--- a/jdk/src/java.base/share/classes/java/lang/reflect/WeakPairMap.java Thu Apr 13 20:35:05 2017 +0000
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,354 +0,0 @@
-/*
- * 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.reflect;
-
-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();
- }
-}