This is an automated email from the ASF dual-hosted git repository.
ggregory pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-collections.git
The following commit(s) were added to refs/heads/master by this push:
new 0fa7d7323 Add Add ConcurrentReferenceHashMap
0fa7d7323 is described below
commit 0fa7d7323fc1d516fcb5fb7ae588cbb93341f6b8
Author: Gary Gregory <garydgreg...@gmail.com>
AuthorDate: Sat Sep 28 15:45:24 2024 -0400
Add Add ConcurrentReferenceHashMap
---
NOTICE.txt | 4 +
src/changes/changes.xml | 1 +
.../map/ConcurrentReferenceHashMap.java | 1885 ++++++++++++++++++++
.../AbstractConcurrentReferenceHashMapTest.java | 58 +
.../map/ConcurrentHashMapSanityTest.java | 63 +
.../ConcurrentReferenceHashMapDefaultsTest.java | 31 +
...oncurrentReferenceHashMapKSoftVSoftIdCTest.java | 35 +
.../ConcurrentReferenceHashMapKSoftVSoftTest.java | 34 +
...currentReferenceHashMapKSoftVStrongIdCTest.java | 35 +
...ConcurrentReferenceHashMapKSoftVStrongTest.java | 34 +
...oncurrentReferenceHashMapKSoftVWeakIdCTest.java | 35 +
.../ConcurrentReferenceHashMapKSoftVWeakTest.java | 34 +
...currentReferenceHashMapKStrongVSoftIdCTest.java | 35 +
...ConcurrentReferenceHashMapKStrongVSoftTest.java | 34 +
...rrentReferenceHashMapKStrongVStrongIdCTest.java | 35 +
...ncurrentReferenceHashMapKStrongVStrongTest.java | 35 +
...currentReferenceHashMapKStrongVWeakIdCTest.java | 35 +
...ConcurrentReferenceHashMapKStrongVWeakTest.java | 34 +
...oncurrentReferenceHashMapKWeakVSoftIdCTest.java | 35 +
.../ConcurrentReferenceHashMapKWeakVSoftTest.java | 35 +
...currentReferenceHashMapKWeakVStrongIdCTest.java | 35 +
...ConcurrentReferenceHashMapKWeakVStrongTest.java | 34 +
...oncurrentReferenceHashMapKWeakVWeakIdCTest.java | 35 +
.../ConcurrentReferenceHashMapKWeakVWeakTest.java | 34 +
.../map/ConcurrentReferenceHashMapTest.java | 55 +
25 files changed, 2720 insertions(+)
diff --git a/NOTICE.txt b/NOTICE.txt
index a5369e791..97b38fd63 100644
--- a/NOTICE.txt
+++ b/NOTICE.txt
@@ -3,3 +3,7 @@ Copyright 2001-2024 The Apache Software Foundation
This product includes software developed at
The Apache Software Foundation (https://www.apache.org/).
+
+The Java source file
src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
+is from https://github.com/hazelcast/hazelcast and the following notice
applies:
+Copyright (c) 2008-2020, Hazelcast, Inc. All Rights Reserved.
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index cb39c1d33..b30019ee5 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -44,6 +44,7 @@
<action type="add" dev="ggregory" due-to="Gary Gregory">Add
TreeBag.TreeBag(Iterable).</action>
<action type="add" issue="COLLECTIONS-858" dev="ggregory" due-to="Alexey
Pelykh, Alex Herbert, Gary Gregory">Add CartesianProductIterator #509.</action>
<action type="add" dev="ggregory" due-to="Gary Gregory">Add missing
methods in AbstractMapTests.</action>
+ <action type="add" dev="ggregory" due-to="Gary Gregory">Add
ConcurrentReferenceHashMap.</action>
<!-- UPDATE -->
<action type="update" issue="COLLECTIONS-857" dev="ggregory"
due-to="Claude Warren">Update bloom filter documentation #508.</action>
<action type="update" dev="ggregory" due-to="Dependabot, Gary
Gregory">Bump commons-codec:commons-codec from 1.17.0 to 1.17.1 #514.</action>
diff --git
a/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
b/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
new file mode 100644
index 000000000..74739d7b8
--- /dev/null
+++
b/src/main/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMap.java
@@ -0,0 +1,1885 @@
+/*
+ * 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.
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * 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 <em>not</em>
entail
+ * locking, and there is <em>not</em> 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.
+ * </p>
+ * <p>
+ * 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 <em>completed</em>
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 <em>not</em> throw
+ * {@link ConcurrentModificationException}. However, iterators are designed to
be used by only one thread at a time.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ * <p>
+ * This class and its views and iterators implement all of the
<em>optional</em> methods of the {@link Map} and {@link Iterator} interfaces.
+ * </p>
+ * <p>
+ * Like {@link Hashtable} but unlike {@link HashMap}, this class does
<em>not</em> allow {@code null} to be used as a key or value.
+ * </p>
+ * <p>
+ * 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.
+ * </p>
+ *
+ * @param <K> the type of keys maintained by this map.
+ * @param <V> the type of mapped values.
+ */
+public class ConcurrentReferenceHashMap<K, V> extends AbstractMap<K, V>
implements ConcurrentMap<K, V> {
+
+ /**
+ * Builds new ConcurrentReferenceHashMap instances.
+ * <p>
+ * By default, keys are weak, and values are strong.
+ * </p>
+ * <p>
+ * The default values are:
+ * </p>
+ * <ul>
+ * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+ * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+ * <li>key reference type: {@link ReferenceType#WEAK}</li>
+ * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+ * <li>options: {@code null}</li>
+ * <li>source map: {@code null}</li>
+ * <li>value reference type: {@link ReferenceType#STRONG}</li>
+ * </ul>
+ *
+ * @param <K> the type of keys.
+ * @param <V> the type of values.
+ */
+ public static class Builder<K, V> implements
Supplier<ConcurrentReferenceHashMap<K, V>> {
+
+ 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<Option> options = DEFAULT_OPTIONS;
+ @SuppressWarnings("unchecked")
+ private Map<? extends K, ? extends V> sourceMap = (Map<? extends K, ?
extends V>) DEFAULT_SOURCE_MAP;
+
+ /**
+ * Builds a new {@link ConcurrentReferenceHashMap}.
+ * <p>
+ * By default, keys are weak, and values are strong.
+ * </p>
+ * <p>
+ * The default values are:
+ * </p>
+ * <ul>
+ * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+ * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+ * <li>key reference type: {@link ReferenceType#WEAK}</li>
+ * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+ * <li>options: {@code null}</li>
+ * <li>source map: {@code null}</li>
+ * <li>value reference type: {@link ReferenceType#STRONG}</li>
+ * </ul>
+ */
+ @Override
+ public ConcurrentReferenceHashMap<K, V> get() {
+ final ConcurrentReferenceHashMap<K, V> 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<K, V> 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<K, V> 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<K, V> 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<K, V> setLoadFactor(final float loadFactor) {
+ this.loadFactor = loadFactor;
+ return this;
+ }
+
+ /**
+ * Sets the behavioral options.
+ *
+ * @param options the behavioral options.
+ * @return this instance.
+ */
+ public Builder<K, V> setOptions(final EnumSet<Option> 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<K, V> setSourceMap(final Map<? extends K, ? extends V>
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<K, V> setValueReferenceType(final ReferenceType
valueReferenceType) {
+ this.valueReferenceType = valueReferenceType;
+ return this;
+ }
+
+ /**
+ * Sets key reference type to {@link ReferenceType#SOFT}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> softKeys() {
+ setKeyReferenceType(ReferenceType.SOFT);
+ return this;
+ }
+
+ /**
+ * Sets value reference type to {@link ReferenceType#SOFT}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> softValues() {
+ setValueReferenceType(ReferenceType.SOFT);
+ return this;
+ }
+
+ /**
+ * Sets key reference type to {@link ReferenceType#STRONG}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> strongKeys() {
+ setKeyReferenceType(ReferenceType.STRONG);
+ return this;
+ }
+
+ /**
+ * Sets value reference type to {@link ReferenceType#STRONG}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> strongValues() {
+ setValueReferenceType(ReferenceType.STRONG);
+ return this;
+ }
+
+ /**
+ * Sets key reference type to {@link ReferenceType#WEAK}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> weakKeys() {
+ setKeyReferenceType(ReferenceType.WEAK);
+ return this;
+ }
+
+ /**
+ * Sets value reference type to {@link ReferenceType#WEAK}.
+ *
+ * @return this instance.
+ */
+ public Builder<K, V> 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<Entry<K, V>> {
+ private final InitializableEntry<K, V> entry = new
InitializableEntry<>();
+
+ @Override
+ public Entry<K, V> next() {
+ final HashEntry<K, V> e = super.nextEntry();
+ return entry.init(e.key(), e.value());
+ }
+ }
+
+ private final class EntryIterator extends HashIterator implements
Iterator<Entry<K, V>> {
+ @Override
+ public Entry<K, V> next() {
+ final HashEntry<K, V> e = super.nextEntry();
+ return new WriteThroughEntry(e.key(), e.value());
+ }
+ }
+
+ private final class EntrySet extends AbstractSet<Entry<K, V>> {
+
+ 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 Entry<?, ?> e = (Entry<?, ?>) o;
+ final V v = ConcurrentReferenceHashMap.this.get(e.getKey());
+ return v != null && v.equals(e.getValue());
+ }
+
+ @Override
+ public boolean isEmpty() {
+ return ConcurrentReferenceHashMap.this.isEmpty();
+ }
+
+ @Override
+ public Iterator<Entry<K, V>> 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.
+ * <p>
+ * 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.
+ * </p>
+ */
+ private static final class HashEntry<K, V> {
+
+ @SuppressWarnings("unchecked")
+ static <K, V> HashEntry<K, V>[] newArray(final int i) {
+ return new HashEntry[i];
+ }
+
+ private final Object keyRef;
+ private final int hash;
+ private volatile Object valueRef;
+ private final HashEntry<K, V> next;
+
+ HashEntry(final K key, final int hash, final HashEntry<K, V> next,
final V value, final ReferenceType keyType, final ReferenceType valueType,
+ final ReferenceQueue<Object> 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<V>) value).get();
+ }
+ return (V) value;
+ }
+
+ @SuppressWarnings("unchecked")
+ K key() {
+ if (keyRef instanceof KeyReference) {
+ return ((Reference<K>) keyRef).get();
+ }
+ return (K) keyRef;
+ }
+
+ Object newKeyReference(final K key, final ReferenceType keyType, final
ReferenceQueue<Object> 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<Object> 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<Object> refQueue) {
+ this.valueRef = newValueReference(value, valueType, refQueue);
+ }
+
+ V value() {
+ return dereferenceValue(valueRef);
+ }
+ }
+
+ private abstract class HashIterator {
+ private int nextSegmentIndex;
+ private int nextTableIndex;
+ private HashEntry<K, V>[] currentTable;
+ private HashEntry<K, V> nextEntry;
+ private HashEntry<K, V> 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<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 hasMoreElements() {
+ return hasNext();
+ }
+
+ 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 /* 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<K, V> implements Entry<K, V>
{
+ private K key;
+ private V value;
+
+ @Override
+ public K getKey() {
+ return key;
+ }
+
+ @Override
+ public V getValue() {
+ return value;
+ }
+
+ public Entry<K, V> 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<K>, Enumeration<K> {
+ @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<K> {
+ @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<K> 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.
+ * <p>
+ * 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.)
+ * </p>
+ * <p>
+ * 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:
+ * </p>
+ * <ul>
+ * <li>All (unsynchronized) read operations must first read the "count"
field, and should not look at table entries if it is 0.</li>
+ * <li>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.</li>
+ * </ul>
+ * <p>
+ * As a guide, all critical volatile reads and writes to the count field
are marked in code comments.
+ * </p>
+ */
+ private static final class Segment<K, V> extends ReentrantLock {
+
+ private static final long serialVersionUID = 1L;
+
+ @SuppressWarnings("unchecked")
+ static <K, V> Segment<K, V>[] 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 <tt>(int)(capacity *
+ * loadFactor)</tt>.)
+ */
+ private transient int threshold;
+
+ /**
+ * The per-segment table.
+ */
+ private transient volatile HashEntry<K, V>[] 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<Object> 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.<K, V>newArray(initialCapacity));
+ }
+
+ V apply(final K key, final int hash, final BiFunction<? super K, ?
super V, ? extends V> 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<? super
K, ? super V, ? extends V> 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<K, V>[] 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<K, V> 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<K, V>[] tab = table;
+ final int len = tab.length;
+ for (int i = 0; i < len; i++) {
+ for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
+ final Object opaque = e.valueRef;
+ V v;
+ if (opaque == null) {
+ // recheck
+ v = readValueUnderLock(e);
+ } else {
+ v = e.dereferenceValue(opaque);
+ }
+ if (value.equals(v)) {
+ return true;
+ }
+ }
+ }
+ }
+ return false;
+ }
+
+ /* Specialized implementations of map methods */
+ V get(final Object key, final int hash) {
+ // read-volatile
+ if (count != 0) {
+ HashEntry<K, V> 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<K, V> getFirst(final int hash) {
+ final HashEntry<K, V>[] tab = table;
+ return tab[hash & tab.length - 1];
+ }
+
+ V getValue(final K key, final V value, final Function<? super K, ?
extends V> function) {
+ return value != null ? value : function.apply(key);
+ }
+
+ private boolean keyEq(final Object src, final Object dest) {
+ return identityComparisons ? src == dest : src.equals(dest);
+ }
+
+ HashEntry<K, V> newHashEntry(final K key, final int hash, final
HashEntry<K, V> next, final V value) {
+ return new HashEntry<>(key, hash, next, value, keyType, valueType,
refQueue);
+ }
+
+ /**
+ * This method must be called with exactly one of <code>value</code>
and <code>function</code> non-null.
+ **/
+ V put(final K key, final int hash, final V value, final Function<?
super K, ? extends V> 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<? super K, ? extends V> 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<K, V>[] tab = table;
+ final int index = hash & tab.length - 1;
+ final HashEntry<K, V> first = tab[index];
+ HashEntry<K, V> e = first;
+ while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
+ e = e.next;
+ }
+ 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<K, V> e) {
+ lock();
+ try {
+ removeStale();
+ return e.value();
+ } finally {
+ unlock();
+ }
+ }
+
+ int rehash() {
+ final HashEntry<K, V>[] 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<K, V>[] 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<K, V> e = oldTable[i];
+ if (e != null) {
+ final HashEntry<K, V> 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<K, V> lastRun = e;
+ int lastIdx = idx;
+ for (HashEntry<K, V> 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<K, V> 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<K, V> 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<K, V>[] tab = table;
+ final int index = hash & tab.length - 1;
+ final HashEntry<K, V> first = tab[index];
+ HashEntry<K, V> 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<K, V> newFirst = e.next;
+ for (HashEntry<K, V> 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<K, V> 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<K, V> e = getFirst(hash);
+ while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
+ e = e.next;
+ }
+ boolean replaced = false;
+ if (e != null && oldValue.equals(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<K, V>[] newTable) {
+ threshold = (int) (newTable.length * loadFactor);
+ table = newTable;
+ refQueue = new ReferenceQueue<>();
+ }
+ }
+
+ private static class SimpleEntry<K, V> implements Entry<K, V> {
+
+ private static boolean eq(final Object o1, final Object o2) {
+ return o1 == null ? o2 == null : o1.equals(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<K> extends SoftReference<K>
implements KeyReference {
+
+ private final int hash;
+
+ SoftKeyReference(final K key, final int hash, final
ReferenceQueue<Object> refQueue) {
+ super(key, refQueue);
+ this.hash = hash;
+ }
+
+ @Override
+ public int keyHash() {
+ return hash;
+ }
+
+ @Override
+ public Object keyRef() {
+ return this;
+ }
+ }
+
+ private static final class SoftValueReference<V> extends SoftReference<V>
implements KeyReference {
+ private final Object keyRef;
+ private final int hash;
+
+ SoftValueReference(final V value, final Object keyRef, final int hash,
final ReferenceQueue<Object> 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<V>, Enumeration<V> {
+ @Override
+ public V next() {
+ return super.nextEntry().value();
+ }
+
+ @Override
+ public V nextElement() {
+ return super.nextEntry().value();
+ }
+ }
+
+ private final class Values extends AbstractCollection<V> {
+ @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<V> 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<K> extends WeakReference<K>
implements KeyReference {
+ private final int hash;
+
+ WeakKeyReference(final K key, final int hash, final
ReferenceQueue<Object> refQueue) {
+ super(key, refQueue);
+ this.hash = hash;
+ }
+
+ @Override
+ public int keyHash() {
+ return hash;
+ }
+
+ @Override
+ public Object keyRef() {
+ return this;
+ }
+ }
+
+ private static final class WeakValueReference<V> extends WeakReference<V>
implements KeyReference {
+ private final Object keyRef;
+ private final int hash;
+
+ WeakValueReference(final V value, final Object keyRef, final int hash,
final ReferenceQueue<Object> 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<K, V> {
+
+ 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) {
+ if (value == null) {
+ throw new NullPointerException();
+ }
+ 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<Option> 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.
+ * <p>
+ * By default, keys are weak, and values are strong.
+ * </p>
+ * <p>
+ * The default values are:
+ * </p>
+ * <ul>
+ * <li>concurrency level: {@value #DEFAULT_CONCURRENCY_LEVEL}</li>
+ * <li>initial capacity: {@value #DEFAULT_INITIAL_CAPACITY}</li>
+ * <li>key reference type: {@link ReferenceType#WEAK}</li>
+ * <li>load factor: {@value #DEFAULT_LOAD_FACTOR}</li>
+ * <li>options: {@code null}</li>
+ * <li>source map: {@code null}</li>
+ * <li>value reference type: {@link ReferenceType#STRONG}</li>
+ * </ul>
+ *
+ * @param <K> the type of keys.
+ * @param <V> the type of values.
+ * @return a new Builder.
+ */
+ public static <K, V> Builder<K, V> 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<K, V>[] segments;
+
+ private final boolean identityComparisons;
+
+ private transient Set<K> keySet;
+
+ private transient Set<Entry<K, V>> entrySet;
+
+ private transient Collection<V> values;
+
+ /**
+ * Creates a new, empty map with the specified initial capacity, reference
types, load factor, and concurrency level.
+ * <p>
+ * Behavioral changing options such as {@link Option#IDENTITY_COMPARISONS}
can also be specified.
+ * </p>
+ *
+ * @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<Option> 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<K, V> segment : segments) {
+ segment.clear();
+ }
+ }
+
+ @Override
+ public V compute(final K key, final BiFunction<? super K, ? super V, ?
extends V> remappingFunction) {
+ Objects.requireNonNull(key);
+ Objects.requireNonNull(remappingFunction);
+
+ final int hash = hashOf(key);
+ final Segment<K, V> 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:
+ *
+ * <pre>{@code
+ * if (map.get(key) == null) {
+ * V newValue = mappingFunction.apply(key);
+ * if (newValue != null)
+ * return map.putIfAbsent(key, newValue);
+ * }
+ * }</pre>
+ * <p>
+ * The default implementation may retry these steps when multiple threads
attempt updates including potentially calling the mapping function multiple
times.
+ * </p>
+ * <p>
+ * 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 <strong>must</strong>
override this default implementation.
+ * </p>
+ */
+ @Override
+ public V computeIfAbsent(final K key, final Function<? super K, ? extends
V> mappingFunction) {
+ Objects.requireNonNull(key);
+ Objects.requireNonNull(mappingFunction);
+
+ final int hash = hashOf(key);
+ final Segment<K, V> 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<? super K, ? super
V, ? extends V> remappingFunction) {
+ Objects.requireNonNull(key);
+ Objects.requireNonNull(remappingFunction);
+
+ final int hash = hashOf(key);
+ final Segment<K, V> 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) {
+ if (value == null) {
+ throw new NullPointerException();
+ }
+ // See explanation of modCount use above
+ final Segment<K, V>[] 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<K, V> segment : segments) {
+ segment.lock();
+ }
+ boolean found = false;
+ try {
+ for (final Segment<K, V> segment : segments) {
+ if (segment.containsValue(value)) {
+ found = true;
+ break;
+ }
+ }
+ } finally {
+ for (final Segment<K, V> 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.
+ * <p>
+ * 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.
+ * </p>
+ */
+ @Override
+ public Set<Entry<K, V>> entrySet() {
+ final Set<Entry<K, V>> es = entrySet;
+ return es != null ? es : (entrySet = new EntrySet(false));
+ }
+
+ /**
+ * Returns the value to which the specified key is mapped, or {@code null}
if this map contains no mapping for the key.
+ * <p>
+ * 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.)
+ * </p>
+ *
+ * @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<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.
+ //
+ 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.
+ * <p>
+ * 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.
+ * </p>
+ */
+ @Override
+ public Set<K> keySet() {
+ final Set<K> 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.
+ * <p>
+ * Note: this method will acquire locks one at a time across all segments
of this table, so this method should be used sparingly.
+ * </p>
+ */
+ public void purgeStaleEntries() {
+ for (final Segment<K, V> segment : segments) {
+ segment.removeStale();
+ }
+ }
+
+ /**
+ * 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 {@code get} method with a key
that is equal to the original key.
+ * </p>
+ *
+ * @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) {
+ if (key == null || value == null) {
+ throw new NullPointerException();
+ }
+ 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<? extends K, ? extends V> m) {
+ for (final Entry<? extends K, ? extends V> 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) {
+ if (value == null) {
+ throw new NullPointerException();
+ }
+ 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) {
+ if (value == null) {
+ throw new NullPointerException();
+ }
+ 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) {
+ if (oldValue == null || newValue == null) {
+ throw new NullPointerException();
+ }
+ 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<K, V> 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<K, V>[] 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<K, V> segment : segments) {
+ segment.lock();
+ }
+ for (final Segment<K, V> segment : segments) {
+ sum += segment.count;
+ }
+ for (final Segment<K, V> 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.
+ * <p>
+ * 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.
+ * </p>
+ */
+ @Override
+ public Collection<V> values() {
+ final Collection<V> vs = values;
+ return vs != null ? vs : (values = new Values());
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java
b/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java
new file mode 100644
index 000000000..97b57eb65
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/AbstractConcurrentReferenceHashMapTest.java
@@ -0,0 +1,58 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.EnumSet;
+
+import org.apache.commons.collections4.map.ConcurrentReferenceHashMap.Option;
+
+/**
+ * Tests {@link ConcurrentReferenceHashMap}.
+ *
+ * @param <K> the key type.
+ * @param <V> the value type.
+ */
+public abstract class AbstractConcurrentReferenceHashMapTest<K, V> extends
AbstractMapTest<K, V> {
+
+ protected static final EnumSet<Option> IDENTITY_COMPARISONS =
EnumSet.of(Option.IDENTITY_COMPARISONS);
+
+ public AbstractConcurrentReferenceHashMapTest() {
+ super(AbstractConcurrentReferenceHashMapTest.class.getSimpleName());
+ }
+
+ @Override
+ public boolean isAllowNullKey() {
+ return false;
+ }
+
+ @Override
+ public boolean isAllowNullValueGet() {
+ return false;
+ }
+
+ @Override
+ public boolean isAllowNullValuePut() {
+ return false;
+ }
+
+ @Override
+ public boolean isTestSerialization() {
+ return false;
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java
new file mode 100644
index 000000000..f50dba71d
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentHashMapSanityTest.java
@@ -0,0 +1,63 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * A sanity test for the test framework.
+ *
+ * @param <K> the key type.
+ * @param <V> the value type.
+ */
+public class ConcurrentHashMapSanityTest<K, V> extends AbstractMapTest<K, V> {
+
+ public ConcurrentHashMapSanityTest() {
+ super(ConcurrentHashMapSanityTest.class.getSimpleName());
+ }
+
+ @Override
+ public boolean isAllowNullKey() {
+ return false;
+ }
+
+ @Override
+ public boolean isAllowNullValueGet() {
+ return false;
+ }
+
+ @Override
+ public boolean isAllowNullValuePut() {
+ return false;
+ }
+
+ /**
+ * Don't test, just a sanity check for the test framework.
+ */
+ @Override
+ public boolean isTestSerialization() {
+ return false;
+ }
+
+ @Override
+ public Map<K, V> makeObject() {
+ return new ConcurrentHashMap<>();
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java
new file mode 100644
index 000000000..a1620b118
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapDefaultsTest.java
@@ -0,0 +1,31 @@
+/*
+ * 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.
+ */
+
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapDefaultsTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // The default behavior
+ return ConcurrentReferenceHashMap.<K, V>builder().get();
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java
new file mode 100644
index 000000000..5115dc3c2
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVSoftIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .softValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java
new file mode 100644
index 000000000..e22ca32a6
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVSoftTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVSoftTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .softValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java
new file mode 100644
index 000000000..6725a712b
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVStrongIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .strongValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java
new file mode 100644
index 000000000..e42b78975
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVStrongTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVStrongTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .strongValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java
new file mode 100644
index 000000000..90a29d02d
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVWeakIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .weakValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java
new file mode 100644
index 000000000..b53b2409e
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKSoftVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKSoftVWeakTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .softKeys()
+ .weakValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java
new file mode 100644
index 000000000..c824e6cea
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVSoftIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .softValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java
new file mode 100644
index 000000000..2d6291273
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVSoftTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVSoftTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .softValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java
new file mode 100644
index 000000000..40c1fc019
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVStrongIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .strongValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java
new file mode 100644
index 000000000..49148901d
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVStrongTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVStrongTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .strongValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java
new file mode 100644
index 000000000..9cb77a40f
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVWeakIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .weakValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java
new file mode 100644
index 000000000..b6c9abb92
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKStrongVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKStrongVWeakTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .strongKeys()
+ .weakValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java
new file mode 100644
index 000000000..8d3cb9b62
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVSoftIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .softValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java
new file mode 100644
index 000000000..20ed8b865
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVSoftTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVSoftTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .softValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java
new file mode 100644
index 000000000..3920af28a
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVStrongIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .strongValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java
new file mode 100644
index 000000000..f8ae54b2b
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVStrongTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVStrongTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .strongValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java
new file mode 100644
index 000000000..7c7db04fe
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakIdCTest.java
@@ -0,0 +1,35 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVWeakIdCTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .weakValues()
+ .setOptions(IDENTITY_COMPARISONS)
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java
new file mode 100644
index 000000000..867ea2b69
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapKWeakVWeakTest.java
@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import java.util.Map;
+
+public class ConcurrentReferenceHashMapKWeakVWeakTest<K, V> extends
AbstractConcurrentReferenceHashMapTest<K, V> {
+
+ @Override
+ public Map<K, V> makeObject() {
+ // @formatter:off
+ return ConcurrentReferenceHashMap.<K, V>builder()
+ .weakKeys()
+ .weakValues()
+ .get();
+ // @formatter:on
+ }
+
+}
diff --git
a/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java
new file mode 100644
index 000000000..08f47162e
--- /dev/null
+++
b/src/test/java/org/apache/commons/collections4/map/ConcurrentReferenceHashMapTest.java
@@ -0,0 +1,55 @@
+/*
+ * 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.
+ */
+
+package org.apache.commons.collections4.map;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.commons.collections4.map.ConcurrentReferenceHashMap.Option;
+import
org.apache.commons.collections4.map.ConcurrentReferenceHashMap.ReferenceType;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link ConcurrentReferenceHashMap}.
+ */
+public class ConcurrentReferenceHashMapTest {
+
+ @Test
+ public void testBuilderAll() {
+ final Map<Integer, String> map0 = new HashMap<>();
+ map0.put(1, "1");
+ // @formatter:off
+ final Map<Integer, String> map = ConcurrentReferenceHashMap.<Integer,
String>builder()
+ .setConcurrencyLevel(4)
+ .setInitialCapacity(32)
+ .setKeyReferenceType(ReferenceType.SOFT)
+ .setLoadFactor(0.74f)
+ .setOptions(EnumSet.of(Option.IDENTITY_COMPARISONS))
+ .setSourceMap(map0)
+ .get();
+ // @formatter:on
+ map0.put(2, "2");
+ assertTrue(map.containsKey(1));
+ assertFalse(map.containsKey(2));
+
+ }
+}
