--- a/jdk/src/java.base/share/classes/java/lang/reflect/WeakCache.java Sun Apr 10 08:41:00 2016 -0700
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,381 +0,0 @@
-/*
- * Copyright (c) 2013, 2014, 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 java.lang.reflect;
-
-import java.lang.ref.ReferenceQueue;
-import java.lang.ref.WeakReference;
-import java.util.Objects;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-import java.util.function.BiFunction;
-import java.util.function.Supplier;
-
-/**
- * Cache mapping pairs of {@code (key, sub-key) -> value}. Keys and values are
- * weakly but sub-keys are strongly referenced. Keys are passed directly to
- * {@link #get} method which also takes a {@code parameter}. Sub-keys are
- * calculated from keys and parameters using the {@code subKeyFactory} function
- * passed to the constructor. Values are calculated from keys and parameters
- * using the {@code valueFactory} function passed to the constructor.
- * Keys can be {@code null} and are compared by identity while sub-keys returned by
- * {@code subKeyFactory} or values returned by {@code valueFactory}
- * can not be null. Sub-keys are compared using their {@link #equals} method.
- * Entries are expunged from cache lazily on each invocation to {@link #get},
- * {@link #containsValue} or {@link #size} methods when the WeakReferences to
- * keys are cleared. Cleared WeakReferences to individual values don't cause
- * expunging, but such entries are logically treated as non-existent and
- * trigger re-evaluation of {@code valueFactory} on request for their
- * key/subKey.
- *
- * @author Peter Levart
- * @param <K> type of keys
- * @param <P> type of parameters
- * @param <V> type of values
- */
-final class WeakCache<K, P, V> {
-
- private final ReferenceQueue<K> refQueue
- = new ReferenceQueue<>();
- // the key type is Object for supporting null key
- private final ConcurrentMap<Object, ConcurrentMap<Object, Supplier<V>>> map
- = new ConcurrentHashMap<>();
- private final ConcurrentMap<Supplier<V>, Boolean> reverseMap
- = new ConcurrentHashMap<>();
- private final BiFunction<K, P, ?> subKeyFactory;
- private final BiFunction<K, P, V> valueFactory;
-
- /**
- * Construct an instance of {@code WeakCache}
- *
- * @param subKeyFactory a function mapping a pair of
- * {@code (key, parameter) -> sub-key}
- * @param valueFactory a function mapping a pair of
- * {@code (key, parameter) -> value}
- * @throws NullPointerException if {@code subKeyFactory} or
- * {@code valueFactory} is null.
- */
- public WeakCache(BiFunction<K, P, ?> subKeyFactory,
- BiFunction<K, P, V> valueFactory) {
- this.subKeyFactory = Objects.requireNonNull(subKeyFactory);
- this.valueFactory = Objects.requireNonNull(valueFactory);
- }
-
- /**
- * Look-up the value through the cache. This always evaluates the
- * {@code subKeyFactory} function and optionally evaluates
- * {@code valueFactory} function if there is no entry in the cache for given
- * pair of (key, subKey) or the entry has already been cleared.
- *
- * @param key possibly null key
- * @param parameter parameter used together with key to create sub-key and
- * value (should not be null)
- * @return the cached value (never null)
- * @throws NullPointerException if {@code parameter} passed in or
- * {@code sub-key} calculated by
- * {@code subKeyFactory} or {@code value}
- * calculated by {@code valueFactory} is null.
- */
- public V get(K key, P parameter) {
- Objects.requireNonNull(parameter);
-
- expungeStaleEntries();
-
- Object cacheKey = CacheKey.valueOf(key, refQueue);
-
- // lazily install the 2nd level valuesMap for the particular cacheKey
- ConcurrentMap<Object, Supplier<V>> valuesMap = map.get(cacheKey);
- if (valuesMap == null) {
- ConcurrentMap<Object, Supplier<V>> oldValuesMap
- = map.putIfAbsent(cacheKey,
- valuesMap = new ConcurrentHashMap<>());
- if (oldValuesMap != null) {
- valuesMap = oldValuesMap;
- }
- }
-
- // create subKey and retrieve the possible Supplier<V> stored by that
- // subKey from valuesMap
- Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
- Supplier<V> supplier = valuesMap.get(subKey);
- Factory factory = null;
-
- while (true) {
- if (supplier != null) {
- // supplier might be a Factory or a CacheValue<V> instance
- V value = supplier.get();
- if (value != null) {
- return value;
- }
- }
- // else no supplier in cache
- // or a supplier that returned null (could be a cleared CacheValue
- // or a Factory that wasn't successful in installing the CacheValue)
-
- // lazily construct a Factory
- if (factory == null) {
- factory = new Factory(key, parameter, subKey, valuesMap);
- }
-
- if (supplier == null) {
- supplier = valuesMap.putIfAbsent(subKey, factory);
- if (supplier == null) {
- // successfully installed Factory
- supplier = factory;
- }
- // else retry with winning supplier
- } else {
- if (valuesMap.replace(subKey, supplier, factory)) {
- // successfully replaced
- // cleared CacheEntry / unsuccessful Factory
- // with our Factory
- supplier = factory;
- } else {
- // retry with current supplier
- supplier = valuesMap.get(subKey);
- }
- }
- }
- }
-
- /**
- * Checks whether the specified non-null value is already present in this
- * {@code WeakCache}. The check is made using identity comparison regardless
- * of whether value's class overrides {@link Object#equals} or not.
- *
- * @param value the non-null value to check
- * @return true if given {@code value} is already cached
- * @throws NullPointerException if value is null
- */
- public boolean containsValue(V value) {
- Objects.requireNonNull(value);
-
- expungeStaleEntries();
- return reverseMap.containsKey(new LookupValue<>(value));
- }
-
- /**
- * Returns the current number of cached entries that
- * can decrease over time when keys/values are GC-ed.
- */
- public int size() {
- expungeStaleEntries();
- return reverseMap.size();
- }
-
- @SuppressWarnings("unchecked") // refQueue.poll actually returns CacheKey<K>
- private void expungeStaleEntries() {
- CacheKey<K> cacheKey;
- while ((cacheKey = (CacheKey<K>)refQueue.poll()) != null) {
- cacheKey.expungeFrom(map, reverseMap);
- }
- }
-
- /**
- * A factory {@link Supplier} that implements the lazy synchronized
- * construction of the value and installment of it into the cache.
- */
- private final class Factory implements Supplier<V> {
-
- private final K key;
- private final P parameter;
- private final Object subKey;
- private final ConcurrentMap<Object, Supplier<V>> valuesMap;
-
- Factory(K key, P parameter, Object subKey,
- ConcurrentMap<Object, Supplier<V>> valuesMap) {
- this.key = key;
- this.parameter = parameter;
- this.subKey = subKey;
- this.valuesMap = valuesMap;
- }
-
- @Override
- public synchronized V get() { // serialize access
- // re-check
- Supplier<V> supplier = valuesMap.get(subKey);
- if (supplier != this) {
- // something changed while we were waiting:
- // might be that we were replaced by a CacheValue
- // or were removed because of failure ->
- // return null to signal WeakCache.get() to retry
- // the loop
- return null;
- }
- // else still us (supplier == this)
-
- // create new value
- V value = null;
- try {
- value = Objects.requireNonNull(valueFactory.apply(key, parameter));
- } finally {
- if (value == null) { // remove us on failure
- valuesMap.remove(subKey, this);
- }
- }
- // the only path to reach here is with non-null value
- assert value != null;
-
- // wrap value with CacheValue (WeakReference)
- CacheValue<V> cacheValue = new CacheValue<>(value);
-
- // try replacing us with CacheValue (this should always succeed)
- if (valuesMap.replace(subKey, this, cacheValue)) {
- // put also in reverseMap
- reverseMap.put(cacheValue, Boolean.TRUE);
- } else {
- throw new AssertionError("Should not reach here");
- }
-
- // successfully replaced us with new CacheValue -> return the value
- // wrapped by it
- return value;
- }
- }
-
- /**
- * Common type of value suppliers that are holding a referent.
- * The {@link #equals} and {@link #hashCode} of implementations is defined
- * to compare the referent by identity.
- */
- private interface Value<V> extends Supplier<V> {}
-
- /**
- * An optimized {@link Value} used to look-up the value in
- * {@link WeakCache#containsValue} method so that we are not
- * constructing the whole {@link CacheValue} just to look-up the referent.
- */
- private static final class LookupValue<V> implements Value<V> {
- private final V value;
-
- LookupValue(V value) {
- this.value = value;
- }
-
- @Override
- public V get() {
- return value;
- }
-
- @Override
- public int hashCode() {
- return System.identityHashCode(value); // compare by identity
- }
-
- @Override
- public boolean equals(Object obj) {
- return obj == this ||
- obj instanceof Value &&
- this.value == ((Value<?>) obj).get(); // compare by identity
- }
- }
-
- /**
- * A {@link Value} that weakly references the referent.
- */
- private static final class CacheValue<V>
- extends WeakReference<V> implements Value<V>
- {
- private final int hash;
-
- CacheValue(V value) {
- super(value);
- this.hash = System.identityHashCode(value); // compare by identity
- }
-
- @Override
- public int hashCode() {
- return hash;
- }
-
- @Override
- public boolean equals(Object obj) {
- V value;
- return obj == this ||
- obj instanceof Value &&
- // cleared CacheValue is only equal to itself
- (value = get()) != null &&
- value == ((Value<?>) obj).get(); // compare by identity
- }
- }
-
- /**
- * CacheKey containing a weakly referenced {@code key}. It registers
- * itself with the {@code refQueue} so that it can be used to expunge
- * the entry when the {@link WeakReference} is cleared.
- */
- private static final class CacheKey<K> extends WeakReference<K> {
-
- // a replacement for null keys
- private static final Object NULL_KEY = new Object();
-
- static <K> Object valueOf(K key, ReferenceQueue<K> refQueue) {
- return key == null
- // null key means we can't weakly reference it,
- // so we use a NULL_KEY singleton as cache key
- ? NULL_KEY
- // non-null key requires wrapping with a WeakReference
- : new CacheKey<>(key, refQueue);
- }
-
- private final int hash;
-
- private CacheKey(K key, ReferenceQueue<K> refQueue) {
- super(key, refQueue);
- this.hash = System.identityHashCode(key); // compare by identity
- }
-
- @Override
- public int hashCode() {
- return hash;
- }
-
- @Override
- @SuppressWarnings("unchecked")
- public boolean equals(Object obj) {
- K key;
- return obj == this ||
- obj != null &&
- obj.getClass() == this.getClass() &&
- // cleared CacheKey is only equal to itself
- (key = this.get()) != null &&
- // compare key by identity
- key == ((CacheKey<K>) obj).get(); // Cast is safe from getClass check
- }
-
- void expungeFrom(ConcurrentMap<?, ? extends ConcurrentMap<?, ?>> map,
- ConcurrentMap<?, Boolean> reverseMap) {
- // removing just by key is always safe here because after a CacheKey
- // is cleared and enqueue-ed it is only equal to itself
- // (see equals method)...
- ConcurrentMap<?, ?> valuesMap = map.remove(this);
- // remove also from reverseMap if needed
- if (valuesMap != null) {
- for (Object cacheValue : valuesMap.values()) {
- reverseMap.remove(cacheValue);
- }
- }
- }
- }
-}