| /* |
| * Copyright (c) 2016, 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; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.ReferenceQueue; |
| import java.lang.ref.WeakReference; |
| import java.util.Collection; |
| import java.util.Objects; |
| import java.util.concurrent.ConcurrentHashMap; |
| import java.util.function.BiFunction; |
| |
| /** |
| * A WeakHashMap-like data structure that uses a pair of weakly-referenced keys |
| * with identity equality semantics to associate a strongly-referenced value. |
| * Unlike WeakHashMap, this data structure is thread-safe. |
| * |
| * @param <K1> the type of 1st key in key pair |
| * @param <K2> the type of 2nd key in key pair |
| * @param <V> the type of value |
| * @author Peter Levart |
| */ |
| final class WeakPairMap<K1, K2, V> { |
| |
| private final ConcurrentHashMap<Pair<K1, K2>, V> map = new ConcurrentHashMap<>(); |
| private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); |
| |
| /** |
| * Tests if the specified pair of keys are associated with a value |
| * in the WeakPairMap. |
| * |
| * @param k1 the 1st of the pair of keys |
| * @param k2 the 2nd of the pair of keys |
| * @return true if and only if the specified key pair is in this WeakPairMap, |
| * as determined by the identity comparison; false otherwise |
| * @throws NullPointerException if any of the specified keys is null |
| */ |
| public boolean containsKeyPair(K1 k1, K2 k2) { |
| expungeStaleAssociations(); |
| return map.containsKey(Pair.lookup(k1, k2)); |
| } |
| |
| /** |
| * Returns the value to which the specified pair of keys is mapped, or null |
| * if this WeakPairMap contains no mapping for the key pair. |
| * <p>More formally, if this WeakPairMap contains a mapping from a key pair |
| * {@code (_k1, _k2)} to a value {@code v} such that |
| * {@code k1 == _k1 && k2 == _k2}, then this method returns {@code v}; |
| * otherwise it returns {@code null}. |
| * (There can be at most one such mapping.) |
| * |
| * @param k1 the 1st of the pair of keys for which the mapped value is to |
| * be returned |
| * @param k2 the 2nd of the pair of keys for which the mapped value is to |
| * be returned |
| * @return the value to which the specified key pair is mapped, or null if |
| * this map contains no mapping for the key pair |
| * @throws NullPointerException if any of the specified keys is null |
| */ |
| public V get(K1 k1, K2 k2) { |
| expungeStaleAssociations(); |
| return map.get(Pair.lookup(k1, k2)); |
| } |
| |
| /** |
| * Maps the specified key pair to the specified value in this WeakPairMap. |
| * Neither the keys nor the value can be null. |
| * <p>The value can be retrieved by calling the {@link #get} method |
| * with the the same keys (compared by identity). |
| * |
| * @param k1 the 1st of the pair of keys with which the specified value is to |
| * be associated |
| * @param k2 the 2nd of the pair of keys with which the specified value is to |
| * be associated |
| * @param v value to be associated with the specified key pair |
| * @return the previous value associated with key pair, or {@code null} if |
| * there was no mapping for key pair |
| * @throws NullPointerException if any of the specified keys or value is null |
| */ |
| public V put(K1 k1, K2 k2, V v) { |
| expungeStaleAssociations(); |
| return map.put(Pair.weak(k1, k2, queue), v); |
| } |
| |
| /** |
| * If the specified key pair is not already associated with a value, |
| * associates it with the given value and returns {@code null}, else does |
| * nothing and returns the currently associated value. |
| * |
| * @param k1 the 1st of the pair of keys with which the specified value is to |
| * be associated |
| * @param k2 the 2nd of the pair of keys with which the specified value is to |
| * be associated |
| * @param v value to be associated with the specified key pair |
| * @return the previous value associated with key pair, or {@code null} if |
| * there was no mapping for key pair |
| * @throws NullPointerException if any of the specified keys or value is null |
| */ |
| public V putIfAbsent(K1 k1, K2 k2, V v) { |
| expungeStaleAssociations(); |
| return map.putIfAbsent(Pair.weak(k1, k2, queue), v); |
| } |
| |
| /** |
| * If the specified key pair is not already associated with a value, |
| * attempts to compute its value using the given mapping function |
| * and enters it into this WeakPairMap unless {@code null}. The entire |
| * method invocation is performed atomically, so the function is |
| * applied at most once per key pair. Some attempted update operations |
| * on this WeakPairMap by other threads may be blocked while computation |
| * is in progress, so the computation should be short and simple, |
| * and must not attempt to update any other mappings of this WeakPairMap. |
| * |
| * @param k1 the 1st of the pair of keys with which the |
| * computed value is to be associated |
| * @param k2 the 2nd of the pair of keys with which the |
| * computed value is to be associated |
| * @param mappingFunction the function to compute a value |
| * @return the current (existing or computed) value associated with |
| * the specified key pair, or null if the computed value is null |
| * @throws NullPointerException if any of the specified keys or |
| * mappingFunction is null |
| * @throws IllegalStateException if the computation detectably |
| * attempts a recursive update to this map |
| * that would otherwise never complete |
| * @throws RuntimeException or Error if the mappingFunction does so, in |
| * which case the mapping is left unestablished |
| */ |
| public V computeIfAbsent(K1 k1, K2 k2, |
| BiFunction<? super K1, ? super K2, ? extends V> |
| mappingFunction) { |
| expungeStaleAssociations(); |
| try { |
| return map.computeIfAbsent( |
| Pair.weak(k1, k2, queue), |
| pair -> mappingFunction.apply(pair.first(), pair.second())); |
| } finally { |
| Reference.reachabilityFence(k1); |
| Reference.reachabilityFence(k2); |
| } |
| } |
| |
| /** |
| * Returns a {@link Collection} view of the values contained in this |
| * WeakPairMap. The collection is backed by the WeakPairMap, so changes to |
| * the map are reflected in the collection, and vice-versa. The collection |
| * supports element removal, which removes the corresponding |
| * mapping from this map, via the {@code Iterator.remove}, |
| * {@code Collection.remove}, {@code removeAll}, |
| * {@code retainAll}, and {@code clear} operations. It does not |
| * support the {@code add} or {@code addAll} operations. |
| * |
| * @return the collection view |
| */ |
| public Collection<V> values() { |
| expungeStaleAssociations(); |
| return map.values(); |
| } |
| |
| /** |
| * Removes associations from this WeakPairMap for which at least one of the |
| * keys in key pair has been found weakly-reachable and corresponding |
| * WeakRefPeer(s) enqueued. Called as part of each public operation. |
| */ |
| private void expungeStaleAssociations() { |
| WeakRefPeer<?> peer; |
| while ((peer = (WeakRefPeer<?>) queue.poll()) != null) { |
| map.remove(peer.weakPair()); |
| } |
| } |
| |
| /** |
| * Common interface of both {@link Weak} and {@link Lookup} key pairs. |
| */ |
| private interface Pair<K1, K2> { |
| |
| static <K1, K2> Pair<K1, K2> weak(K1 k1, K2 k2, |
| ReferenceQueue<Object> queue) { |
| return new Weak<>(k1, k2, queue); |
| } |
| |
| static <K1, K2> Pair<K1, K2> lookup(K1 k1, K2 k2) { |
| return new Lookup<>(k1, k2); |
| } |
| |
| /** |
| * @return The 1st of the pair of keys (may be null for {@link Weak} |
| * when it gets cleared) |
| */ |
| K1 first(); |
| |
| /** |
| * @return The 2nd of the pair of keys (may be null for {@link Weak} |
| * when it gets cleared) |
| */ |
| K2 second(); |
| |
| static int hashCode(Object first, Object second) { |
| // assert first != null && second != null; |
| return System.identityHashCode(first) ^ |
| System.identityHashCode(second); |
| } |
| |
| static boolean equals(Object first, Object second, Pair<?, ?> p) { |
| return first != null && second != null && |
| first == p.first() && second == p.second(); |
| } |
| |
| /** |
| * A Pair where both keys are weakly-referenced. |
| * It is composed of two instances of {@link WeakRefPeer}s: |
| * <pre>{@code |
| * |
| * +-referent-> [K1] +-referent-> [K2] |
| * | | |
| * +----------------+ +----------------+ |
| * | Pair.Weak <: |-----peer----->| (anonymous) <: | |
| * | WeakRefPeer, | | WeakRefPeer | |
| * | Pair |<--weakPair()--| | |
| * +----------------+ +----------------+ |
| * | ^ |
| * | | |
| * +-weakPair()-+ |
| * |
| * }</pre> |
| * <p> |
| * Pair.Weak is used for CHM keys. Both peers are associated with the |
| * same {@link ReferenceQueue} so when either of their referents |
| * becomes weakly-reachable, the corresponding entries can be |
| * {@link #expungeStaleAssociations() expunged} from the map. |
| */ |
| final class Weak<K1, K2> extends WeakRefPeer<K1> implements Pair<K1, K2> { |
| |
| // saved hash so it can be retrieved after the reference is cleared |
| private final int hash; |
| // link to <K2> peer |
| private final WeakRefPeer<K2> peer; |
| |
| Weak(K1 k1, K2 k2, ReferenceQueue<Object> queue) { |
| super(k1, queue); |
| hash = Pair.hashCode(k1, k2); |
| peer = new WeakRefPeer<>(k2, queue) { |
| // link back to <K1> peer |
| @Override |
| Weak<?, ?> weakPair() { return Weak.this; } |
| }; |
| } |
| |
| @Override |
| Weak<?, ?> weakPair() { |
| return this; |
| } |
| |
| @Override |
| public K1 first() { |
| return get(); |
| } |
| |
| @Override |
| public K2 second() { |
| return peer.get(); |
| } |
| |
| @Override |
| public int hashCode() { |
| return hash; |
| } |
| |
| @Override |
| public boolean equals(Object obj) { |
| return this == obj || |
| (obj instanceof Pair && |
| Pair.equals(first(), second(), (Pair<?, ?>) obj)); |
| } |
| } |
| |
| /** |
| * Optimized lookup Pair, used as lookup key in methods like |
| * {@link java.util.Map#get(Object)} or |
| * {@link java.util.Map#containsKey(Object)}) where |
| * there is a great chance its allocation is eliminated |
| * by escape analysis when such lookups are inlined by JIT. |
| * All its methods are purposely designed so that 'this' is never |
| * passed to any other method or used as identity. |
| */ |
| final class Lookup<K1, K2> implements Pair<K1, K2> { |
| private final K1 k1; |
| private final K2 k2; |
| |
| Lookup(K1 k1, K2 k2) { |
| this.k1 = Objects.requireNonNull(k1); |
| this.k2 = Objects.requireNonNull(k2); |
| } |
| |
| @Override |
| public K1 first() { |
| return k1; |
| } |
| |
| @Override |
| public K2 second() { |
| return k2; |
| } |
| |
| @Override |
| public int hashCode() { |
| return Pair.hashCode(k1, k2); |
| } |
| |
| @Override |
| public boolean equals(Object obj) { |
| return obj instanceof Pair && |
| Pair.equals(k1, k2, (Pair<?, ?>) obj); |
| } |
| } |
| } |
| |
| /** |
| * Common abstract supertype of a pair of WeakReference peers. |
| */ |
| private static abstract class WeakRefPeer<K> extends WeakReference<K> { |
| |
| WeakRefPeer(K k, ReferenceQueue<Object> queue) { |
| super(Objects.requireNonNull(k), queue); |
| } |
| |
| /** |
| * @return the {@link Pair.Weak} side of the pair of peers. |
| */ |
| abstract Pair.Weak<?, ?> weakPair(); |
| } |
| } |
