Many resources are needed to download a project. Please understand that we have to compensate our server costs. Thank you in advance.
Project price only 1 $
You can buy this project and download/modify it how often you want.
org.apache.commons.collections4.map.ConcurrentReferenceHashMap Maven / Gradle / Ivy
The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
* Copyright (c) 2008-2020, Hazelcast, Inc. All Rights Reserved.
*/
package org.apache.commons.collections4.map;
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.EnumSet;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* An advanced hash map supporting configurable garbage collection semantics of keys and values, optional referential-equality, full concurrency of retrievals,
* and adjustable expected concurrency for updates.
*
* This map is designed around specific advanced use-cases. If there is any doubt whether this map is for you, you most likely should be using
* {@link java.util.concurrent.ConcurrentHashMap} instead.
*
*
* This map supports strong, weak, and soft keys and values. By default, keys are weak, and values are strong. Such a configuration offers similar behavior to
* {@link java.util.WeakHashMap}, entries of this map are periodically removed once their corresponding keys are no longer referenced outside of this map. In
* other words, this map will not prevent a key from being discarded by the garbage collector. Once a key has been discarded by the collector, the corresponding
* entry is no longer visible to this map; however, the entry may occupy space until a future map operation decides to reclaim it. For this reason, summary
* functions such as {@code size} and {@code isEmpty} might return a value greater than the observed number of entries. In order to support a high level of
* concurrency, stale entries are only reclaimed during blocking (usually mutating) operations.
*
*
* Enabling soft keys allows entries in this map to remain until their space is absolutely needed by the garbage collector. This is unlike weak keys which can
* be reclaimed as soon as they are no longer referenced by a normal strong reference. The primary use case for soft keys is a cache, which ideally occupies
* memory that is not in use for as long as possible.
*
*
* By default, values are held using a normal strong reference. This provides the commonly desired guarantee that a value will always have at least the same
* life-span as its key. For this reason, care should be taken to ensure that a value never refers, either directly or indirectly, to its key, thereby
* preventing reclamation. If this is unavoidable, then it is recommended to use the same reference type in use for the key. However, it should be noted that
* non-strong values may disappear before their corresponding key.
*
*
* While this map does allow the use of both strong keys and values, it is recommended you use {@link java.util.concurrent.ConcurrentHashMap} for such a
* configuration, since it is optimized for that case.
*
*
* Just like {@link java.util.concurrent.ConcurrentHashMap}, this class obeys the same functional specification as {@link Hashtable}, and includes versions of
* methods corresponding to each method of {@code Hashtable}. However, even though all operations are thread-safe, retrieval operations do not entail
* locking, and there is not any support for locking the entire map in a way that prevents all access. This class is fully interoperable with
* {@code Hashtable} in programs that rely on its thread safety but not on its synchronization details.
*
*
* Retrieval operations (including {@code get}) generally do not block, so they may overlap with update operations (including {@code put} and {@code remove}).
* Retrievals reflect the results of the most recently completed update operations holding upon their onset. For aggregate operations such as
* {@code putAll} and {@code clear}, concurrent retrievals may reflect insertion or removal of only some entries. Similarly, Iterators and Enumerations return
* elements reflecting the state of the hash map at some point at or since the creation of the iterator/enumeration. They do not throw
* {@link ConcurrentModificationException}. However, iterators are designed to be used by only one thread at a time.
*
*
* The allowed concurrency among update operations is guided by the optional {@code concurrencyLevel} constructor argument (default
* {@value #DEFAULT_CONCURRENCY_LEVEL}), which is used as a hint for internal sizing. The map is internally partitioned to try to permit the indicated number of
* concurrent updates without contention. Because placement in hash tables is essentially random, the actual concurrency will vary. Ideally, you should choose a
* value to accommodate as many threads as will ever concurrently modify the map. Using a significantly higher value than you need can waste space and time, and
* a significantly lower value can lead to thread contention. But overestimates and underestimates within an order of magnitude do not usually have much
* noticeable impact. A value of one is appropriate when it is known that only one thread will modify and all others will only read. Also, resizing this or any
* other kind of hash map is a relatively slow operation, so, when possible, it is a good idea that you provide estimates of expected map sizes in constructors.
*
*
* This class and its views and iterators implement all of the optional methods of the {@link Map} and {@link Iterator} interfaces.
*
*
* Like {@link Hashtable} but unlike {@link HashMap}, this class does not allow {@code null} to be used as a key or value.
*
*
* Provenance: Copied and edited from Apache Groovy git master at commit 77dc80a7512ceb2168b1bc866c3d0c69b002fe11; via Doug Lea, Jason T. Greene, with
* assistance from members of JCP JSR-166, and Hazelcast.
*
*
* @param the type of keys maintained by this map.
* @param the type of mapped values.
*/
public class ConcurrentReferenceHashMap extends AbstractMap implements ConcurrentMap {
/**
* Builds new ConcurrentReferenceHashMap instances.
*
* By default, keys are weak, and values are strong.
*
*
* The default values are:
*
*
* concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}
* initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}
* key reference type: {@link ReferenceType#WEAK}
* load factor: {@value #DEFAULT_LOAD_FACTOR}
* options: {@code null}
* source map: {@code null}
* value reference type: {@link ReferenceType#STRONG}
*
*
* @param the type of keys.
* @param the type of values.
*/
public static class Builder implements Supplier> {
private static final Map DEFAULT_SOURCE_MAP = null;
private int initialCapacity = DEFAULT_INITIAL_CAPACITY;
private float loadFactor = DEFAULT_LOAD_FACTOR;
private int concurrencyLevel = DEFAULT_CONCURRENCY_LEVEL;
private ReferenceType keyReferenceType = DEFAULT_KEY_TYPE;
private ReferenceType valueReferenceType = DEFAULT_VALUE_TYPE;
private EnumSet options = DEFAULT_OPTIONS;
@SuppressWarnings("unchecked")
private Map sourceMap = (Map) DEFAULT_SOURCE_MAP;
/**
* Constructs a new instances of {@link ConcurrentReferenceHashMap}.
*/
public Builder() {
// empty
}
/**
* Builds a new {@link ConcurrentReferenceHashMap}.
*
* By default, keys are weak, and values are strong.
*
*
* The default values are:
*
*
* concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}
* initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}
* key reference type: {@link ReferenceType#WEAK}
* load factor: {@value #DEFAULT_LOAD_FACTOR}
* options: {@code null}
* source map: {@code null}
* value reference type: {@link ReferenceType#STRONG}
*
*/
@Override
public ConcurrentReferenceHashMap get() {
final ConcurrentReferenceHashMap map = new ConcurrentReferenceHashMap<>(initialCapacity, loadFactor, concurrencyLevel, keyReferenceType,
valueReferenceType, options);
if (sourceMap != null) {
map.putAll(sourceMap);
}
return map;
}
/**
* Sets the estimated number of concurrently updating threads. The implementation performs internal sizing to try to accommodate this many threads.
*
* @param concurrencyLevel estimated number of concurrently updating threads
* @return this instance.
*/
public Builder setConcurrencyLevel(final int concurrencyLevel) {
this.concurrencyLevel = concurrencyLevel;
return this;
}
/**
* Sets the initial capacity. The implementation performs internal sizing to accommodate this many elements.
*
* @param initialCapacity the initial capacity.
* @return this instance.
*/
public Builder setInitialCapacity(final int initialCapacity) {
this.initialCapacity = initialCapacity;
return this;
}
/**
* Sets the reference type to use for keys.
*
* @param keyReferenceType the reference type to use for keys.
* @return this instance.
*/
public Builder setKeyReferenceType(final ReferenceType keyReferenceType) {
this.keyReferenceType = keyReferenceType;
return this;
}
/**
* Sets the load factor factor, used to control resizing. Resizing may be performed when the average number of elements per bin exceeds this threshold.
*
* @param loadFactor the load factor factor, used to control resizing
* @return this instance.
*/
public Builder setLoadFactor(final float loadFactor) {
this.loadFactor = loadFactor;
return this;
}
/**
* Sets the behavioral options.
*
* @param options the behavioral options.
* @return this instance.
*/
public Builder setOptions(final EnumSet options) {
this.options = options;
return this;
}
/**
* Sets the values to load into a new map.
*
* @param sourceMap the values to load into a new map.
* @return this instance.
*/
public Builder setSourceMap(final Map sourceMap) {
this.sourceMap = sourceMap;
return this;
}
/**
* Sets the reference type to use for values.
*
* @param valueReferenceType the reference type to use for values.
* @return this instance.
*/
public Builder setValueReferenceType(final ReferenceType valueReferenceType) {
this.valueReferenceType = valueReferenceType;
return this;
}
/**
* Sets key reference type to {@link ReferenceType#SOFT}.
*
* @return this instance.
*/
public Builder softKeys() {
setKeyReferenceType(ReferenceType.SOFT);
return this;
}
/**
* Sets value reference type to {@link ReferenceType#SOFT}.
*
* @return this instance.
*/
public Builder softValues() {
setValueReferenceType(ReferenceType.SOFT);
return this;
}
/**
* Sets key reference type to {@link ReferenceType#STRONG}.
*
* @return this instance.
*/
public Builder strongKeys() {
setKeyReferenceType(ReferenceType.STRONG);
return this;
}
/**
* Sets value reference type to {@link ReferenceType#STRONG}.
*
* @return this instance.
*/
public Builder strongValues() {
setValueReferenceType(ReferenceType.STRONG);
return this;
}
/**
* Sets key reference type to {@link ReferenceType#WEAK}.
*
* @return this instance.
*/
public Builder weakKeys() {
setKeyReferenceType(ReferenceType.WEAK);
return this;
}
/**
* Sets value reference type to {@link ReferenceType#WEAK}.
*
* @return this instance.
*/
public Builder weakValues() {
setValueReferenceType(ReferenceType.WEAK);
return this;
}
}
/**
* The basic strategy is to subdivide the table among Segments, each of which itself is a concurrently readable hash table.
*/
private final class CachedEntryIterator extends HashIterator implements Iterator> {
private final InitializableEntry entry = new InitializableEntry<>();
@Override
public Entry next() {
final HashEntry e = super.nextEntry();
return entry.init(e.key(), e.value());
}
}
private final class EntryIterator extends HashIterator implements Iterator> {
@Override
public Entry next() {
final HashEntry e = super.nextEntry();
return new WriteThroughEntry(e.key(), e.value());
}
}
private final class EntrySet extends AbstractSet> {
private final boolean cached;
private EntrySet(final boolean cached) {
this.cached = cached;
}
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
@Override
public boolean contains(final Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final V v = ConcurrentReferenceHashMap.this.get(((Entry) o).getKey());
return Objects.equals(v, ((Entry) o).getValue());
}
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
@Override
public Iterator> iterator() {
return cached ? new CachedEntryIterator() : new EntryIterator();
}
@Override
public boolean remove(final Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final Entry e = (Entry) o;
return ConcurrentReferenceHashMap.this.remove(e.getKey(), e.getValue());
}
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
}
/**
* ConcurrentReferenceHashMap list entry. Note that this is never exported out as a user-visible Map.Entry.
*
* Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an unsynchronized reader to see null instead of initial value
* when read via a data race. Although a reordering leading to this is not likely to ever actually occur, the Segment.readValueUnderLock method is used as a
* backup in case a null (pre-initialized) value is ever seen in an unsynchronized access method.
*
*/
private static final class HashEntry {
@SuppressWarnings("unchecked")
static HashEntry[] newArray(final int i) {
return new HashEntry[i];
}
private final Object keyRef;
private final int hash;
private volatile Object valueRef;
private final HashEntry next;
HashEntry(final K key, final int hash, final HashEntry next, final V value, final ReferenceType keyType, final ReferenceType valueType,
final ReferenceQueue refQueue) {
this.hash = hash;
this.next = next;
this.keyRef = newKeyReference(key, keyType, refQueue);
this.valueRef = newValueReference(value, valueType, refQueue);
}
@SuppressWarnings("unchecked")
V dereferenceValue(final Object value) {
if (value instanceof KeyReference) {
return ((Reference) value).get();
}
return (V) value;
}
@SuppressWarnings("unchecked")
K key() {
if (keyRef instanceof KeyReference) {
return ((Reference) keyRef).get();
}
return (K) keyRef;
}
Object newKeyReference(final K key, final ReferenceType keyType, final ReferenceQueue refQueue) {
if (keyType == ReferenceType.WEAK) {
return new WeakKeyReference<>(key, hash, refQueue);
}
if (keyType == ReferenceType.SOFT) {
return new SoftKeyReference<>(key, hash, refQueue);
}
return key;
}
Object newValueReference(final V value, final ReferenceType valueType, final ReferenceQueue refQueue) {
if (valueType == ReferenceType.WEAK) {
return new WeakValueReference<>(value, keyRef, hash, refQueue);
}
if (valueType == ReferenceType.SOFT) {
return new SoftValueReference<>(value, keyRef, hash, refQueue);
}
return value;
}
void setValue(final V value, final ReferenceType valueType, final ReferenceQueue refQueue) {
this.valueRef = newValueReference(value, valueType, refQueue);
}
V value() {
return dereferenceValue(valueRef);
}
}
private abstract class HashIterator {
private int nextSegmentIndex;
private int nextTableIndex;
private HashEntry[] currentTable;
private HashEntry nextEntry;
private HashEntry lastReturned;
// Strong reference to weak key (prevents gc)
private K currentKey;
private HashIterator() {
nextSegmentIndex = segments.length - 1;
nextTableIndex = -1;
advance();
}
final void advance() {
if (nextEntry != null && (nextEntry = nextEntry.next) != null) {
return;
}
while (nextTableIndex >= 0) {
if ((nextEntry = currentTable[nextTableIndex--]) != null) {
return;
}
}
while (nextSegmentIndex >= 0) {
final Segment 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 hasMoreElements() {
return hasNext();
}
public boolean hasNext() {
while (nextEntry != null) {
if (nextEntry.key() != null) {
return true;
}
advance();
}
return false;
}
HashEntry nextEntry() {
do {
if (nextEntry == null) {
throw new NoSuchElementException();
}
lastReturned = nextEntry;
currentKey = lastReturned.key();
advance();
} while /* Skip GC'd keys */ (currentKey == null);
return lastReturned;
}
public void remove() {
if (lastReturned == null) {
throw new IllegalStateException();
}
ConcurrentReferenceHashMap.this.remove(currentKey);
lastReturned = null;
}
}
private static final class InitializableEntry implements Entry {
private K key;
private V value;
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
public Entry init(final K key, final V value) {
this.key = key;
this.value = value;
return this;
}
@Override
public V setValue(final V value) {
throw new UnsupportedOperationException();
}
}
private final class KeyIterator extends HashIterator implements Iterator, Enumeration {
@Override
public K next() {
return super.nextEntry().key();
}
@Override
public K nextElement() {
return super.nextEntry().key();
}
}
private interface KeyReference {
int keyHash();
Object keyRef();
}
private final class KeySet extends AbstractSet {
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
@Override
public boolean contains(final Object o) {
return ConcurrentReferenceHashMap.this.containsKey(o);
}
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
@Override
public Iterator iterator() {
return new KeyIterator();
}
@Override
public boolean remove(final Object o) {
return ConcurrentReferenceHashMap.this.remove(o) != null;
}
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
}
/**
* Behavior-changing configuration options for the map
*/
public enum Option {
/**
* Indicates that referential-equality (== instead of .equals()) should be used when locating keys. This offers similar behavior to
* {@link IdentityHashMap}
*/
IDENTITY_COMPARISONS
}
/**
* An option specifying which Java reference type should be used to refer to a key and/or value.
*/
public enum ReferenceType {
/**
* Indicates a normal Java strong reference should be used
*/
STRONG,
/**
* Indicates a {@link WeakReference} should be used
*/
WEAK,
/**
* Indicates a {@link SoftReference} should be used
*/
SOFT
}
/**
* Segments are specialized versions of hash tables. This subclasses from ReentrantLock opportunistically, just to simplify some locking and avoid separate
* construction.
*
* Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so they can be read without locking. Next fields of nodes are
* immutable (final). All list additions are performed at the front of each bin. This makes it easy to check changes, and also fast to traverse. When nodes
* would otherwise be changed, new nodes are created to replace them. This works well for hash tables since the bin lists tend to be short. (The average
* length is less than two for the default load factor threshold.)
*
*
* Read operations can thus proceed without locking, but rely on selected uses of volatiles to ensure that completed write operations performed by other
* threads are noticed. For most purposes, the "count" field, tracking the number of elements, serves as that volatile variable ensuring visibility. This is
* convenient because this field needs to be read in many read operations anyway:
*
*
* All (unsynchronized) read operations must first read the "count" field, and should not look at table entries if it is 0.
* All (synchronized) write operations should write to the "count" field after structurally changing any bin. The operations must not take any action
* that could even momentarily cause a concurrent read operation to see inconsistent data. This is made easier by the nature of the read operations in Map.
* For example, no operation can reveal that the table has grown but the threshold has not yet been updated, so there are no atomicity requirements for this
* with respect to reads.
*
*
* As a guide, all critical volatile reads and writes to the count field are marked in code comments.
*
*
* @param the type of keys maintained by this Segment.
* @param the type of mapped values.
*/
private static final class Segment extends ReentrantLock {
private static final long serialVersionUID = 1L;
@SuppressWarnings("unchecked")
static Segment[] newArray(final int i) {
return new Segment[i];
}
/**
* The number of elements in this segment's region.
*/
// @SuppressFBWarnings(value = "SE_TRANSIENT_FIELD_NOT_RESTORED", justification =
// "I trust Doug Lea's technical decision")
private transient volatile int count;
/**
* Number of updates that alter the size of the table. This is used during bulk-read methods to make sure they see a consistent snapshot: If modCounts
* change during a traversal of segments computing size or checking containsValue, then we might have an inconsistent view of state so (usually) we must
* retry.
*/
// @SuppressFBWarnings(value = "SE_TRANSIENT_FIELD_NOT_RESTORED", justification =
// "I trust Doug Lea's technical decision")
private transient int modCount;
/**
* The table is rehashed when its size exceeds this threshold. (The value of this field is always (int)(capacity *
* loadFactor).)
*/
private transient int threshold;
/**
* The per-segment table.
*/
private transient volatile HashEntry[] table;
/**
* The load factor for the hash table. Even though this value is same for all segments, it is replicated to avoid needing links to outer object.
*/
private final float loadFactor;
/**
* The collected weak-key reference queue for this segment. This should be (re)initialized whenever table is assigned,
*/
private transient volatile ReferenceQueue refQueue;
private final ReferenceType keyType;
private final ReferenceType valueType;
private final boolean identityComparisons;
Segment(final int initialCapacity, final float loadFactor, final ReferenceType keyType, final ReferenceType valueType,
final boolean identityComparisons) {
this.loadFactor = loadFactor;
this.keyType = keyType;
this.valueType = valueType;
this.identityComparisons = identityComparisons;
setTable(HashEntry.newArray(initialCapacity));
}
V apply(final K key, final int hash, final BiFunction remappingFunction) {
lock();
try {
final V oldValue = get(key, hash);
final V newValue = remappingFunction.apply(key, oldValue);
if (newValue == null) {
// delete mapping
if (oldValue != null) {
// something to remove
removeInternal(key, hash, oldValue, false);
}
return null;
}
// add or replace old mapping
putInternal(key, hash, newValue, null, false);
return newValue;
} finally {
unlock();
}
}
V applyIfPresent(final K key, final int hash, final BiFunction remappingFunction) {
lock();
try {
final V oldValue = get(key, hash);
if (oldValue == null) {
return null;
}
final V newValue = remappingFunction.apply(key, oldValue);
if (newValue == null) {
removeInternal(key, hash, oldValue, false);
return null;
}
putInternal(key, hash, newValue, null, false);
return newValue;
} finally {
unlock();
}
}
void clear() {
if (count != 0) {
lock();
try {
final HashEntry[] tab = table;
Arrays.fill(tab, null);
++modCount;
// replace the reference queue to avoid unnecessary stale cleanups
refQueue = new ReferenceQueue<>();
// write-volatile
count = 0;
} finally {
unlock();
}
}
}
boolean containsKey(final Object key, final int hash) {
// read-volatile
if (count != 0) {
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && keyEq(key, e.key())) {
return true;
}
e = e.next;
}
}
return false;
}
boolean containsValue(final Object value) {
// read-volatile
if (count != 0) {
final HashEntry[] tab = table;
final int len = tab.length;
for (int i = 0; i < len; i++) {
for (HashEntry e = tab[i]; e != null; e = e.next) {
final Object opaque = e.valueRef;
final V v;
if (opaque == null) {
// recheck
v = readValueUnderLock(e);
} else {
v = e.dereferenceValue(opaque);
}
if (Objects.equals(value, v)) {
return true;
}
}
}
}
return false;
}
/* Specialized implementations of map methods */
V get(final Object key, final int hash) {
// read-volatile
if (count != 0) {
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && keyEq(key, e.key())) {
final Object opaque = e.valueRef;
if (opaque != null) {
return e.dereferenceValue(opaque);
}
// recheck
return readValueUnderLock(e);
}
e = e.next;
}
}
return null;
}
/**
* Gets properly casted first entry of bin for given hash.
*/
HashEntry getFirst(final int hash) {
final HashEntry[] tab = table;
return tab[hash & tab.length - 1];
}
V getValue(final K key, final V value, final Function function) {
return value != null ? value : function.apply(key);
}
private boolean keyEq(final Object src, final Object dest) {
return identityComparisons ? src == dest : Objects.equals(src, dest);
}
HashEntry newHashEntry(final K key, final int hash, final HashEntry next, final V value) {
return new HashEntry<>(key, hash, next, value, keyType, valueType, refQueue);
}
/**
* This method must be called with exactly one of value and function non-null.
**/
V put(final K key, final int hash, final V value, final Function function, final boolean onlyIfAbsent) {
lock();
try {
return putInternal(key, hash, value, function, onlyIfAbsent);
} finally {
unlock();
}
}
private V putInternal(final K key, final int hash, final V value, final Function function, final boolean onlyIfAbsent) {
removeStale();
int c = count;
// ensure capacity
if (c++ > threshold) {
final int reduced = rehash();
// adjust from possible weak cleanups
if (reduced > 0) {
// write-volatile
count = (c -= reduced) - 1;
}
}
final HashEntry[] tab = table;
final int index = hash & tab.length - 1;
final HashEntry first = tab[index];
HashEntry e = first;
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
final V resultValue;
if (e != null) {
resultValue = e.value();
if (!onlyIfAbsent) {
e.setValue(getValue(key, value, function), valueType, refQueue);
}
} else {
final V v = getValue(key, value, function);
resultValue = function != null ? v : null;
if (v != null) {
++modCount;
tab[index] = newHashEntry(key, hash, first, v);
// write-volatile
count = c;
}
}
return resultValue;
}
/**
* Reads value field of an entry under lock. Called if value field ever appears to be null. This is possible only if a compiler happens to reorder a
* HashEntry initialization with its table assignment, which is legal under memory model but is not known to ever occur.
*/
V readValueUnderLock(final HashEntry e) {
lock();
try {
removeStale();
return e.value();
} finally {
unlock();
}
}
int rehash() {
final HashEntry[] oldTable = table;
final int oldCapacity = oldTable.length;
if (oldCapacity >= MAXIMUM_CAPACITY) {
return 0;
}
//
// Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the elements from each bin must either stay at the same
// index, or move with a power of two offset. We eliminate unnecessary node creation by catching cases where old nodes can be reused because their
// next fields won't change. Statistically, at the default threshold, only about one-sixth of them need cloning when a table doubles. The nodes they
// replace will be garbage collectable as soon as they are no longer referenced by any reader thread that may be in the midst of traversing table
// right now.
//
final HashEntry[] newTable = HashEntry.newArray(oldCapacity << 1);
threshold = (int) (newTable.length * loadFactor);
final int sizeMask = newTable.length - 1;
int reduce = 0;
for (int i = 0; i < oldCapacity; i++) {
// We need to guarantee that any existing reads of old Map can
// proceed. So we cannot yet null out each bin.
final HashEntry e = oldTable[i];
if (e != null) {
final HashEntry next = e.next;
final int idx = e.hash & sizeMask;
// Single node on list
if (next == null) {
newTable[idx] = e;
} else {
// Reuse trailing consecutive sequence at same slot
HashEntry lastRun = e;
int lastIdx = idx;
for (HashEntry last = next; last != null; last = last.next) {
final int k = last.hash & sizeMask;
if (k != lastIdx) {
lastIdx = k;
lastRun = last;
}
}
newTable[lastIdx] = lastRun;
// Clone all remaining nodes
for (HashEntry p = e; p != lastRun; p = p.next) {
// Skip GC'd weak refs
final K key = p.key();
if (key == null) {
reduce++;
continue;
}
final int k = p.hash & sizeMask;
final HashEntry n = newTable[k];
newTable[k] = newHashEntry(key, p.hash, n, p.value());
}
}
}
}
table = newTable;
return reduce;
}
/**
* Removes match on key only if value is null, else match both.
*/
V remove(final Object key, final int hash, final Object value, final boolean refRemove) {
lock();
try {
return removeInternal(key, hash, value, refRemove);
} finally {
unlock();
}
}
private V removeInternal(final Object key, final int hash, final Object value, final boolean refRemove) {
if (!refRemove) {
removeStale();
}
int c = count - 1;
final HashEntry[] tab = table;
final int index = hash & tab.length - 1;
final HashEntry first = tab[index];
HashEntry e = first;
// a ref 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) {
final 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 newFirst = e.next;
for (HashEntry p = first; p != e; p = p.next) {
final K pKey = p.key();
// Skip GC'd keys
if (pKey == null) {
c--;
continue;
}
newFirst = newHashEntry(pKey, p.hash, newFirst, p.value());
}
tab[index] = newFirst;
// write-volatile
count = c;
}
}
return oldValue;
}
void removeStale() {
KeyReference ref;
while ((ref = (KeyReference) refQueue.poll()) != null) {
remove(ref.keyRef(), ref.keyHash(), null, true);
}
}
V replace(final K key, final int hash, final V newValue) {
lock();
try {
return replaceInternal(key, hash, newValue);
} finally {
unlock();
}
}
boolean replace(final K key, final int hash, final V oldValue, final V newValue) {
lock();
try {
return replaceInternal2(key, hash, oldValue, newValue);
} finally {
unlock();
}
}
private V replaceInternal(final K key, final int hash, final V newValue) {
removeStale();
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
V oldValue = null;
if (e != null) {
oldValue = e.value();
e.setValue(newValue, valueType, refQueue);
}
return oldValue;
}
private boolean replaceInternal2(final K key, final int hash, final V oldValue, final V newValue) {
removeStale();
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
boolean replaced = false;
if (e != null && Objects.equals(oldValue, e.value())) {
replaced = true;
e.setValue(newValue, valueType, refQueue);
}
return replaced;
}
/**
* Sets table to new HashEntry array. Call only while holding lock or in constructor.
*/
void setTable(final HashEntry[] newTable) {
threshold = (int) (newTable.length * loadFactor);
table = newTable;
refQueue = new ReferenceQueue<>();
}
}
private static class SimpleEntry implements Entry {
private static boolean eq(final Object o1, final Object o2) {
return Objects.equals(o1, o2);
}
private final K key;
private V value;
SimpleEntry(final K key, final V value) {
this.key = key;
this.value = value;
}
@Override
public boolean equals(final Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final Entry e = (Entry) o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public int hashCode() {
return (key == null ? 0 : key.hashCode()) ^ (value == null ? 0 : value.hashCode());
}
@Override
public V setValue(final V value) {
final V oldValue = this.value;
this.value = value;
return oldValue;
}
@Override
public String toString() {
return key + "=" + value;
}
}
/**
* A soft-key reference which stores the key hash needed for reclamation.
*/
private static final class SoftKeyReference extends SoftReference implements KeyReference {
private final int hash;
SoftKeyReference(final K key, final int hash, final ReferenceQueue refQueue) {
super(key, refQueue);
this.hash = hash;
}
@Override
public int keyHash() {
return hash;
}
@Override
public Object keyRef() {
return this;
}
}
private static final class SoftValueReference extends SoftReference implements KeyReference {
private final Object keyRef;
private final int hash;
SoftValueReference(final V value, final Object keyRef, final int hash, final ReferenceQueue refQueue) {
super(value, refQueue);
this.keyRef = keyRef;
this.hash = hash;
}
@Override
public int keyHash() {
return hash;
}
@Override
public Object keyRef() {
return keyRef;
}
}
private final class ValueIterator extends HashIterator implements Iterator, Enumeration {
@Override
public V next() {
return super.nextEntry().value();
}
@Override
public V nextElement() {
return super.nextEntry().value();
}
}
private final class Values extends AbstractCollection {
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
@Override
public boolean contains(final Object o) {
return ConcurrentReferenceHashMap.this.containsValue(o);
}
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
@Override
public Iterator iterator() {
return new ValueIterator();
}
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
}
/**
* A weak-key reference which stores the key hash needed for reclamation.
*/
private static final class WeakKeyReference extends WeakReference implements KeyReference {
private final int hash;
WeakKeyReference(final K key, final int hash, final ReferenceQueue refQueue) {
super(key, refQueue);
this.hash = hash;
}
@Override
public int keyHash() {
return hash;
}
@Override
public Object keyRef() {
return this;
}
}
private static final class WeakValueReference extends WeakReference implements KeyReference {
private final Object keyRef;
private final int hash;
WeakValueReference(final V value, final Object keyRef, final int hash, final ReferenceQueue refQueue) {
super(value, refQueue);
this.keyRef = keyRef;
this.hash = hash;
}
@Override
public int keyHash() {
return hash;
}
@Override
public Object keyRef() {
return keyRef;
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying map.
*/
private final class WriteThroughEntry extends SimpleEntry {
private WriteThroughEntry(final K k, final V v) {
super(k, v);
}
/**
* Set our entry's value and writes it through to the map. The value to return is somewhat arbitrary: 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 cannot guarantee more.
*/
@Override
public V setValue(final V value) {
Objects.requireNonNull(value, "value");
final V v = super.setValue(value);
ConcurrentReferenceHashMap.this.put(getKey(), value);
return v;
}
}
static final ReferenceType DEFAULT_KEY_TYPE = ReferenceType.WEAK;
static final ReferenceType DEFAULT_VALUE_TYPE = ReferenceType.STRONG;
static final EnumSet DEFAULT_OPTIONS = null;
/**
* The default initial capacity for this table, used when not otherwise specified in a constructor.
*/
static final int DEFAULT_INITIAL_CAPACITY = 16;
/**
* The default load factor for this table, used when not otherwise specified in a constructor.
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The default concurrency level for this table, used when not otherwise specified in a constructor.
*/
static final int DEFAULT_CONCURRENCY_LEVEL = 16;
/**
* The maximum capacity, used if a higher value is implicitly specified by either of the constructors with arguments. MUST be a power of two <=
* 1<<30 to ensure that entries are indexable using ints.
*/
private static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The maximum number of segments to allow; used to bound constructor arguments.
*/
private static final int MAX_SEGMENTS = 1 << 16;
/**
* Number of unsynchronized retries in size and containsValue methods before resorting to locking. This is used to avoid unbounded retries if tables undergo
* continuous modification which would make it impossible to obtain an accurate result.
*/
private static final int RETRIES_BEFORE_LOCK = 2;
/**
* Creates a new Builder.
*
* By default, keys are weak, and values are strong.
*
*
* The default values are:
*
*
* concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}
* initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}
* key reference type: {@link ReferenceType#WEAK}
* load factor: {@value #DEFAULT_LOAD_FACTOR}
* options: {@code null}
* source map: {@code null}
* value reference type: {@link ReferenceType#STRONG}
*
*
* @param the type of keys.
* @param the type of values.
* @return a new Builder.
*/
public static Builder builder() {
return new Builder<>();
}
/**
* Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions. This is critical because
* ConcurrentReferenceHashMap uses power-of-two length hash tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper
* bits.
*/
private static int hash(int h) {
// Spread bits to regularize both segment and index locations,
// using variant of single-word Wang/Jenkins hash.
h += h << 15 ^ 0xffffcd7d;
h ^= h >>> 10;
h += h << 3;
h ^= h >>> 6;
h += (h << 2) + (h << 14);
return h ^ h >>> 16;
}
/**
* Mask value for indexing into segments. The upper bits of a key's hash code are used to choose the segment.
*/
private final int segmentMask;
/**
* Shift value for indexing within segments.
*/
private final int segmentShift;
/**
* The segments, each of which is a specialized hash table
*/
private final Segment[] segments;
private final boolean identityComparisons;
private transient Set keySet;
private transient Set> entrySet;
private transient Collection values;
/**
* Creates a new, empty map with the specified initial capacity, reference types, load factor, and concurrency level.
*
* Behavioral changing options such as {@link Option#IDENTITY_COMPARISONS} can also be specified.
*
*
* @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.
* @param keyType the reference type to use for keys.
* @param valueType the reference type to use for values.
* @param options the behavioral options.
* @throws IllegalArgumentException if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
*/
private ConcurrentReferenceHashMap(int initialCapacity, final float loadFactor, int concurrencyLevel, final ReferenceType keyType,
final ReferenceType valueType, final EnumSet options) {
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;
}
identityComparisons = options != null && options.contains(Option.IDENTITY_COMPARISONS);
for (int i = 0; i < this.segments.length; ++i) {
this.segments[i] = new Segment<>(cap, loadFactor, keyType, valueType, identityComparisons);
}
}
/**
* Removes all of the mappings from this map.
*/
@Override
public void clear() {
for (final Segment segment : segments) {
segment.clear();
}
}
@Override
public V compute(final K key, final BiFunction remappingFunction) {
Objects.requireNonNull(key);
Objects.requireNonNull(remappingFunction);
final int hash = hashOf(key);
final Segment segment = segmentFor(hash);
return segment.apply(key, hash, remappingFunction);
}
/**
* The default implementation is equivalent to the following steps for this {@code map}, then returning the current value or {@code null} if now absent:
*
* {@code
* if (map.get(key) == null) {
* V newValue = mappingFunction.apply(key);
* if (newValue != null)
* return map.putIfAbsent(key, newValue);
* }
* }
*
* The default implementation may retry these steps when multiple threads attempt updates including potentially calling the mapping function multiple times.
*
*
* This implementation assumes that the ConcurrentMap cannot contain null values and {@code get()} returning null unambiguously means the key is absent.
* Implementations which support null values must override this default implementation.
*
*/
@Override
public V computeIfAbsent(final K key, final Function mappingFunction) {
Objects.requireNonNull(key);
Objects.requireNonNull(mappingFunction);
final int hash = hashOf(key);
final Segment segment = segmentFor(hash);
final V v = segment.get(key, hash);
return v == null ? segment.put(key, hash, null, mappingFunction, true) : v;
}
@Override
public V computeIfPresent(final K key, final BiFunction remappingFunction) {
Objects.requireNonNull(key);
Objects.requireNonNull(remappingFunction);
final int hash = hashOf(key);
final Segment segment = segmentFor(hash);
final V v = segment.get(key, hash);
if (v == null) {
return null;
}
return segmentFor(hash).applyIfPresent(key, hash, remappingFunction);
}
/**
* Tests if the specified object is a key in this table.
*
* @param key possible key
* @return {@code true} if and only if the specified object is a key in this table, as determined by the {@code equals} method; {@code false} otherwise.
* @throws NullPointerException if the specified key is null
*/
@Override
public boolean containsKey(final Object key) {
final int hash = hashOf(key);
return segmentFor(hash).containsKey(key, hash);
}
/**
* Returns {@code true} if this map maps one or more keys to the specified value. Note: This method requires a full internal traversal of the hash table,
* therefore it is much slower than the method {@code containsKey}.
*
* @param value value whose presence in this map is to be tested
* @return {@code true} if this map maps one or more keys to the specified value
* @throws NullPointerException if the specified value is null
*/
@Override
public boolean containsValue(final Object value) {
Objects.requireNonNull(value, "value");
// See explanation of modCount use above
final Segment[] segments = this.segments;
final int[] mc = new int[segments.length];
// Try a few times without locking
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
// final int sum = 0;
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
// final int c = segments[i].count;
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) {
// final int c = segments[i].count;
if (mc[i] != segments[i].modCount) {
cleanSweep = false;
break;
}
}
}
if (cleanSweep) {
return false;
}
}
// Resort to locking all segments
for (final Segment segment : segments) {
segment.lock();
}
boolean found = false;
try {
for (final Segment segment : segments) {
if (segment.containsValue(value)) {
found = true;
break;
}
}
} finally {
for (final Segment segment : segments) {
segment.unlock();
}
}
return found;
}
/**
* 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 {@code Iterator.remove}, {@code Set.remove},
* {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the {@code add} or {@code addAll} operations.
*
* The view's {@code iterator} is a "weakly consistent" iterator that will never throw {@link ConcurrentModificationException}, and is guaranteed 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> entrySet() {
final Set> es = entrySet;
return es != null ? es : (entrySet = new EntrySet(false));
}
/**
* Gets the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.
*
* 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(final Object key) {
final int hash = hashOf(key);
return segmentFor(hash).get(key, hash);
}
private int hashOf(final Object key) {
return hash(identityComparisons ? System.identityHashCode(key) : key.hashCode());
}
/**
* Returns {@code true} if this map contains no key-value mappings.
*
* @return {@code true} if this map contains no key-value mappings
*/
@Override
public boolean isEmpty() {
final Segment[] 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.
//
final int[] mc = new int[segments.length];
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
if (segments[i].count != 0) {
return false;
}
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 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 {@code Iterator.remove}, {@code Set.remove},
* {@code removeAll}, {@code retainAll}, and {@code clear} operations. It does not support the {@code add} or {@code addAll} operations.
*
* The view's {@code iterator} 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 keySet() {
final Set ks = keySet;
return ks != null ? ks : (keySet = new KeySet());
}
/**
* 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 this method should be used sparingly.
*
*/
public void purgeStaleEntries() {
for (final Segment segment : segments) {
segment.removeStale();
}
}
/**
* Maps the specified key to the specified value in this table. Neither the key nor the value can be null.
*
* The value can be retrieved by calling the {@code get} 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 {@code key}, or {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V put(final K key, final V value) {
Objects.requireNonNull(key, "key");
Objects.requireNonNull(value, "value");
final int hash = hashOf(key);
return segmentFor(hash).put(key, hash, value, null, false);
}
/**
* 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(final Map m) {
for (final Entry e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V putIfAbsent(final K key, final V value) {
Objects.requireNonNull(value, "value");
final int hash = hashOf(key);
return segmentFor(hash).put(key, hash, value, null, true);
}
/**
* 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 {@code key}, or {@code null} if there was no mapping for {@code key}
* @throws NullPointerException if the specified key is null
*/
@Override
public V remove(final Object key) {
final 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(final Object key, final Object value) {
final int hash = hashOf(key);
if (value == null) {
return false;
}
return segmentFor(hash).remove(key, hash, value, false) != null;
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or {@code null} if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V replace(final K key, final V value) {
Objects.requireNonNull(value, "value");
final int hash = hashOf(key);
return segmentFor(hash).replace(key, hash, value);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if any of the arguments are null
*/
@Override
public boolean replace(final K key, final V oldValue, final V newValue) {
Objects.requireNonNull(oldValue, "oldValue");
Objects.requireNonNull(newValue, "newValue");
final int hash = hashOf(key);
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
* Returns the segment that should be used for key with given hash
*
* @param hash the hash code for the key
* @return the segment
*/
private Segment segmentFor(final int hash) {
return segments[hash >>> segmentShift & segmentMask];
}
/**
* Returns the number of key-value mappings in this map. If the map contains more than {@code Integer.MAX_VALUE} elements, returns
* {@code Integer.MAX_VALUE}.
*
* @return the number of key-value mappings in this map
*/
@Override
public int size() {
final Segment[] segments = this.segments;
long sum = 0;
long check = 0;
final 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) {
// force retry
check = -1;
break;
}
}
}
if (check == sum) {
break;
}
}
if (check != sum) {
// Resort to locking all segments
sum = 0;
for (final Segment segment : segments) {
segment.lock();
}
for (final Segment segment : segments) {
sum += segment.count;
}
for (final Segment segment : segments) {
segment.unlock();
}
}
return sum > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) sum;
}
/**
* 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
* {@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.
*
* The view's {@code iterator} 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 values() {
final Collection vs = values;
return vs != null ? vs : (values = new Values());
}
}
