1502 lines
50 KiB
Java
1502 lines
50 KiB
Java
/*
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* Copyright 2011 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/licenses/publicdomain
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*/
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package io.netty.util.internal;
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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.WeakReference;
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import java.util.AbstractCollection;
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import java.util.AbstractMap;
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import java.util.AbstractSet;
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import java.util.Collection;
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import java.util.ConcurrentModificationException;
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import java.util.Enumeration;
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import java.util.Hashtable;
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import java.util.Iterator;
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import java.util.Map;
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import java.util.NoSuchElementException;
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import java.util.Set;
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import java.util.concurrent.ConcurrentMap;
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import java.util.concurrent.locks.ReentrantLock;
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/**
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* An alternative weak-key {@link ConcurrentMap} which is similar to
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* {@link java.util.concurrent.ConcurrentHashMap}.
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* @param <K> the type of keys maintained by this map
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* @param <V> the type of mapped values
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*/
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public final class ConcurrentWeakKeyHashMap<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {
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/*
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* The basic strategy is to subdivide the table among Segments,
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* each of which itself is a concurrently readable hash table.
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*/
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/**
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* The default initial capacity for this table, used when not otherwise
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* specified in a constructor.
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*/
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static final int DEFAULT_INITIAL_CAPACITY = 16;
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/**
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* The default load factor for this table, used when not otherwise specified
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* in a constructor.
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*/
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static final float DEFAULT_LOAD_FACTOR = 0.75f;
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/**
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* The default concurrency level for this table, used when not otherwise
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* specified in a constructor.
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*/
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static final int DEFAULT_CONCURRENCY_LEVEL = 16;
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/**
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* The maximum capacity, used if a higher value is implicitly specified by
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* either of the constructors with arguments. MUST be a power of two
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* <= 1<<30 to ensure that entries are indexable using integers.
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*/
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static final int MAXIMUM_CAPACITY = 1 << 30;
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/**
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* The maximum number of segments to allow; used to bound constructor
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* arguments.
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*/
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static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
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/**
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* Number of unsynchronized retries in size and containsValue methods before
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* resorting to locking. This is used to avoid unbounded retries if tables
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* undergo continuous modification which would make it impossible to obtain
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* an accurate result.
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*/
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static final int RETRIES_BEFORE_LOCK = 2;
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/* ---------------- Fields -------------- */
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/**
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* Mask value for indexing into segments. The upper bits of a key's hash
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* code are used to choose the segment.
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*/
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final int segmentMask;
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/**
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* Shift value for indexing within segments.
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*/
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final int segmentShift;
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/**
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* The segments, each of which is a specialized hash table
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*/
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final Segment<K, V>[] segments;
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Set<K> keySet;
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Set<Map.Entry<K, V>> entrySet;
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Collection<V> values;
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/* ---------------- Small Utilities -------------- */
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/**
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* Applies a supplemental hash function to a given hashCode, which defends
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* against poor quality hash functions. This is critical because
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* ConcurrentReferenceHashMap uses power-of-two length hash tables, that
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* otherwise encounter collisions for hashCodes that do not differ in lower
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* or upper bits.
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*/
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private static int hash(int h) {
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// Spread bits to regularize both segment and index locations,
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// using variant of single-word Wang/Jenkins hash.
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h += h << 15 ^ 0xffffcd7d;
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h ^= h >>> 10;
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h += h << 3;
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h ^= h >>> 6;
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h += (h << 2) + (h << 14);
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return h ^ h >>> 16;
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}
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/**
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* Returns the segment that should be used for key with given hash.
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*
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* @param hash the hash code for the key
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* @return the segment
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*/
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Segment<K, V> segmentFor(int hash) {
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return segments[hash >>> segmentShift & segmentMask];
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}
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private int hashOf(Object key) {
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return hash(key.hashCode());
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}
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/* ---------------- Inner Classes -------------- */
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/**
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* A weak-key reference which stores the key hash needed for reclamation.
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*/
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static final class WeakKeyReference<K> extends WeakReference<K> {
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final int hash;
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WeakKeyReference(K key, int hash, ReferenceQueue<Object> refQueue) {
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super(key, refQueue);
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this.hash = hash;
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}
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public int keyHash() {
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return hash;
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}
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public Object keyRef() {
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return this;
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}
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}
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/**
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* ConcurrentReferenceHashMap list entry. Note that this is never exported
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* out as a user-visible Map.Entry.
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*
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* Because the value field is volatile, not final, it is legal wrt
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* the Java Memory Model for an unsynchronized reader to see null
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* instead of initial value when read via a data race. Although a
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* reordering leading to this is not likely to ever actually
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* occur, the Segment.readValueUnderLock method is used as a
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* backup in case a null (pre-initialized) value is ever seen in
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* an unsynchronized access method.
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*/
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static final class HashEntry<K, V> {
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final Object keyRef;
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final int hash;
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volatile Object valueRef;
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final HashEntry<K, V> next;
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HashEntry(
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K key, int hash, HashEntry<K, V> next, V value,
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ReferenceQueue<Object> refQueue) {
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this.hash = hash;
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this.next = next;
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this.keyRef = new WeakKeyReference<K>(key, hash, refQueue);
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this.valueRef = value;
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}
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@SuppressWarnings("unchecked")
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K key() {
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return ((WeakReference<K>) keyRef).get();
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}
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V value() {
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return dereferenceValue(valueRef);
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}
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@SuppressWarnings("unchecked")
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V dereferenceValue(Object value) {
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if (value instanceof WeakKeyReference) {
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return ((Reference<V>) value).get();
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}
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return (V) value;
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}
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void setValue(V value) {
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this.valueRef = value;
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}
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@SuppressWarnings("unchecked")
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static <K, V> HashEntry<K, V>[] newArray(int i) {
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return new HashEntry[i];
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}
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}
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/**
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* Segments are specialized versions of hash tables. This subclasses from
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* ReentrantLock opportunistically, just to simplify some locking and avoid
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* separate construction.
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*/
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static final class Segment<K, V> extends ReentrantLock {
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/*
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* Segments maintain a table of entry lists that are ALWAYS kept in a
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* consistent state, so can be read without locking. Next fields of
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* nodes are immutable (final). All list additions are performed at the
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* front of each bin. This makes it easy to check changes, and also fast
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* to traverse. When nodes would otherwise be changed, new nodes are
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* created to replace them. This works well for hash tables since the
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* bin lists tend to be short. (The average length is less than two for
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* the default load factor threshold.)
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*
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* Read operations can thus proceed without locking, but rely on
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* selected uses of volatiles to ensure that completed write operations
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* performed by other threads are noticed. For most purposes, the
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* "count" field, tracking the number of elements, serves as that
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* volatile variable ensuring visibility. This is convenient because
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* this field needs to be read in many read operations anyway:
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*
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* - All (unsynchronized) read operations must first read the
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* "count" field, and should not look at table entries if
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* it is 0.
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*
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* - All (synchronized) write operations should write to
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* the "count" field after structurally changing any bin.
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* The operations must not take any action that could even
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* momentarily cause a concurrent read operation to see
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* inconsistent data. This is made easier by the nature of
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* the read operations in Map. For example, no operation
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* can reveal that the table has grown but the threshold
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* has not yet been updated, so there are no atomicity
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* requirements for this with respect to reads.
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*
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* As a guide, all critical volatile reads and writes to the count field
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* are marked in code comments.
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*/
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private static final long serialVersionUID = -8328104880676891126L;
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/**
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* The number of elements in this segment's region.
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*/
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transient volatile int count;
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/**
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* Number of updates that alter the size of the table. This is used
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* during bulk-read methods to make sure they see a consistent snapshot:
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* If modCounts change during a traversal of segments computing size or
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* checking containsValue, then we might have an inconsistent view of
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* state so (usually) must retry.
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*/
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int modCount;
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/**
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* The table is rehashed when its size exceeds this threshold.
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* (The value of this field is always <tt>(capacity * loadFactor)</tt>.)
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*/
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int threshold;
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/**
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* The per-segment table.
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*/
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transient volatile HashEntry<K, V>[] table;
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/**
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* The load factor for the hash table. Even though this value is same
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* for all segments, it is replicated to avoid needing links to outer
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* object.
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*/
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final float loadFactor;
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/**
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* The collected weak-key reference queue for this segment. This should
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* be (re)initialized whenever table is assigned,
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*/
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transient volatile ReferenceQueue<Object> refQueue;
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Segment(int initialCapacity, float lf) {
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loadFactor = lf;
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setTable(HashEntry.<K, V>newArray(initialCapacity));
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}
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@SuppressWarnings("unchecked")
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static <K, V> Segment<K, V>[] newArray(int i) {
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return new Segment[i];
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}
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private boolean keyEq(Object src, Object dest) {
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return src.equals(dest);
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}
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/**
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* Sets table to new HashEntry array. Call only while holding lock or in
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* constructor.
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*/
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void setTable(HashEntry<K, V>[] newTable) {
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threshold = (int) (newTable.length * loadFactor);
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table = newTable;
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refQueue = new ReferenceQueue<Object>();
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}
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/**
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* Returns properly casted first entry of bin for given hash.
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*/
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HashEntry<K, V> getFirst(int hash) {
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HashEntry<K, V>[] tab = table;
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return tab[hash & tab.length - 1];
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}
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HashEntry<K, V> newHashEntry(
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K key, int hash, HashEntry<K, V> next, V value) {
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return new HashEntry<K, V>(
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key, hash, next, value, refQueue);
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}
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/**
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* Reads value field of an entry under lock. Called if value field ever
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* appears to be null. This is possible only if a compiler happens to
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* reorder a HashEntry initialization with its table assignment, which
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* is legal under memory model but is not known to ever occur.
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*/
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V readValueUnderLock(HashEntry<K, V> e) {
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lock();
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try {
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removeStale();
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return e.value();
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} finally {
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unlock();
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}
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}
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/* Specialized implementations of map methods */
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V get(Object key, int hash) {
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if (count != 0) { // read-volatile
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HashEntry<K, V> e = getFirst(hash);
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while (e != null) {
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if (e.hash == hash && keyEq(key, e.key())) {
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Object opaque = e.valueRef;
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if (opaque != null) {
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return e.dereferenceValue(opaque);
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}
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return readValueUnderLock(e); // recheck
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}
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e = e.next;
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}
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}
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return null;
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}
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boolean containsKey(Object key, int hash) {
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if (count != 0) { // read-volatile
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HashEntry<K, V> e = getFirst(hash);
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while (e != null) {
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if (e.hash == hash && keyEq(key, e.key())) {
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return true;
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}
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e = e.next;
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}
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}
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return false;
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}
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boolean containsValue(Object value) {
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if (count != 0) { // read-volatile
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HashEntry<K, V>[] tab = table;
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int len = tab.length;
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for (int i = 0; i < len; i ++) {
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for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
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Object opaque = e.valueRef;
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V v;
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if (opaque == null) {
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v = readValueUnderLock(e); // recheck
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} else {
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v = e.dereferenceValue(opaque);
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}
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if (value.equals(v)) {
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return true;
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}
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}
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}
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}
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return false;
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}
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boolean replace(K key, int hash, V oldValue, V newValue) {
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lock();
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try {
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removeStale();
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HashEntry<K, V> e = getFirst(hash);
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while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
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e = e.next;
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}
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boolean replaced = false;
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if (e != null && oldValue.equals(e.value())) {
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replaced = true;
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e.setValue(newValue);
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}
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return replaced;
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} finally {
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unlock();
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}
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}
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V replace(K key, int hash, V newValue) {
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lock();
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try {
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removeStale();
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HashEntry<K, V> e = getFirst(hash);
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while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
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e = e.next;
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}
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V oldValue = null;
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if (e != null) {
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oldValue = e.value();
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e.setValue(newValue);
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}
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return oldValue;
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} finally {
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unlock();
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}
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}
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V put(K key, int hash, V value, boolean onlyIfAbsent) {
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lock();
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try {
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removeStale();
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int c = count;
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if (c ++ > threshold) { // ensure capacity
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int reduced = rehash();
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if (reduced > 0) {
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count = (c -= reduced) - 1; // write-volatile
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}
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}
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HashEntry<K, V>[] tab = table;
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int index = hash & tab.length - 1;
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HashEntry<K, V> first = tab[index];
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HashEntry<K, V> e = first;
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while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
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e = e.next;
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}
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V oldValue;
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if (e != null) {
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oldValue = e.value();
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if (!onlyIfAbsent) {
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e.setValue(value);
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}
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} else {
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oldValue = null;
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++ modCount;
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tab[index] = newHashEntry(key, hash, first, value);
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count = c; // write-volatile
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}
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return oldValue;
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} finally {
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unlock();
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}
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}
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int rehash() {
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HashEntry<K, V>[] oldTable = table;
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int oldCapacity = oldTable.length;
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if (oldCapacity >= MAXIMUM_CAPACITY) {
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return 0;
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}
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/*
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* Reclassify nodes in each list to new Map. Because we are using
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* power-of-two expansion, the elements from each bin must either
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* stay at same index, or move with a power of two offset. We
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* eliminate unnecessary node creation by catching cases where old
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* nodes can be reused because their next fields won't change.
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* Statistically, at the default threshold, only about one-sixth of
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* them need cloning when a table doubles. The nodes they replace
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* will be garbage collectable as soon as they are no longer
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* referenced by any reader thread that may be in the midst of
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* traversing table right now.
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*/
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HashEntry<K, V>[] newTable = HashEntry.newArray(oldCapacity << 1);
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threshold = (int) (newTable.length * loadFactor);
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int sizeMask = newTable.length - 1;
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int reduce = 0;
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for (int i = 0; i < oldCapacity; i ++) {
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// We need to guarantee that any existing reads of old Map can
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// proceed. So we cannot yet null out each bin.
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HashEntry<K, V> e = oldTable[i];
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if (e != null) {
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HashEntry<K, V> next = e.next;
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int idx = e.hash & sizeMask;
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// Single node on list
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if (next == null) {
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newTable[idx] = e;
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} else {
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// Reuse trailing consecutive sequence at same slot
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HashEntry<K, V> lastRun = e;
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int lastIdx = idx;
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for (HashEntry<K, V> last = next; last != null; last = last.next) {
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int k = last.hash & sizeMask;
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if (k != lastIdx) {
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lastIdx = k;
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lastRun = last;
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}
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}
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newTable[lastIdx] = lastRun;
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// Clone all remaining nodes
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for (HashEntry<K, V> p = e; p != lastRun; p = p.next) {
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// Skip GC'd weak references
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K key = p.key();
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if (key == null) {
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reduce ++;
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continue;
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}
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int k = p.hash & sizeMask;
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HashEntry<K, V> n = newTable[k];
|
|
newTable[k] = newHashEntry(key, p.hash, n, p.value());
|
|
}
|
|
}
|
|
}
|
|
}
|
|
table = newTable;
|
|
return reduce;
|
|
}
|
|
|
|
/**
|
|
* Remove; match on key only if value null, else match both.
|
|
*/
|
|
V remove(Object key, int hash, Object value, boolean refRemove) {
|
|
lock();
|
|
try {
|
|
if (!refRemove) {
|
|
removeStale();
|
|
}
|
|
int c = count - 1;
|
|
HashEntry<K, V>[] tab = table;
|
|
int index = hash & tab.length - 1;
|
|
HashEntry<K, V> first = tab[index];
|
|
HashEntry<K, V> e = first;
|
|
// a reference remove operation compares the Reference instance
|
|
while (e != null && key != e.keyRef &&
|
|
(refRemove || hash != e.hash || !keyEq(key, e.key()))) {
|
|
e = e.next;
|
|
}
|
|
|
|
V oldValue = null;
|
|
if (e != null) {
|
|
V v = e.value();
|
|
if (value == null || value.equals(v)) {
|
|
oldValue = v;
|
|
// All entries following removed node can stay in list,
|
|
// but all preceding ones need to be cloned.
|
|
++ modCount;
|
|
HashEntry<K, V> newFirst = e.next;
|
|
for (HashEntry<K, V> p = first; p != e; p = p.next) {
|
|
K pKey = p.key();
|
|
if (pKey == null) { // Skip GC'd keys
|
|
c --;
|
|
continue;
|
|
}
|
|
|
|
newFirst = newHashEntry(
|
|
pKey, p.hash, newFirst, p.value());
|
|
}
|
|
tab[index] = newFirst;
|
|
count = c; // write-volatile
|
|
}
|
|
}
|
|
return oldValue;
|
|
} finally {
|
|
unlock();
|
|
}
|
|
}
|
|
|
|
@SuppressWarnings("rawtypes")
|
|
void removeStale() {
|
|
WeakKeyReference ref;
|
|
while ((ref = (WeakKeyReference) refQueue.poll()) != null) {
|
|
remove(ref.keyRef(), ref.keyHash(), null, true);
|
|
}
|
|
}
|
|
|
|
void clear() {
|
|
if (count != 0) {
|
|
lock();
|
|
try {
|
|
HashEntry<K, V>[] tab = table;
|
|
for (int i = 0; i < tab.length; i ++) {
|
|
tab[i] = null;
|
|
}
|
|
++ modCount;
|
|
// replace the reference queue to avoid unnecessary stale
|
|
// cleanups
|
|
refQueue = new ReferenceQueue<Object>();
|
|
count = 0; // write-volatile
|
|
} finally {
|
|
unlock();
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* ---------------- Public operations -------------- */
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial capacity, load factor
|
|
* and concurrency level.
|
|
*
|
|
* @param initialCapacity the initial capacity. The implementation performs
|
|
* internal sizing to accommodate this many elements.
|
|
* @param loadFactor the load factor threshold, used to control resizing.
|
|
* Resizing may be performed when the average number of
|
|
* elements per bin exceeds this threshold.
|
|
* @param concurrencyLevel the estimated number of concurrently updating
|
|
* threads. The implementation performs internal
|
|
* sizing to try to accommodate this many threads.
|
|
* @throws IllegalArgumentException if the initial capacity is negative or
|
|
* the load factor or concurrencyLevel are
|
|
* nonpositive.
|
|
*/
|
|
public ConcurrentWeakKeyHashMap(
|
|
int initialCapacity, float loadFactor, int concurrencyLevel) {
|
|
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0) {
|
|
throw new IllegalArgumentException();
|
|
}
|
|
|
|
if (concurrencyLevel > MAX_SEGMENTS) {
|
|
concurrencyLevel = MAX_SEGMENTS;
|
|
}
|
|
|
|
// Find power-of-two sizes best matching arguments
|
|
int sshift = 0;
|
|
int ssize = 1;
|
|
while (ssize < concurrencyLevel) {
|
|
++ sshift;
|
|
ssize <<= 1;
|
|
}
|
|
segmentShift = 32 - sshift;
|
|
segmentMask = ssize - 1;
|
|
this.segments = Segment.newArray(ssize);
|
|
|
|
if (initialCapacity > MAXIMUM_CAPACITY) {
|
|
initialCapacity = MAXIMUM_CAPACITY;
|
|
}
|
|
int c = initialCapacity / ssize;
|
|
if (c * ssize < initialCapacity) {
|
|
++ c;
|
|
}
|
|
int cap = 1;
|
|
while (cap < c) {
|
|
cap <<= 1;
|
|
}
|
|
|
|
for (int i = 0; i < this.segments.length; ++ i) {
|
|
this.segments[i] = new Segment<K, V>(cap, loadFactor);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial capacity and load
|
|
* factor and with the default reference types (weak keys, strong values),
|
|
* and concurrencyLevel (16).
|
|
*
|
|
* @param initialCapacity The implementation performs internal sizing to
|
|
* accommodate this many elements.
|
|
* @param loadFactor the load factor threshold, used to control resizing.
|
|
* Resizing may be performed when the average number of
|
|
* elements per bin exceeds this threshold.
|
|
* @throws IllegalArgumentException if the initial capacity of elements is
|
|
* negative or the load factor is
|
|
* nonpositive
|
|
*/
|
|
public ConcurrentWeakKeyHashMap(int initialCapacity, float loadFactor) {
|
|
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with the specified initial capacity, and with
|
|
* default reference types (weak keys, strong values), load factor (0.75)
|
|
* and concurrencyLevel (16).
|
|
*
|
|
* @param initialCapacity the initial capacity. The implementation performs
|
|
* internal sizing to accommodate this many elements.
|
|
* @throws IllegalArgumentException if the initial capacity of elements is
|
|
* negative.
|
|
*/
|
|
public ConcurrentWeakKeyHashMap(int initialCapacity) {
|
|
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new, empty map with a default initial capacity (16), reference
|
|
* types (weak keys, strong values), default load factor (0.75) and
|
|
* concurrencyLevel (16).
|
|
*/
|
|
public ConcurrentWeakKeyHashMap() {
|
|
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
|
|
}
|
|
|
|
/**
|
|
* Creates a new map with the same mappings as the given map. The map is
|
|
* created with a capacity of 1.5 times the number of mappings in the given
|
|
* map or 16 (whichever is greater), and a default load factor (0.75) and
|
|
* concurrencyLevel (16).
|
|
*
|
|
* @param m the map
|
|
*/
|
|
public ConcurrentWeakKeyHashMap(Map<? extends K, ? extends V> m) {
|
|
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
|
|
DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR,
|
|
DEFAULT_CONCURRENCY_LEVEL);
|
|
putAll(m);
|
|
}
|
|
|
|
/**
|
|
* Returns <tt>true</tt> if this map contains no key-value mappings.
|
|
*
|
|
* @return <tt>true</tt> if this map contains no key-value mappings
|
|
*/
|
|
@Override
|
|
public boolean isEmpty() {
|
|
final Segment<K, V>[] segments = this.segments;
|
|
/*
|
|
* We keep track of per-segment modCounts to avoid ABA problems in which
|
|
* an element in one segment was added and in another removed during
|
|
* traversal, in which case the table was never actually empty at any
|
|
* point. Note the similar use of modCounts in the size() and
|
|
* containsValue() methods, which are the only other methods also
|
|
* susceptible to ABA problems.
|
|
*/
|
|
int[] mc = new int[segments.length];
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
if (segments[i].count != 0) {
|
|
return false;
|
|
} else {
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
}
|
|
}
|
|
// If mcsum happens to be zero, then we know we got a snapshot before
|
|
// any modifications at all were made. This is probably common enough
|
|
// to bother tracking.
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
if (segments[i].count != 0 || mc[i] != segments[i].modCount) {
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/**
|
|
* Returns the number of key-value mappings in this map. If the map contains
|
|
* more than <tt>Integer.MAX_VALUE</tt> elements, returns
|
|
* <tt>Integer.MAX_VALUE</tt>.
|
|
*
|
|
* @return the number of key-value mappings in this map
|
|
*/
|
|
@Override
|
|
public int size() {
|
|
final Segment<K, V>[] segments = this.segments;
|
|
long sum = 0;
|
|
long check = 0;
|
|
int[] mc = new int[segments.length];
|
|
// Try a few times to get accurate count. On failure due to continuous
|
|
// async changes in table, resort to locking.
|
|
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++ k) {
|
|
check = 0;
|
|
sum = 0;
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
sum += segments[i].count;
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
}
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
check += segments[i].count;
|
|
if (mc[i] != segments[i].modCount) {
|
|
check = -1; // force retry
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (check == sum) {
|
|
break;
|
|
}
|
|
}
|
|
if (check != sum) { // Resort to locking all segments
|
|
sum = 0;
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].lock();
|
|
}
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
sum += segments[i].count;
|
|
}
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].unlock();
|
|
}
|
|
}
|
|
if (sum > Integer.MAX_VALUE) {
|
|
return Integer.MAX_VALUE;
|
|
} else {
|
|
return (int) sum;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns the value to which the specified key is mapped, or {@code null}
|
|
* if this map contains no mapping for the key.
|
|
*
|
|
* <p>More formally, if this map contains a mapping from a key {@code k} to
|
|
* a value {@code v} such that {@code key.equals(k)}, then this method
|
|
* returns {@code v}; otherwise it returns {@code null}. (There can be at
|
|
* most one such mapping.)
|
|
*
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
@Override
|
|
public V get(Object key) {
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).get(key, hash);
|
|
}
|
|
|
|
/**
|
|
* Tests if the specified object is a key in this table.
|
|
*
|
|
* @param key possible key
|
|
* @return <tt>true</tt> if and only if the specified object is a key in
|
|
* this table, as determined by the <tt>equals</tt> method;
|
|
* <tt>false</tt> otherwise.
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
@Override
|
|
public boolean containsKey(Object key) {
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).containsKey(key, hash);
|
|
}
|
|
|
|
/**
|
|
* Returns <tt>true</tt> if this map maps one or more keys to the specified
|
|
* value. Note: This method requires a full internal traversal of the hash
|
|
* table, and so is much slower than method <tt>containsKey</tt>.
|
|
*
|
|
* @param value value whose presence in this map is to be tested
|
|
* @return <tt>true</tt> if this map maps one or more keys to the specified
|
|
* value
|
|
* @throws NullPointerException if the specified value is null
|
|
*/
|
|
|
|
@Override
|
|
public boolean containsValue(Object value) {
|
|
if (value == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
|
|
// See explanation of modCount use above
|
|
|
|
final Segment<K, V>[] segments = this.segments;
|
|
int[] mc = new int[segments.length];
|
|
|
|
// Try a few times without locking
|
|
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++ k) {
|
|
int mcsum = 0;
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
mcsum += mc[i] = segments[i].modCount;
|
|
if (segments[i].containsValue(value)) {
|
|
return true;
|
|
}
|
|
}
|
|
boolean cleanSweep = true;
|
|
if (mcsum != 0) {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
if (mc[i] != segments[i].modCount) {
|
|
cleanSweep = false;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
if (cleanSweep) {
|
|
return false;
|
|
}
|
|
}
|
|
// Resort to locking all segments
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].lock();
|
|
}
|
|
boolean found = false;
|
|
try {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
if (segments[i].containsValue(value)) {
|
|
found = true;
|
|
break;
|
|
}
|
|
}
|
|
} finally {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].unlock();
|
|
}
|
|
}
|
|
return found;
|
|
}
|
|
|
|
/**
|
|
* Legacy method testing if some key maps into the specified value in this
|
|
* table. This method is identical in functionality to
|
|
* {@link #containsValue}, and exists solely to ensure full compatibility
|
|
* with class {@link Hashtable}, which supported this method prior to
|
|
* introduction of the Java Collections framework.
|
|
*
|
|
* @param value a value to search for
|
|
* @return <tt>true</tt> if and only if some key maps to the <tt>value</tt>
|
|
* argument in this table as determined by the <tt>equals</tt>
|
|
* method; <tt>false</tt> otherwise
|
|
* @throws NullPointerException if the specified value is null
|
|
*/
|
|
public boolean contains(Object value) {
|
|
return containsValue(value);
|
|
}
|
|
|
|
/**
|
|
* Maps the specified key to the specified value in this table. Neither the
|
|
* key nor the value can be null.
|
|
*
|
|
* <p>The value can be retrieved by calling the <tt>get</tt> method with a
|
|
* key that is equal to the original key.
|
|
*
|
|
* @param key key with which the specified value is to be associated
|
|
* @param value value to be associated with the specified key
|
|
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt>
|
|
* if there was no mapping for <tt>key</tt>
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
@Override
|
|
public V put(K key, V value) {
|
|
if (value == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).put(key, hash, value, false);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @return the previous value associated with the specified key, or
|
|
* <tt>null</tt> if there was no mapping for the key
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
@Override
|
|
public V putIfAbsent(K key, V value) {
|
|
if (value == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).put(key, hash, value, true);
|
|
}
|
|
|
|
/**
|
|
* Copies all of the mappings from the specified map to this one. These
|
|
* mappings replace any mappings that this map had for any of the keys
|
|
* currently in the specified map.
|
|
*
|
|
* @param m mappings to be stored in this map
|
|
*/
|
|
@Override
|
|
public void putAll(Map<? extends K, ? extends V> m) {
|
|
for (Map.Entry<? extends K, ? extends V> e: m.entrySet()) {
|
|
put(e.getKey(), e.getValue());
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Removes the key (and its corresponding value) from this map. This method
|
|
* does nothing if the key is not in the map.
|
|
*
|
|
* @param key the key that needs to be removed
|
|
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt>
|
|
* if there was no mapping for <tt>key</tt>
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
@Override
|
|
public V remove(Object key) {
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).remove(key, hash, null, false);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @throws NullPointerException if the specified key is null
|
|
*/
|
|
@Override
|
|
public boolean remove(Object key, Object value) {
|
|
int hash = hashOf(key);
|
|
if (value == null) {
|
|
return false;
|
|
}
|
|
return segmentFor(hash).remove(key, hash, value, false) != null;
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @throws NullPointerException if any of the arguments are null
|
|
*/
|
|
@Override
|
|
public boolean replace(K key, V oldValue, V newValue) {
|
|
if (oldValue == null || newValue == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).replace(key, hash, oldValue, newValue);
|
|
}
|
|
|
|
/**
|
|
* {@inheritDoc}
|
|
*
|
|
* @return the previous value associated with the specified key, or
|
|
* <tt>null</tt> if there was no mapping for the key
|
|
* @throws NullPointerException if the specified key or value is null
|
|
*/
|
|
@Override
|
|
public V replace(K key, V value) {
|
|
if (value == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
int hash = hashOf(key);
|
|
return segmentFor(hash).replace(key, hash, value);
|
|
}
|
|
|
|
/**
|
|
* Removes all of the mappings from this map.
|
|
*/
|
|
@Override
|
|
public void clear() {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].clear();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Removes any stale entries whose keys have been finalized. Use of this
|
|
* method is normally not necessary since stale entries are automatically
|
|
* removed lazily, when blocking operations are required. However, there are
|
|
* some cases where this operation should be performed eagerly, such as
|
|
* cleaning up old references to a ClassLoader in a multi-classloader
|
|
* environment.
|
|
*
|
|
* Note: this method will acquire locks, one at a time, across all segments
|
|
* of this table, so if it is to be used, it should be used sparingly.
|
|
*/
|
|
public void purgeStaleEntries() {
|
|
for (int i = 0; i < segments.length; ++ i) {
|
|
segments[i].removeStale();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Set} view of the keys contained in this map. The set is
|
|
* backed by the map, so changes to the map are reflected in the set, and
|
|
* vice-versa. The set supports element removal, which removes the
|
|
* corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
|
|
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
|
|
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or
|
|
* <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that
|
|
* will never throw {@link ConcurrentModificationException}, and guarantees
|
|
* to traverse elements as they existed upon construction of the iterator,
|
|
* and may (but is not guaranteed to) reflect any modifications subsequent
|
|
* to construction.
|
|
*/
|
|
@Override
|
|
public Set<K> keySet() {
|
|
Set<K> ks = keySet;
|
|
return ks != null? ks : (keySet = new KeySet());
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Collection} view of the values contained in this map.
|
|
* The collection is backed by the map, 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
|
|
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>, <tt>removeAll</tt>,
|
|
* <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support
|
|
* the <tt>add</tt> or <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that
|
|
* will never throw {@link ConcurrentModificationException}, and guarantees
|
|
* to traverse elements as they existed upon construction of the iterator,
|
|
* and may (but is not guaranteed to) reflect any modifications subsequent
|
|
* to construction.
|
|
*/
|
|
@Override
|
|
public Collection<V> values() {
|
|
Collection<V> vs = values;
|
|
return vs != null? vs : (values = new Values());
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link Set} view of the mappings contained in this map.
|
|
* The set is backed by the map, so changes to the map are reflected in the
|
|
* set, and vice-versa. The set supports element removal, which removes the
|
|
* corresponding mapping from the map, via the <tt>Iterator.remove</tt>,
|
|
* <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and
|
|
* <tt>clear</tt> operations. It does not support the <tt>add</tt> or
|
|
* <tt>addAll</tt> operations.
|
|
*
|
|
* <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator that
|
|
* will never throw {@link ConcurrentModificationException}, and guarantees
|
|
* to traverse elements as they existed upon construction of the iterator,
|
|
* and may (but is not guaranteed to) reflect any modifications subsequent
|
|
* to construction.
|
|
*/
|
|
@Override
|
|
public Set<Map.Entry<K, V>> entrySet() {
|
|
Set<Map.Entry<K, V>> es = entrySet;
|
|
return es != null? es : (entrySet = new EntrySet());
|
|
}
|
|
|
|
/**
|
|
* Returns an enumeration of the keys in this table.
|
|
*
|
|
* @return an enumeration of the keys in this table
|
|
* @see #keySet()
|
|
*/
|
|
public Enumeration<K> keys() {
|
|
return new KeyIterator();
|
|
}
|
|
|
|
/**
|
|
* Returns an enumeration of the values in this table.
|
|
*
|
|
* @return an enumeration of the values in this table
|
|
* @see #values()
|
|
*/
|
|
public Enumeration<V> elements() {
|
|
return new ValueIterator();
|
|
}
|
|
|
|
/* ---------------- Iterator Support -------------- */
|
|
|
|
abstract class HashIterator {
|
|
int nextSegmentIndex;
|
|
int nextTableIndex;
|
|
HashEntry<K, V>[] currentTable;
|
|
HashEntry<K, V> nextEntry;
|
|
HashEntry<K, V> lastReturned;
|
|
K currentKey; // Strong reference to weak key (prevents gc)
|
|
|
|
HashIterator() {
|
|
nextSegmentIndex = segments.length - 1;
|
|
nextTableIndex = -1;
|
|
advance();
|
|
}
|
|
|
|
public void rewind() {
|
|
nextSegmentIndex = segments.length - 1;
|
|
nextTableIndex = -1;
|
|
currentTable = null;
|
|
nextEntry = null;
|
|
lastReturned = null;
|
|
currentKey = null;
|
|
advance();
|
|
}
|
|
|
|
public boolean hasMoreElements() {
|
|
return hasNext();
|
|
}
|
|
|
|
final void advance() {
|
|
if (nextEntry != null && (nextEntry = nextEntry.next) != null) {
|
|
return;
|
|
}
|
|
|
|
while (nextTableIndex >= 0) {
|
|
if ((nextEntry = currentTable[nextTableIndex --]) != null) {
|
|
return;
|
|
}
|
|
}
|
|
|
|
while (nextSegmentIndex >= 0) {
|
|
Segment<K, V> seg = segments[nextSegmentIndex --];
|
|
if (seg.count != 0) {
|
|
currentTable = seg.table;
|
|
for (int j = currentTable.length - 1; j >= 0; -- j) {
|
|
if ((nextEntry = currentTable[j]) != null) {
|
|
nextTableIndex = j - 1;
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
public boolean hasNext() {
|
|
while (nextEntry != null) {
|
|
if (nextEntry.key() != null) {
|
|
return true;
|
|
}
|
|
advance();
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
HashEntry<K, V> nextEntry() {
|
|
do {
|
|
if (nextEntry == null) {
|
|
throw new NoSuchElementException();
|
|
}
|
|
|
|
lastReturned = nextEntry;
|
|
currentKey = lastReturned.key();
|
|
advance();
|
|
} while (currentKey == null); // Skip GC'd keys
|
|
|
|
return lastReturned;
|
|
}
|
|
|
|
public void remove() {
|
|
if (lastReturned == null) {
|
|
throw new IllegalStateException();
|
|
}
|
|
ConcurrentWeakKeyHashMap.this.remove(currentKey);
|
|
lastReturned = null;
|
|
}
|
|
}
|
|
|
|
final class KeyIterator
|
|
extends HashIterator implements ReusableIterator<K>, Enumeration<K> {
|
|
|
|
@Override
|
|
public K next() {
|
|
return super.nextEntry().key();
|
|
}
|
|
|
|
@Override
|
|
public K nextElement() {
|
|
return super.nextEntry().key();
|
|
}
|
|
}
|
|
|
|
final class ValueIterator
|
|
extends HashIterator implements ReusableIterator<V>, Enumeration<V> {
|
|
|
|
@Override
|
|
public V next() {
|
|
return super.nextEntry().value();
|
|
}
|
|
|
|
@Override
|
|
public V nextElement() {
|
|
return super.nextEntry().value();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* This class is needed for JDK5 compatibility.
|
|
*/
|
|
static class SimpleEntry<K, V> implements Entry<K, V> {
|
|
|
|
private final K key;
|
|
|
|
private V value;
|
|
|
|
public SimpleEntry(K key, V value) {
|
|
this.key = key;
|
|
this.value = value;
|
|
|
|
}
|
|
|
|
public SimpleEntry(Entry<? extends K, ? extends V> entry) {
|
|
this.key = entry.getKey();
|
|
this.value = entry.getValue();
|
|
|
|
}
|
|
|
|
@Override
|
|
public K getKey() {
|
|
return key;
|
|
}
|
|
|
|
@Override
|
|
public V getValue() {
|
|
return value;
|
|
}
|
|
|
|
@Override
|
|
public V setValue(V value) {
|
|
V oldValue = this.value;
|
|
this.value = value;
|
|
return oldValue;
|
|
}
|
|
|
|
@Override
|
|
public boolean equals(Object o) {
|
|
if (!(o instanceof Map.Entry<?, ?>)) {
|
|
return false;
|
|
}
|
|
@SuppressWarnings("rawtypes")
|
|
Map.Entry e = (Map.Entry) o;
|
|
return eq(key, e.getKey()) && eq(value, e.getValue());
|
|
}
|
|
|
|
@Override
|
|
public int hashCode() {
|
|
return (key == null? 0 : key.hashCode()) ^ (value == null? 0 : value.hashCode());
|
|
}
|
|
|
|
@Override
|
|
public String toString() {
|
|
return key + "=" + value;
|
|
}
|
|
|
|
private static boolean eq(Object o1, Object o2) {
|
|
return o1 == null? o2 == null : o1.equals(o2);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Custom Entry class used by EntryIterator.next(), that relays setValue
|
|
* changes to the underlying map.
|
|
*/
|
|
final class WriteThroughEntry extends SimpleEntry<K, V> {
|
|
|
|
WriteThroughEntry(K k, V v) {
|
|
super(k, v);
|
|
}
|
|
|
|
/**
|
|
* Set our entry's value and write through to the map. The value to
|
|
* return is somewhat arbitrary here. Since a WriteThroughEntry does not
|
|
* necessarily track asynchronous changes, the most recent "previous"
|
|
* value could be different from what we return (or could even have been
|
|
* removed in which case the put will re-establish). We do not and can
|
|
* not guarantee more.
|
|
*/
|
|
@Override
|
|
public V setValue(V value) {
|
|
|
|
if (value == null) {
|
|
throw new NullPointerException();
|
|
}
|
|
V v = super.setValue(value);
|
|
ConcurrentWeakKeyHashMap.this.put(getKey(), value);
|
|
return v;
|
|
}
|
|
|
|
}
|
|
|
|
final class EntryIterator extends HashIterator implements
|
|
ReusableIterator<Entry<K, V>> {
|
|
@Override
|
|
public Map.Entry<K, V> next() {
|
|
HashEntry<K, V> e = super.nextEntry();
|
|
return new WriteThroughEntry(e.key(), e.value());
|
|
}
|
|
}
|
|
|
|
final class KeySet extends AbstractSet<K> {
|
|
@Override
|
|
public Iterator<K> iterator() {
|
|
|
|
return new KeyIterator();
|
|
}
|
|
|
|
@Override
|
|
public int size() {
|
|
return ConcurrentWeakKeyHashMap.this.size();
|
|
}
|
|
|
|
@Override
|
|
public boolean isEmpty() {
|
|
return ConcurrentWeakKeyHashMap.this.isEmpty();
|
|
}
|
|
|
|
@Override
|
|
public boolean contains(Object o) {
|
|
return ConcurrentWeakKeyHashMap.this.containsKey(o);
|
|
}
|
|
|
|
@Override
|
|
public boolean remove(Object o) {
|
|
return ConcurrentWeakKeyHashMap.this.remove(o) != null;
|
|
|
|
}
|
|
|
|
@Override
|
|
public void clear() {
|
|
ConcurrentWeakKeyHashMap.this.clear();
|
|
}
|
|
}
|
|
|
|
final class Values extends AbstractCollection<V> {
|
|
@Override
|
|
public Iterator<V> iterator() {
|
|
return new ValueIterator();
|
|
}
|
|
|
|
@Override
|
|
public int size() {
|
|
return ConcurrentWeakKeyHashMap.this.size();
|
|
}
|
|
|
|
@Override
|
|
public boolean isEmpty() {
|
|
return ConcurrentWeakKeyHashMap.this.isEmpty();
|
|
}
|
|
|
|
@Override
|
|
public boolean contains(Object o) {
|
|
return ConcurrentWeakKeyHashMap.this.containsValue(o);
|
|
}
|
|
|
|
@Override
|
|
public void clear() {
|
|
ConcurrentWeakKeyHashMap.this.clear();
|
|
}
|
|
}
|
|
|
|
final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
|
|
@Override
|
|
public Iterator<Map.Entry<K, V>> iterator() {
|
|
return new EntryIterator();
|
|
}
|
|
|
|
@Override
|
|
public boolean contains(Object o) {
|
|
if (!(o instanceof Map.Entry<?, ?>)) {
|
|
return false;
|
|
}
|
|
Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
|
|
V v = ConcurrentWeakKeyHashMap.this.get(e.getKey());
|
|
return v != null && v.equals(e.getValue());
|
|
}
|
|
|
|
@Override
|
|
public boolean remove(Object o) {
|
|
if (!(o instanceof Map.Entry<?, ?>)) {
|
|
return false;
|
|
}
|
|
Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
|
|
return ConcurrentWeakKeyHashMap.this.remove(e.getKey(), e.getValue());
|
|
}
|
|
|
|
@Override
|
|
public int size() {
|
|
return ConcurrentWeakKeyHashMap.this.size();
|
|
}
|
|
|
|
@Override
|
|
public boolean isEmpty() {
|
|
return ConcurrentWeakKeyHashMap.this.isEmpty();
|
|
}
|
|
|
|
@Override
|
|
public void clear() {
|
|
ConcurrentWeakKeyHashMap.this.clear();
|
|
}
|
|
}
|
|
}
|