88 lines
2.9 KiB
Java
88 lines
2.9 KiB
Java
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/*
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* Copyright (c) 2021, 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 java.io;
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import java.lang.ref.Reference;
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import java.lang.ref.ReferenceQueue;
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import java.lang.ref.SoftReference;
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// Maps Class instances to values of type T. Under memory pressure, the
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// mapping is released (under soft references GC policy) and would be
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// recomputed the next time it is queried. The mapping is bound to the
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// lifetime of the class: when the class is unloaded, the mapping is
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// removed too.
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abstract class ClassCache<T> {
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private static class CacheRef<T> extends SoftReference<T> {
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private final Class<?> type;
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CacheRef(T referent, ReferenceQueue<T> queue, Class<?> type) {
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super(referent, queue);
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this.type = type;
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}
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Class<?> getType() {
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return type;
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}
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}
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private final ReferenceQueue<T> queue;
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private final ClassValue<SoftReference<T>> map;
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protected abstract T computeValue(Class<?> cl);
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protected ClassCache() {
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queue = new ReferenceQueue<>();
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map = new ClassValue<>() {
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@Override
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protected SoftReference<T> computeValue(Class<?> type) {
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return new CacheRef<>(ClassCache.this.computeValue(type), queue, type);
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}
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};
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}
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T get(Class<?> cl) {
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processQueue();
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T val;
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do {
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SoftReference<T> ref = map.get(cl);
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val = ref.get();
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if (val == null) {
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map.remove(cl);
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}
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} while (val == null);
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return val;
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}
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private void processQueue() {
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Reference<? extends T> ref;
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while((ref = queue.poll()) != null) {
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CacheRef<? extends T> cacheRef = (CacheRef<? extends T>)ref;
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map.remove(cacheRef.getType());
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}
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}
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}
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