/*
* Licensed 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.
*
* Contributions from 2013-2017 where performed either by US government
* employees, or under US Veterans Health Administration contracts.
*
* US Veterans Health Administration contributions by government employees
* are work of the U.S. Government and are not subject to copyright
* protection in the United States. Portions contributed by government
* employees are USGovWork (17USC §105). Not subject to copyright.
*
* Contribution by contractors to the US Veterans Health Administration
* during this period are contractually contributed under the
* Apache License, Version 2.0.
*
* See: https://www.usa.gov/government-works
*
* Contributions prior to 2013:
*
* Copyright (C) International Health Terminology Standards Development Organisation.
* Licensed under the Apache License, Version 2.0.
*
*/
/*
* 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
*/
package sh.isaac.api.collections.jsr166y;
//~--- JDK imports ------------------------------------------------------------
import java.io.IOException;
import java.io.Serializable;
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.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.Set;
import java.util.concurrent.locks.ReentrantLock;
//~--- classes ----------------------------------------------------------------
/**
* An advanced hash table supporting configurable garbage collection semantics of keys and values, optional
* referential-equality, full concurrency of retrievals, and adjustable expected concurrency for updates.
*
* This table is designed around specific advanced use-cases. If there is any doubt whether this table is for
* you, you most likely should be using
* {@link java.util.concurrent.ConcurrentHashMap} instead.
*
* This table 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
* table are periodically removed once their corresponding keys are no longer referenced outside of this
* table. In other words, this table 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 table;
* however, the entry may occupy space until a future table operation decides to reclaim it. For this reason,
* summary functions such as {@code size} and {@code isEmpty} might return a value greater than the observed
* number of entries. In order to support a high level of concurrency, stale entries are only reclaimed during
* blocking (usually mutating) operations.
*
* Enabling soft keys allows entries in this table to remain until their space is absolutely needed by the
* garbage collector. This is unlike weak keys which can be reclaimed as soon as they are no longer referenced
* by a normal strong reference. The primary use case for soft keys is a cache, which ideally occupies memory
* that is not in use for as long as possible.
*
* By default, values are held using a normal strong reference. This provides the commonly desired guarantee
* that a value will always have at least the same life-span as it's key. For this reason, care should be
* taken to ensure that a value never refers, either directly or indirectly, to its key, thereby preventing
* reclamation. If this is unavoidable, then it is recommended to use the same reference type in use for the
* key. However, it should be noted that non-strong values may disappear before their corresponding key.
*
* While this table does allow the use of both strong keys and values, it is recommended to use {@link java.util.concurrent.ConcurrentHashMap}
* for such a configuration, since it is optimized for that case.
*
* Just like {@link java.util.concurrent.ConcurrentHashMap}, this class obeys the same functional
* specification as {@link java.util.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 table 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> Retrieval operations (including {@code get}) generally do not block, so 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 table 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> The allowed concurrency among update operations is guided by the optional {@code concurrencyLevel}
* constructor argument (default {@code 16}), which is used as a hint for internal sizing. The table 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 table. 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 table is a relatively slow
* operation, so, when possible, it is a good idea to provide estimates of expected table sizes in
* constructors.
*
* <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> 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> This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html"> Java
* Collections Framework</a>.
*
* @author Doug Lea
* @author Jason T. Greene
* @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 java.util.concurrent.ConcurrentMap<K, V>, Serializable {
/** The Constant serialVersionUID. */
private static final long serialVersionUID = 7249069246763182397L;
/** The Constant DEFAULT_KEY_TYPE. */
/*
* ---------------- Constants --------------
*/
static final ReferenceType DEFAULT_KEY_TYPE = ReferenceType.WEAK;
/** The Constant DEFAULT_VALUE_TYPE. */
static final ReferenceType DEFAULT_VALUE_TYPE = ReferenceType.STRONG;
/**
* 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.
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The maximum number of segments to allow; used to bound constructor arguments.
*/
static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
/**
* 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.
*/
static final int RETRIES_BEFORE_LOCK = 2;
//~--- fields --------------------------------------------------------------
/*
* ---------------- Fields --------------
*/
/**
* Mask value for indexing into segments. The upper bits of a key's hash code are used to choose the
* segment.
*/
final int segmentMask;
/**
* Shift value for indexing within segments.
*/
final int segmentShift;
/** The segments, each of which is a specialized hash table. */
final Segment<K, V>[] segments;
/** The identity comparisons. */
boolean identityComparisons;
/** The key set. */
transient Set<K> keySet;
/** The entry set. */
transient Set<Map.Entry<K, V>> entrySet;
/** The values. */
transient Collection<V> values;
//~--- constant enums ------------------------------------------------------
/**
* The Enum Option.
*/
public static enum Option {
/**
* Indicates that referential-equality (== instead of .equals()) should be used when locating keys.
* This offers similar behavior to {@link IdentityHashMap}
*/
IDENTITY_COMPARISONS
}
/*
* The basic strategy is to subdivide the table among Segments, each of which itself is a concurrently
* readable hash table.
*/
/**
* An option specifying which Java reference type should be used to refer to a key and/or value.
*/
public static 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
}
;
;
//~--- constructors --------------------------------------------------------
/**
* Creates a new, empty map with a default initial capacity (16), reference types (weak keys, strong
* values), default load factor (0.75) and concurrencyLevel (16).
*/
public ConcurrentReferenceHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the specified initial capacity, and with default reference types (weak
* keys, strong values), load factor (0.75) and concurrencyLevel (16).
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to accommodate
* this many elements.
* @throws IllegalArgumentException if the initial capacity of elements is negative.
*/
public ConcurrentReferenceHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new map with the same mappings as the given map. The map is created with a capacity of 1.5
* times the number of mappings in the given map or 16 (whichever is greater), and a default load factor
* (0.75) and concurrencyLevel (16).
*
* @param m the map
*/
public ConcurrentReferenceHashMap(Map<? extends K, ? extends V> m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY),
DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL);
putAll(m);
}
/**
* Creates a new, empty map with the specified initial capacity and load factor and with the default
* reference types (weak keys, strong values), and concurrencyLevel (16).
*
* @param initialCapacity The implementation performs internal sizing to accommodate this many elements.
* @param loadFactor the load factor threshold, used to control resizing. Resizing may be performed when
* the average number of elements per bin exceeds this threshold.
* @throws IllegalArgumentException if the initial capacity of elements is negative or the load factor is
* nonpositive
*
* @since 1.6
*/
public ConcurrentReferenceHashMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty reference map with the specified key and value reference types.
*
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @throws IllegalArgumentException if the initial capacity of elements is negative.
*/
public ConcurrentReferenceHashMap(ReferenceType keyType, ReferenceType valueType) {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL, keyType, valueType, null);
}
/**
* Creates a new, empty map with the specified initial capacity, load factor and concurrency level.
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to accommodate
* this many elements.
* @param loadFactor the load factor threshold, used to control resizing. Resizing may be performed when
* the average number of elements per bin exceeds this threshold.
* @param concurrencyLevel the estimated number of concurrently updating threads. The implementation
* performs internal sizing to try to accommodate this many threads.
* @throws IllegalArgumentException if the initial capacity is negative or the load factor or
* concurrencyLevel are nonpositive.
*/
public ConcurrentReferenceHashMap(int initialCapacity, float loadFactor, int concurrencyLevel) {
this(initialCapacity, loadFactor, concurrencyLevel, DEFAULT_KEY_TYPE, DEFAULT_VALUE_TYPE, null);
}
/**
* Creates a new, empty map with the specified initial capacity, reference types and with default load
* factor (0.75) and concurrencyLevel (16).
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to accommodate
* this many elements.
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @throws IllegalArgumentException if the initial capacity of elements is negative.
*/
public ConcurrentReferenceHashMap(int initialCapacity, ReferenceType keyType, ReferenceType valueType) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL, keyType, valueType, null);
}
/**
* Creates a new, empty reference map with the specified reference types and behavioral options.
*
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @param options the options
* @throws IllegalArgumentException if the initial capacity of elements is negative.
*/
public ConcurrentReferenceHashMap(ReferenceType keyType, ReferenceType valueType, EnumSet<Option> options) {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL, keyType, valueType, options);
}
/*
* ---------------- Public operations --------------
*/
/**
* Creates a new, empty map with the specified initial capacity, reference types, load factor and
* concurrency level.
*
* Behavioral changing options such as {@link Option#IDENTITY_COMPARISONS} can also be specified.
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to accommodate
* this many elements.
* @param loadFactor the load factor threshold, used to control resizing. Resizing may be performed when
* the average number of elements per bin exceeds this threshold.
* @param concurrencyLevel the estimated number of concurrently updating threads. The implementation
* performs internal sizing to try to accommodate this many threads.
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @param options the behavioral options
* @throws IllegalArgumentException if the initial capacity is negative or the load factor or
* concurrencyLevel are nonpositive.
*/
public ConcurrentReferenceHashMap(int initialCapacity,
float loadFactor,
int concurrencyLevel,
ReferenceType keyType,
ReferenceType valueType,
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;
}
this.segmentShift = 32 - sshift;
this.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;
}
this.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, this.identityComparisons);
}
}
//~--- methods -------------------------------------------------------------
/**
* Removes all of the mappings from this map.
*/
@Override
public void clear() {
for (int i = 0; i < this.segments.length; ++i) {
this.segments[i].clear();
}
}
/**
* Legacy method testing if some key maps into the specified value in this table. This method is identical
* in functionality to
* {@link #containsValue}, and exists solely to ensure full compatibility with class {@link java.util.Hashtable},
* which supported this method prior to introduction of the Java Collections framework.
*
* @param value a value to search for
* @return {@code true} if and only if some key maps to the {@code value} argument in this table as
* determined by the {@code equals} method; {@code false} otherwise
* @throws NullPointerException if the specified value is null
*/
public boolean contains(Object value) {
return containsValue(value);
}
/**
* 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(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, and so is much slower than 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(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) {
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
mcsum += mc[i] = segments[i].modCount;
if (segments[i].containsValue(value)) {
return true;
}
}
boolean cleanSweep = true;
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
if (mc[i] != segments[i].modCount) {
cleanSweep = false;
break;
}
}
}
if (cleanSweep) {
return false;
}
}
// Resort to locking all segments
for (int i = 0; i < segments.length; ++i) {
segments[i].lock();
}
boolean found = false;
try {
for (int i = 0; i < segments.length; ++i) {
if (segments[i].containsValue(value)) {
found = true;
break;
}
}
} finally {
for (int i = 0; i < segments.length; ++i) {
segments[i].unlock();
}
}
return found;
}
/**
* Returns an enumeration of the values in this table.
*
* @return an enumeration of the values in this table
* @see #values()
*/
public Enumeration<V> elements() {
return new ValueIterator();
}
/**
* 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 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.
*
* @return the set
*/
@Override
public Set<Map.Entry<K, V>> entrySet() {
final Set<Map.Entry<K, V>> es = this.entrySet;
return (es != null) ? es
: (this.entrySet = new EntrySet());
}
/**
* 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.
*
* @return the set
*/
@Override
public Set<K> keySet() {
final Set<K> ks = this.keySet;
return (ks != null) ? ks
: (this.keySet = new KeySet());
}
/**
* Returns an enumeration of the keys in this table.
*
* @return an enumeration of the keys in this table
* @see #keySet()
*/
public Enumeration<K> keys() {
return new KeyIterator();
}
/**
* Removes any stale entries whose keys have been finalized. Use of this method is normally not necessary
* since stale entries are automatically removed lazily, when blocking operations are required. However,
* there are some cases where this operation should be performed eagerly, such as cleaning up old
* references to a ClassLoader in a multi-classloader environment.
*
* Note: this method will acquire locks, one at a time, across all segments of this table, so if it is to
* be used, it should be used sparingly.
*/
public void purgeStaleEntries() {
for (int i = 0; i < this.segments.length; ++i) {
this.segments[i].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.
*
* @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(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
final int hash = hashOf(key);
return segmentFor(hash).put(key, hash, value, 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(Map<? extends K, ? extends V> m) {
for (final Map.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(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
final int hash = hashOf(key);
return segmentFor(hash).put(key, hash, value, 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(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(Object key, 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(K key, 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(K key, V oldValue, 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 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) {
check = -1; // force retry
break;
}
}
}
if (check == sum) {
break;
}
}
if (check != sum) { // Resort to locking all segments
sum = 0;
for (int i = 0; i < segments.length; ++i) {
segments[i].lock();
}
for (int i = 0; i < segments.length; ++i) {
sum += segments[i].count;
}
for (int i = 0; i < segments.length; ++i) {
segments[i].unlock();
}
}
if (sum > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int) sum;
}
}
/**
* Returns 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.
*
* @return the collection
*/
@Override
public Collection<V> values() {
final Collection<V> vs = this.values;
return (vs != null) ? vs
: (this.values = new Values());
}
/**
* Returns the segment that should be used for key with given hash.
*
* @param hash the hash code for the key
* @return the segment
*/
final Segment<K, V> segmentFor(int hash) {
return this.segments[(hash >>> this.segmentShift) & this.segmentMask];
}
/*
* ---------------- Small Utilities --------------
*/
/**
* 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.
*
* @param h the h
* @return the int
*/
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);
}
/**
* Hash of.
*
* @param key the key
* @return the int
*/
private int hashOf(Object key) {
return hash(this.identityComparisons ? System.identityHashCode(key)
: key.hashCode());
}
/**
* Reconstitute the {@code ConcurrentReferenceHashMap} instance from a stream (i.e., deserialize it).
*
* @param s the stream
* @throws IOException Signals that an I/O exception has occurred.
* @throws ClassNotFoundException the class not found exception
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException {
s.defaultReadObject();
// Initialize each segment to be minimally sized, and let grow.
for (int i = 0; i < this.segments.length; ++i) {
this.segments[i].setTable(new HashEntry[1]);
}
// Read the keys and values, and put the mappings in the table
for (;;) {
final K key = (K) s.readObject();
final V value = (V) s.readObject();
if (key == null) {
break;
}
put(key, value);
}
}
/*
* ---------------- Serialization Support --------------
*/
/**
* Save the state of the {@code ConcurrentReferenceHashMap} instance to a stream (i.e., serialize it).
*
* @param s the stream
* @throws IOException Signals that an I/O exception has occurred.
* @serialData the key (Object) and value (Object) for each key-value mapping, followed by a null pair.
* The key-value mappings are emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws IOException {
s.defaultWriteObject();
for (int k = 0; k < this.segments.length; ++k) {
final Segment<K, V> seg = this.segments[k];
seg.lock();
try {
final HashEntry<K, V>[] tab = seg.table;
for (int i = 0; i < tab.length; ++i) {
for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
final K key = e.key();
if (key == null) // Skip GC'd keys
{
continue;
}
s.writeObject(key);
s.writeObject(e.value());
}
}
} finally {
seg.unlock();
}
}
s.writeObject(null);
s.writeObject(null);
}
//~--- get methods ---------------------------------------------------------
/**
* 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;
} else {
mcsum += mc[i] = segments[i].modCount;
}
}
// If mcsum happens to be zero, then we know we got a snapshot
// before any modifications at all were made. This is
// probably common enough to bother tracking.
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
if ((segments[i].count != 0) || (mc[i] != segments[i].modCount)) {
return false;
}
}
}
return true;
}
/**
* Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping
* for the key.
*
* <p>More formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code key.equals(k)}, then this method returns {@code v};
* otherwise it returns
* {@code null}. (There can be at most one such mapping.)
*
* @param key the key
* @return the v
* @throws NullPointerException if the specified key is null
*/
@Override
public V get(Object key) {
final int hash = hashOf(key);
return segmentFor(hash).get(key, hash);
}
//~--- inner interfaces ----------------------------------------------------
/**
* The Interface KeyReference.
*/
/*
* ---------------- Inner Classes --------------
*/
static interface KeyReference {
/**
* Key hash.
*
* @return the int
*/
int keyHash();
/**
* Key ref.
*
* @return the object
*/
Object keyRef();
}
//~--- inner classes -------------------------------------------------------
/**
* The Class EntryIterator.
*/
final class EntryIterator
extends HashIterator
implements Iterator<Entry<K, V>> {
/**
* Next.
*
* @return the map. entry
*/
@Override
public Map.Entry<K, V> next() {
final HashEntry<K, V> e = super.nextEntry();
return new WriteThroughEntry(e.key(), e.value());
}
}
/**
* The Class EntrySet.
*/
final class EntrySet
extends AbstractSet<Map.Entry<K, V>> {
/**
* Clear.
*/
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
/**
* Contains.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean contains(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
final V v = ConcurrentReferenceHashMap.this.get(e.getKey());
return (v != null) && v.equals(e.getValue());
}
/**
* Iterator.
*
* @return the iterator
*/
@Override
public Iterator<Map.Entry<K, V>> iterator() {
return new EntryIterator();
}
/**
* Removes the.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean remove(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
return ConcurrentReferenceHashMap.this.remove(e.getKey(), e.getValue());
}
/**
* Size.
*
* @return the int
*/
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
//~--- get methods ------------------------------------------------------
/**
* Checks if empty.
*
* @return true, if empty
*/
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
}
/**
* ConcurrentReferenceHashMap list entry. Note that this is never exported out as a user-visible
* Map.Entry.
*
* Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an
* unsynchronized reader to see null instead of initial value when read via a data race. Although a
* reordering leading to this is not likely to ever actually occur, the Segment.readValueUnderLock method
* is used as a backup in case a null (pre-initialized) value is ever seen in an unsynchronized access
* method.
*
* @param <K> the key type
* @param <V> the value type
*/
static final class HashEntry<K, V> {
/** The key ref. */
final Object keyRef;
/** The hash. */
final int hash;
/** The value ref. */
volatile Object valueRef;
/** The next. */
final HashEntry<K, V> next;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new hash entry.
*
* @param key the key
* @param hash the hash
* @param next the next
* @param value the value
* @param keyType the key type
* @param valueType the value type
* @param refQueue the ref queue
*/
HashEntry(K key,
int hash,
HashEntry<K, V> next,
V value,
ReferenceType keyType,
ReferenceType valueType,
ReferenceQueue<Object> refQueue) {
this.hash = hash;
this.next = next;
this.keyRef = newKeyReference(key, keyType, refQueue);
this.valueRef = newValueReference(value, valueType, refQueue);
}
//~--- methods ----------------------------------------------------------
/**
* Dereference value.
*
* @param value the value
* @return the v
*/
@SuppressWarnings("unchecked")
final V dereferenceValue(Object value) {
if (value instanceof KeyReference) {
return ((Reference<V>) value).get();
}
return (V) value;
}
/**
* Key.
*
* @return the k
*/
@SuppressWarnings("unchecked")
final K key() {
if (this.keyRef instanceof KeyReference) {
return ((Reference<K>) this.keyRef).get();
}
return (K) this.keyRef;
}
/**
* New array.
*
* @param <K> the key type
* @param <V> the value type
* @param i the i
* @return the hash entry[]
*/
@SuppressWarnings("unchecked")
static final <K, V> HashEntry<K, V>[] newArray(int i) {
return new HashEntry[i];
}
/**
* New key reference.
*
* @param key the key
* @param keyType the key type
* @param refQueue the ref queue
* @return the object
*/
final Object newKeyReference(K key, ReferenceType keyType, ReferenceQueue<Object> refQueue) {
if (keyType == ReferenceType.WEAK) {
return new WeakKeyReference<>(key, this.hash, refQueue);
}
if (keyType == ReferenceType.SOFT) {
return new SoftKeyReference<>(key, this.hash, refQueue);
}
return key;
}
/**
* New value reference.
*
* @param value the value
* @param valueType the value type
* @param refQueue the ref queue
* @return the object
*/
final Object newValueReference(V value, ReferenceType valueType, ReferenceQueue<Object> refQueue) {
if (valueType == ReferenceType.WEAK) {
return new WeakValueReference<>(value, this.keyRef, this.hash, refQueue);
}
if (valueType == ReferenceType.SOFT) {
return new SoftValueReference<>(value, this.keyRef, this.hash, refQueue);
}
return value;
}
/**
* Value.
*
* @return the v
*/
final V value() {
return dereferenceValue(this.valueRef);
}
//~--- set methods ------------------------------------------------------
/**
* Set value.
*
* @param value the value
* @param valueType the value type
* @param refQueue the ref queue
*/
final void setValue(V value, ReferenceType valueType, ReferenceQueue<Object> refQueue) {
this.valueRef = newValueReference(value, valueType, refQueue);
}
}
/**
* The Class HashIterator.
*/
/*
* ---------------- Iterator Support --------------
*/
abstract class HashIterator {
/** The next segment index. */
int nextSegmentIndex;
/** The next table index. */
int nextTableIndex;
/** The current table. */
HashEntry<K, V>[] currentTable;
/** The next entry. */
HashEntry<K, V> nextEntry;
/** The last returned. */
HashEntry<K, V> lastReturned;
/** The current key. */
K currentKey; // Strong reference to weak key (prevents gc)
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new hash iterator.
*/
HashIterator() {
this.nextSegmentIndex = ConcurrentReferenceHashMap.this.segments.length - 1;
this.nextTableIndex = -1;
advance();
}
//~--- methods ----------------------------------------------------------
/**
* Removes the.
*/
public void remove() {
if (this.lastReturned == null) {
throw new IllegalStateException();
}
ConcurrentReferenceHashMap.this.remove(this.currentKey);
this.lastReturned = null;
}
/**
* Advance.
*/
final void advance() {
if ((this.nextEntry != null) && (this.nextEntry = this.nextEntry.next) != null) {
return;
}
while (this.nextTableIndex >= 0) {
if ((this.nextEntry = this.currentTable[this.nextTableIndex--]) != null) {
return;
}
}
while (this.nextSegmentIndex >= 0) {
final Segment<K, V> seg = ConcurrentReferenceHashMap.this.segments[this.nextSegmentIndex--];
if (seg.count != 0) {
this.currentTable = seg.table;
for (int j = this.currentTable.length - 1; j >= 0; --j) {
if ((this.nextEntry = this.currentTable[j]) != null) {
this.nextTableIndex = j - 1;
return;
}
}
}
}
}
/**
* Next entry.
*
* @return the hash entry
*/
HashEntry<K, V> nextEntry() {
do {
if (this.nextEntry == null) {
throw new NoSuchElementException();
}
this.lastReturned = this.nextEntry;
this.currentKey = this.lastReturned.key();
advance();
} while (this.currentKey == null); // Skip GC'd keys
return this.lastReturned;
}
//~--- get methods ------------------------------------------------------
/**
* Checks for more elements.
*
* @return true, if successful
*/
public boolean hasMoreElements() {
return hasNext();
}
/**
* Checks for next.
*
* @return true, if successful
*/
public boolean hasNext() {
while (this.nextEntry != null) {
if (this.nextEntry.key() != null) {
return true;
}
advance();
}
return false;
}
}
/**
* The Class KeyIterator.
*/
final class KeyIterator
extends HashIterator
implements Iterator<K>, Enumeration<K> {
/**
* Next.
*
* @return the k
*/
@Override
public K next() {
return super.nextEntry()
.key();
}
/**
* Next element.
*
* @return the k
*/
@Override
public K nextElement() {
return super.nextEntry()
.key();
}
}
/**
* The Class KeySet.
*/
final class KeySet
extends AbstractSet<K> {
/**
* Clear.
*/
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
/**
* Contains.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean contains(Object o) {
return ConcurrentReferenceHashMap.this.containsKey(o);
}
/**
* Iterator.
*
* @return the iterator
*/
@Override
public Iterator<K> iterator() {
return new KeyIterator();
}
/**
* Removes the.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean remove(Object o) {
return ConcurrentReferenceHashMap.this.remove(o) != null;
}
/**
* Size.
*
* @return the int
*/
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
//~--- get methods ------------------------------------------------------
/**
* Checks if empty.
*
* @return true, if empty
*/
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
}
/**
* Segments are specialized versions of hash tables. This subclasses from ReentrantLock opportunistically,
* just to simplify some locking and avoid separate construction.
*
* @param <K> the key type
* @param <V> the value type
*/
static final class Segment<K, V>
extends ReentrantLock
implements Serializable {
/** The Constant serialVersionUID. */
/*
* Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so can be read
* without locking. Next fields of nodes are immutable (final). All list additions are performed at
* the front of each bin. This makes it easy to check changes, and also fast to traverse. When nodes
* would otherwise be changed, new nodes are created to replace them. This works well for hash tables
* since the bin lists tend to be short. (The average length is less than two for the default load
* factor threshold.)
*
* Read operations can thus proceed without locking, but rely on selected uses of volatiles to ensure
* that completed write operations performed by other threads are noticed. For most purposes, the
* "count" field, tracking the number of elements, serves as that volatile variable ensuring
* visibility. This is convenient because this field needs to be read in many read operations anyway:
*
* - All (unsynchronized) read operations must first read the "count" field, and should not look at
* table entries if it is 0.
*
* - All (synchronized) write operations should write to the "count" field after structurally changing
* any bin. The operations must not take any action that could even momentarily cause a concurrent
* read operation to see inconsistent data. This is made easier by the nature of the read operations
* in Map. For example, no operation can reveal that the table has grown but the threshold has not yet
* been updated, so there are no atomicity requirements for this with respect to reads.
*
* As a guide, all critical volatile reads and writes to the count field are marked in code comments.
*/
private static final long serialVersionUID = 2249069246763182397L;
//~--- fields -----------------------------------------------------------
/**
* The number of elements in this segment's region.
*/
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) must
* retry.
*/
transient int modCount;
/**
* The table is rehashed when its size exceeds this threshold. (The value of this field is always
* {@code (int)(capacity * loadFactor)}.)
*/
transient int threshold;
/**
* The per-segment table.
*/
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.
*
* @serial
*/
final float loadFactor;
/**
* The collected weak-key reference queue for this segment. This should be (re)initialized whenever
* table is assigned,
*/
transient volatile ReferenceQueue<Object> refQueue;
/** The key type. */
final ReferenceType keyType;
/** The value type. */
final ReferenceType valueType;
/** The identity comparisons. */
final boolean identityComparisons;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new segment.
*
* @param initialCapacity the initial capacity
* @param lf the lf
* @param keyType the key type
* @param valueType the value type
* @param identityComparisons the identity comparisons
*/
Segment(int initialCapacity,
float lf,
ReferenceType keyType,
ReferenceType valueType,
boolean identityComparisons) {
this.loadFactor = lf;
this.keyType = keyType;
this.valueType = valueType;
this.identityComparisons = identityComparisons;
setTable(HashEntry.<K, V>newArray(initialCapacity));
}
//~--- methods ----------------------------------------------------------
/**
* Clear.
*/
void clear() {
if (this.count != 0) {
lock();
try {
final HashEntry<K, V>[] tab = this.table;
for (int i = 0; i < tab.length; i++) {
tab[i] = null;
}
++this.modCount;
// replace the reference queue to avoid unnecessary stale cleanups
this.refQueue = new ReferenceQueue<>();
this.count = 0; // write-volatile
} finally {
unlock();
}
}
}
/**
* Contains key.
*
* @param key the key
* @param hash the hash
* @return true, if successful
*/
boolean containsKey(Object key, int hash) {
if (this.count != 0) { // read-volatile
HashEntry<K, V> e = getFirst(hash);
while (e != null) {
if ((e.hash == hash) && keyEq(key, e.key())) {
return true;
}
e = e.next;
}
}
return false;
}
/**
* Contains value.
*
* @param value the value
* @return true, if successful
*/
boolean containsValue(Object value) {
if (this.count != 0) { // read-volatile
final HashEntry<K, V>[] tab = this.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) {
v = readValueUnderLock(e); // recheck
} else {
v = e.dereferenceValue(opaque);
}
if (value.equals(v)) {
return true;
}
}
}
}
return false;
}
/**
* New array.
*
* @param <K> the key type
* @param <V> the value type
* @param i the i
* @return the segment[]
*/
@SuppressWarnings("unchecked")
static final <K, V> Segment<K, V>[] newArray(int i) {
return new Segment[i];
}
/**
* New hash entry.
*
* @param key the key
* @param hash the hash
* @param next the next
* @param value the value
* @return the hash entry
*/
HashEntry<K, V> newHashEntry(K key, int hash, HashEntry<K, V> next, V value) {
return new HashEntry<>(key, hash, next, value, this.keyType, this.valueType, this.refQueue);
}
/**
* Put.
*
* @param key the key
* @param hash the hash
* @param value the value
* @param onlyIfAbsent the only if absent
* @return the v
*/
V put(K key, int hash, V value, boolean onlyIfAbsent) {
lock();
try {
removeStale();
int c = this.count;
if (c++ > this.threshold) { // ensure capacity
final int reduced = rehash();
if (reduced > 0) // adjust from possible weak cleanups
{
this.count = (c -= reduced) - 1; // write-volatile
}
}
final HashEntry<K, V>[] tab = this.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 oldValue;
if (e != null) {
oldValue = e.value();
if (!onlyIfAbsent) {
e.setValue(value, this.valueType, this.refQueue);
}
} else {
oldValue = null;
++this.modCount;
tab[index] = newHashEntry(key, hash, first, value);
this.count = c; // write-volatile
}
return oldValue;
} finally {
unlock();
}
}
/**
* 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.
*
* @param e the e
* @return the v
*/
V readValueUnderLock(HashEntry<K, V> e) {
lock();
try {
removeStale();
return e.value();
} finally {
unlock();
}
}
/**
* Rehash.
*
* @return the int
*/
int rehash() {
final HashEntry<K, V>[] oldTable = this.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 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);
this.threshold = (int) (newTable.length * this.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());
}
}
}
}
this.table = newTable;
return reduce;
}
/**
* Remove; match on key only if value null, else match both.
*
* @param key the key
* @param hash the hash
* @param value the value
* @param refRemove the ref remove
* @return the v
*/
V remove(Object key, int hash, Object value, boolean refRemove) {
lock();
try {
if (!refRemove) {
removeStale();
}
int c = this.count - 1;
final HashEntry<K, V>[] tab = this.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.
++this.modCount;
HashEntry<K, V> newFirst = e.next;
for (HashEntry<K, V> p = first; p != e; p = p.next) {
final K pKey = p.key();
if (pKey == null) { // Skip GC'd keys
c--;
continue;
}
newFirst = newHashEntry(pKey, p.hash, newFirst, p.value());
}
tab[index] = newFirst;
this.count = c; // write-volatile
}
}
return oldValue;
} finally {
unlock();
}
}
/**
* Removes the stale.
*/
final void removeStale() {
KeyReference ref;
while ((ref = (KeyReference) this.refQueue.poll()) != null) {
remove(ref.keyRef(), ref.keyHash(), null, true);
}
}
/**
* Replace.
*
* @param key the key
* @param hash the hash
* @param newValue the new value
* @return the v
*/
V replace(K key, int hash, V newValue) {
lock();
try {
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, this.valueType, this.refQueue);
}
return oldValue;
} finally {
unlock();
}
}
/**
* Replace.
*
* @param key the key
* @param hash the hash
* @param oldValue the old value
* @param newValue the new value
* @return true, if successful
*/
boolean replace(K key, int hash, V oldValue, V newValue) {
lock();
try {
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, this.valueType, this.refQueue);
}
return replaced;
} finally {
unlock();
}
}
/**
* Key eq.
*
* @param src the src
* @param dest the dest
* @return true, if successful
*/
private boolean keyEq(Object src, Object dest) {
return this.identityComparisons ? src == dest
: src.equals(dest);
}
//~--- get methods ------------------------------------------------------
/**
* Returns properly casted first entry of bin for given hash.
*
* @param hash the hash
* @return the first
*/
HashEntry<K, V> getFirst(int hash) {
final HashEntry<K, V>[] tab = this.table;
return tab[hash & (tab.length - 1)];
}
/**
* Gets the.
*
* @param key the key
* @param hash the hash
* @return the v
*/
/*
* Specialized implementations of map methods
*/
V get(Object key, int hash) {
if (this.count != 0) { // read-volatile
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);
}
return readValueUnderLock(e); // recheck
}
e = e.next;
}
}
return null;
}
//~--- set methods ------------------------------------------------------
/**
* Sets table to new HashEntry array. Call only while holding lock or in constructor.
*
* @param newTable the new per-segment table
*/
void setTable(HashEntry<K, V>[] newTable) {
this.threshold = (int) (newTable.length * this.loadFactor);
this.table = newTable;
this.refQueue = new ReferenceQueue<>();
}
}
/**
* The Class SimpleEntry.
*
* @param <K> the key type
* @param <V> the value type
*/
/*
* This class is needed for JDK5 compatibility.
*/
static class SimpleEntry<K, V>
implements Entry<K, V>, java.io.Serializable {
/** The Constant serialVersionUID. */
private static final long serialVersionUID = -8499721149061103585L;
//~--- fields -----------------------------------------------------------
/** The key. */
private final K key;
/** The value. */
private V value;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new simple entry.
*
* @param entry the entry
*/
public SimpleEntry(Entry<? extends K, ? extends V> entry) {
this.key = entry.getKey();
this.value = entry.getValue();
}
/**
* Instantiates a new simple entry.
*
* @param key the key
* @param value the value
*/
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
//~--- methods ----------------------------------------------------------
/**
* Equals.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean equals(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
final Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
return eq(this.key, e.getKey()) && eq(this.value, e.getValue());
}
/**
* Hash code.
*
* @return the int
*/
@Override
public int hashCode() {
return ((this.key == null) ? 0
: this.key.hashCode()) ^ ((this.value == null) ? 0
: this.value.hashCode());
}
/**
* To string.
*
* @return the string
*/
@Override
public String toString() {
return this.key + "=" + this.value;
}
/**
* Eq.
*
* @param o1 the o 1
* @param o2 the o 2
* @return true, if successful
*/
private static boolean eq(Object o1, Object o2) {
return (o1 == null) ? o2 == null
: o1.equals(o2);
}
//~--- get methods ------------------------------------------------------
/**
* Gets the key.
*
* @return the key
*/
@Override
public K getKey() {
return this.key;
}
/**
* Gets the value.
*
* @return the value
*/
@Override
public V getValue() {
return this.value;
}
//~--- set methods ------------------------------------------------------
/**
* Set value.
*
* @param value the value
* @return the v
*/
@Override
public V setValue(V value) {
final V oldValue = this.value;
this.value = value;
return oldValue;
}
}
/**
* A soft-key reference which stores the key hash needed for reclamation.
*
* @param <K> the key type
*/
static final class SoftKeyReference<K>
extends SoftReference<K>
implements KeyReference {
/** The hash. */
final int hash;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new soft key reference.
*
* @param key the key
* @param hash the hash
* @param refQueue the ref queue
*/
SoftKeyReference(K key, int hash, ReferenceQueue<Object> refQueue) {
super(key, refQueue);
this.hash = hash;
}
//~--- methods ----------------------------------------------------------
/**
* Key hash.
*
* @return the int
*/
@Override
public final int keyHash() {
return this.hash;
}
/**
* Key ref.
*
* @return the object
*/
@Override
public final Object keyRef() {
return this;
}
}
/**
* The Class SoftValueReference.
*
* @param <V> the value type
*/
static final class SoftValueReference<V>
extends SoftReference<V>
implements KeyReference {
/** The key ref. */
final Object keyRef;
/** The hash. */
final int hash;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new soft value reference.
*
* @param value the value
* @param keyRef the key ref
* @param hash the hash
* @param refQueue the ref queue
*/
SoftValueReference(V value, Object keyRef, int hash, ReferenceQueue<Object> refQueue) {
super(value, refQueue);
this.keyRef = keyRef;
this.hash = hash;
}
//~--- methods ----------------------------------------------------------
/**
* Key hash.
*
* @return the int
*/
@Override
public final int keyHash() {
return this.hash;
}
/**
* Key ref.
*
* @return the object
*/
@Override
public final Object keyRef() {
return this.keyRef;
}
}
/**
* The Class ValueIterator.
*/
final class ValueIterator
extends HashIterator
implements Iterator<V>, Enumeration<V> {
/**
* Next.
*
* @return the v
*/
@Override
public V next() {
return super.nextEntry()
.value();
}
/**
* Next element.
*
* @return the v
*/
@Override
public V nextElement() {
return super.nextEntry()
.value();
}
}
/**
* The Class Values.
*/
final class Values
extends AbstractCollection<V> {
/**
* Clear.
*/
@Override
public void clear() {
ConcurrentReferenceHashMap.this.clear();
}
/**
* Contains.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean contains(Object o) {
return ConcurrentReferenceHashMap.this.containsValue(o);
}
/**
* Iterator.
*
* @return the iterator
*/
@Override
public Iterator<V> iterator() {
return new ValueIterator();
}
/**
* Size.
*
* @return the int
*/
@Override
public int size() {
return ConcurrentReferenceHashMap.this.size();
}
//~--- get methods ------------------------------------------------------
/**
* Checks if empty.
*
* @return true, if empty
*/
@Override
public boolean isEmpty() {
return ConcurrentReferenceHashMap.this.isEmpty();
}
}
/**
* A weak-key reference which stores the key hash needed for reclamation.
*
* @param <K> the key type
*/
static final class WeakKeyReference<K>
extends WeakReference<K>
implements KeyReference {
/** The hash. */
final int hash;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new weak key reference.
*
* @param key the key
* @param hash the hash
* @param refQueue the ref queue
*/
WeakKeyReference(K key, int hash, ReferenceQueue<Object> refQueue) {
super(key, refQueue);
this.hash = hash;
}
//~--- methods ----------------------------------------------------------
/**
* Key hash.
*
* @return the int
*/
@Override
public final int keyHash() {
return this.hash;
}
/**
* Key ref.
*
* @return the object
*/
@Override
public final Object keyRef() {
return this;
}
}
/**
* The Class WeakValueReference.
*
* @param <V> the value type
*/
static final class WeakValueReference<V>
extends WeakReference<V>
implements KeyReference {
/** The key ref. */
final Object keyRef;
/** The hash. */
final int hash;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new weak value reference.
*
* @param value the value
* @param keyRef the key ref
* @param hash the hash
* @param refQueue the ref queue
*/
WeakValueReference(V value, Object keyRef, int hash, ReferenceQueue<Object> refQueue) {
super(value, refQueue);
this.keyRef = keyRef;
this.hash = hash;
}
//~--- methods ----------------------------------------------------------
/**
* Key hash.
*
* @return the int
*/
@Override
public final int keyHash() {
return this.hash;
}
/**
* Key ref.
*
* @return the object
*/
@Override
public final Object keyRef() {
return this.keyRef;
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying map.
*/
final class WriteThroughEntry
extends SimpleEntry<K, V> {
/** The Constant serialVersionUID. */
private static final long serialVersionUID = -7900634345345313646L;
//~--- constructors -----------------------------------------------------
/**
* Instantiates a new write through entry.
*
* @param k the k
* @param v the v
*/
WriteThroughEntry(K k, V v) {
super(k, v);
}
//~--- set methods ------------------------------------------------------
/**
* Set our entry's value and write through to the map. The value to return is somewhat arbitrary here.
* Since a WriteThroughEntry does not necessarily track asynchronous changes, the most recent
* "previous" value could be different from what we return (or could even have been removed in which
* case the put will re-establish). We do not and cannot guarantee more.
*
* @param value the value
* @return the v
*/
@Override
public V setValue(V value) {
if (value == null) {
throw new NullPointerException();
}
final V v = super.setValue(value);
ConcurrentReferenceHashMap.this.put(getKey(), value);
return v;
}
}
}