref != null) { |
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value = valueCell.ref.get(); |
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} |
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if (value == null) { |
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value = computeValue(remoteClass); |
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valueCell.ref = new SoftReference<V>(value); |
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} |
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return value; |
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} |
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} |
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protected abstract V computeValue(Class<?> remoteClass); |
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private static class ValueCell<T> { |
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Reference<T> ref = null; |
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ValueCell() { } |
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} |
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} |