org.glassfish.pfl.basic.concurrent.WeakHashMapSafeReadLock Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2019 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.glassfish.pfl.basic.concurrent ;
import java.lang.ref.WeakReference;
import java.lang.ref.ReferenceQueue;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* A hashtable-based Map implementation with weak keys.
* An entry in a WeakHashMap will automatically be removed when
* its key is no longer in ordinary use. More precisely, the presence of a
* mapping for a given key will not prevent the key from being discarded by the
* garbage collector, that is, made finalizable, finalized, and then reclaimed.
* When a key has been discarded its entry is effectively removed from the map,
* so this class behaves somewhat differently from other Map
* implementations.
*
* Both null values and the null key are supported. This class has
* performance characteristics similar to those of the HashMap
* class, and has the same efficiency parameters of initial capacity
* and load factor.
*
*
Like most collection classes, this class is not synchronized.
* A synchronized WeakHashMap may be constructed using the
* Collections.synchronizedMap method.
*
*
This class is intended primarily for use with key objects whose
* equals methods test for object identity using the
* == operator. Once such a key is discarded it can never be
* recreated, so it is impossible to do a lookup of that key in a
* WeakHashMap at some later time and be surprised that its entry
* has been removed. This class will work perfectly well with key objects
* whose equals methods are not based upon object identity, such
* as String instances. With such recreatable key objects,
* however, the automatic removal of WeakHashMap entries whose
* keys have been discarded may prove to be confusing.
*
*
The behavior of the WeakHashMap class depends in part upon
* the actions of the garbage collector, so several familiar (though not
* required) Map invariants do not hold for this class. Because
* the garbage collector may discard keys at any time, a
* WeakHashMap may behave as though an unknown thread is silently
* removing entries. In particular, even if you synchronize on a
* WeakHashMap instance and invoke none of its mutator methods, it
* is possible for the size method to return smaller values over
* time, for the isEmpty method to return false and
* then true, for the containsKey method to return
* true and later false for a given key, for the
* get method to return a value for a given key but later return
* null, for the put method to return
* null and the remove method to return
* false for a key that previously appeared to be in the map, and
* for successive examinations of the key set, the value collection, and
* the entry set to yield successively smaller numbers of elements.
*
*
Each key object in a WeakHashMap is stored indirectly as
* the referent of a weak reference. Therefore a key will automatically be
* removed only after the weak references to it, both inside and outside of the
* map, have been cleared by the garbage collector.
*
*
Implementation note: The value objects in a
* WeakHashMap are held by ordinary strong references. Thus care
* should be taken to ensure that value objects do not strongly refer to their
* own keys, either directly or indirectly, since that will prevent the keys
* from being discarded. Note that a value object may refer indirectly to its
* key via the WeakHashMap itself; that is, a value object may
* strongly refer to some other key object whose associated value object, in
* turn, strongly refers to the key of the first value object. One way
* to deal with this is to wrap values themselves within
* WeakReferences before
* inserting, as in: m.put(key, new WeakReference(value)),
* and then unwrapping upon each get.
*
*
The iterators returned by the iterator method of the collections
* returned by all of this class's "collection view methods" are
* fail-fast: if the map is structurally modified at any time after the
* iterator is created, in any way except through the iterator's own
* remove method, the iterator will throw a {@link
* ConcurrentModificationException}. Thus, in the face of concurrent
* modification, the iterator fails quickly and cleanly, rather than risking
* arbitrary, non-deterministic behavior at an undetermined time in the future.
*
*
Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw ConcurrentModificationException on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: the fail-fast behavior of iterators
* should be used only to detect bugs.
*
*
This class is a member of the
*
* Java Collections Framework.
*
*
This is copied directly from JDK 6 to get a version with the fix
* for but 6425537.
*
* @param the type of keys maintained by this map
* @param the type of mapped values
*
* @version %I%, %G%
* @author Doug Lea
* @author Josh Bloch
* @author Mark Reinhold
* @since 1.2
* @see java.util.HashMap
* @see java.lang.ref.WeakReference
*/
public class WeakHashMapSafeReadLock
extends AbstractMap
implements Map {
/**
* The default initial capacity -- MUST be a power of two.
*/
private static final int DEFAULT_INITIAL_CAPACITY = 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.
*/
private static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The load fast used when none specified in constructor.
*/
private static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The table, resized as necessary. Length MUST Always be a power of two.
*/
private Entry[] table;
/**
* The number of key-value mappings contained in this weak hash map.
*/
private int size;
/**
* The next size value at which to resize (capacity * load factor).
*/
private int threshold;
/**
* The load factor for the hash table.
*/
private final float loadFactor;
/**
* Reference queue for cleared WeakEntries
*/
private final ReferenceQueue queue = new ReferenceQueue();
/**
* The number of times this WeakHashMap has been structurally modified.
* Structural modifications are those that change the number of
* mappings in the map or otherwise modify its internal structure
* (e.g., rehash). This field is used to make iterators on
* Collection-views of the map fail-fast.
*
* @see ConcurrentModificationException
*/
private volatile int modCount;
/**
* Constructs a new, empty WeakHashMap with the given initial
* capacity and the given load factor.
*
* @param initialCapacity The initial capacity of the WeakHashMap
* @param loadFactor The load factor of the WeakHashMap
* @throws IllegalArgumentException if the initial capacity is negative,
* or if the load factor is nonpositive.
*/
public WeakHashMapSafeReadLock(int initialCapacity, float loadFactor) {
if (initialCapacity < 0) {
throw new IllegalArgumentException(
"Illegal Initial Capacity: " + initialCapacity);
}
if (initialCapacity > MAXIMUM_CAPACITY) {
initialCapacity = MAXIMUM_CAPACITY;
}
if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
throw new IllegalArgumentException("Illegal Load factor: " +
loadFactor);
}
int capacity = 1;
while (capacity < initialCapacity) {
capacity <<= 1;
}
table = new Entry[capacity];
this.loadFactor = loadFactor;
threshold = (int)(capacity * loadFactor);
}
/**
* Constructs a new, empty WeakHashMap with the given initial
* capacity and the default load factor (0.75).
*
* @param initialCapacity The initial capacity of the WeakHashMap
* @throws IllegalArgumentException if the initial capacity is negative
*/
public WeakHashMapSafeReadLock(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs a new, empty WeakHashMap with the default initial
* capacity (16) and load factor (0.75).
*/
public WeakHashMapSafeReadLock() {
this.loadFactor = DEFAULT_LOAD_FACTOR;
threshold = DEFAULT_INITIAL_CAPACITY;
table = new Entry[DEFAULT_INITIAL_CAPACITY];
}
/**
* Constructs a new WeakHashMap with the same mappings as the
* specified map. The WeakHashMap is created with the default
* load factor (0.75) and an initial capacity sufficient to hold the
* mappings in the specified map.
*
* @param m the map whose mappings are to be placed in this map
* @throws NullPointerException if the specified map is null
* @since 1.3
*/
public WeakHashMapSafeReadLock(Map m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 16),
DEFAULT_LOAD_FACTOR);
putAll(m);
}
// internal utilities
/**
* Value representing null keys inside tables.
*/
private static final Object NULL_KEY = new Object();
/**
* Use NULL_KEY for key if it is null.
*/
private static Object maskNull(Object key) {
return (key == null ? NULL_KEY : key);
}
/**
* Returns internal representation of null key back to caller as null.
*/
private static K unmaskNull(Object key) {
return (K) (key == NULL_KEY ? null : key);
}
/**
* Checks for equality of non-null reference x and possibly-null y. By
* default uses Object.equals.
*/
static boolean eq(Object x, Object y) {
return x == y || x.equals(y);
}
/**
* Returns index for hash code h.
*/
static int indexFor(int h, int length) {
return h & (length-1);
}
/**
* Expunges stale entries from the table.
*/
@SuppressWarnings("unchecked")
private void expungeStaleEntries() {
Entry e;
while ( (e = (Entry) queue.poll()) != null) {
// Fix for 6425537: WeakHashMap should be safe for concurrent get
synchronized( queue ) {
int h = e.hash;
int i = indexFor(h, table.length);
Entry prev = table[i];
Entry p = prev;
while (p != null) {
Entry next = p.next;
if (p == e) {
if (prev == e) {
table[i] = next;
} else {
prev.next = next;
}
e.next = null; // Help GC
e.value = null; // " "
size--;
break;
}
prev = p;
p = next;
}
}
}
}
/**
* Returns the table after first expunging stale entries.
*/
private Entry[] getTable() {
expungeStaleEntries();
return table;
}
/**
* Returns the number of key-value mappings in this map.
* This result is a snapshot, and may not reflect unprocessed
* entries that will be removed before next attempted access
* because they are no longer referenced.
*/
public int size() {
if (size == 0) {
return 0;
}
expungeStaleEntries();
return size;
}
/**
* Returns true if this map contains no key-value mappings.
* This result is a snapshot, and may not reflect unprocessed
* entries that will be removed before next attempted access
* because they are no longer referenced.
*/
@Override
public boolean isEmpty() {
return size() == 0;
}
static int computeHash( int h ) {
int hash = h ^ (h >>> 20) ^ (h >>> 12) ;
return hash ^ (hash >>> 7) ^ (hash >>> 4) ;
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* More formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code (key==null ? k==null :
* key.equals(k))}, then this method returns {@code v}; otherwise
* it returns {@code null}. (There can be at most one such mapping.)
*
*
A return value of {@code null} does not necessarily
* indicate that the map contains no mapping for the key; it's also
* possible that the map explicitly maps the key to {@code null}.
* The {@link #containsKey containsKey} operation may be used to
* distinguish these two cases.
*
* @see #put(Object, Object)
*/
@Override
public V get(Object key) {
Object k = maskNull(key);
int h = computeHash(k.hashCode());
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
@SuppressWarnings("unchecked")
Entry e = tab[index];
while (e != null) {
if (e.hash == h && eq(k, e.get())) {
return e.value;
}
e = e.next;
}
return null;
}
/**
* Returns true if this map contains a mapping for the
* specified key.
*
* @param key The key whose presence in this map is to be tested
* @return true if there is a mapping for key;
* false otherwise
*/
@Override
public boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Returns the entry associated with the specified key in this map.
* Returns null if the map contains no mapping for this key.
*/
Entry getEntry(Object key) {
Object k = maskNull(key);
int h = computeHash(k.hashCode());
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
@SuppressWarnings("unchecked")
Entry e = tab[index];
while (e != null && !(e.hash == h && eq(k, e.get()))) {
e = e.next;
}
return e;
}
/**
* Associates the specified value with the specified key in this map.
* If the map previously contained a mapping for this key, the old
* value is replaced.
*
* @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 key, or
* null if there was no mapping for key.
* (A null return can also indicate that the map
* previously associated null with key.)
*/
@Override
public V put(K key, V value) {
@SuppressWarnings("unchecked")
K k = (K) maskNull(key);
int h = computeHash(k.hashCode());
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
for (@SuppressWarnings("unchecked")
Entry e = tab[i]; e != null; e = e.next) {
if (h == e.hash && eq(k, e.get())) {
V oldValue = e.value;
if (value != oldValue) {
e.value = value;
}
return oldValue;
}
}
modCount++;
@SuppressWarnings("unchecked")
Entry e = tab[i];
tab[i] = new Entry(k, value, queue, h, e);
if (++size >= threshold) {
resize(tab.length * 2);
}
return null;
}
/**
* Rehashes the contents of this map into a new array with a
* larger capacity. This method is called automatically when the
* number of keys in this map reaches its threshold.
*
* If current capacity is MAXIMUM_CAPACITY, this method does not
* resize the map, but sets threshold to Integer.MAX_VALUE.
* This has the effect of preventing future calls.
*
* @param newCapacity the new capacity, MUST be a power of two;
* must be greater than current capacity unless current
* capacity is MAXIMUM_CAPACITY (in which case value
* is irrelevant).
*/
void resize(int newCapacity) {
Entry[] oldTable = getTable();
int oldCapacity = oldTable.length;
if (oldCapacity == MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return;
}
Entry[] newTable = new Entry[newCapacity];
transfer(oldTable, newTable);
table = newTable;
/*
* If ignoring null elements and processing ref queue caused massive
* shrinkage, then restore old table. This should be rare, but avoids
* unbounded expansion of garbage-filled tables.
*/
if (size >= threshold / 2) {
threshold = (int)(newCapacity * loadFactor);
} else {
expungeStaleEntries();
transfer(newTable, oldTable);
table = oldTable;
}
}
/** Transfers all entries from src to dest tables */
@SuppressWarnings("unchecked")
private void transfer(Entry[] src, Entry[] dest) {
for (int j = 0; j < src.length; ++j) {
@SuppressWarnings("unchecked")
Entry e = src[j];
src[j] = null;
while (e != null) {
Entry next = e.next;
Object key = e.get();
if (key == null) {
e.next = null; // Help GC
e.value = null; // " "
size--;
} else {
int i = indexFor(e.hash, dest.length);
e.next = dest[i];
dest[i] = e;
}
e = next;
}
}
}
/**
* Copies all of the mappings from the specified map to this map.
* These mappings will 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.
* @throws NullPointerException if the specified map is null.
*/
@Override
public void putAll(Map m) {
int numKeysToBeAdded = m.size();
if (numKeysToBeAdded == 0) {
return;
}
/*
* Expand the map if the map if the number of mappings to be added
* is greater than or equal to threshold. This is conservative; the
* obvious condition is (m.size() + size) >= threshold, but this
* condition could result in a map with twice the appropriate capacity,
* if the keys to be added overlap with the keys already in this map.
* By using the conservative calculation, we subject ourself
* to at most one extra resize.
*/
if (numKeysToBeAdded > threshold) {
int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
if (targetCapacity > MAXIMUM_CAPACITY) {
targetCapacity = MAXIMUM_CAPACITY;
}
int newCapacity = table.length;
while (newCapacity < targetCapacity) {
newCapacity <<= 1;
}
if (newCapacity > table.length) {
resize(newCapacity);
}
}
for (Map.Entry e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
/**
* Removes the mapping for a key from this weak hash map if it is present.
* More formally, if this map contains a mapping from key k to
* value v such that (key==null ? k==null :
* key.equals(k)), that mapping is removed. (The map can contain
* at most one such mapping.)
*
* Returns the value to which this map previously associated the key,
* or null if the map contained no mapping for the key. A
* return value of null does not necessarily indicate
* that the map contained no mapping for the key; it's also possible
* that the map explicitly mapped the key to null.
*
*
The map will not contain a mapping for the specified key once the
* call returns.
*
* @param key key whose mapping is to be removed from the map
* @return the previous value associated with key, or
* null if there was no mapping for key
*/
@Override
public V remove(Object key) {
Object k = maskNull(key);
int h = computeHash(k.hashCode());
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
@SuppressWarnings("unchecked")
Entry prev = tab[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (h == e.hash && eq(k, e.get())) {
modCount++;
size--;
if (prev == e) {
tab[i] = next;
} else {
prev.next = next;
}
return e.value;
}
prev = e;
e = next;
}
return null;
}
/** Special version of remove needed by Entry set */
Entry removeMapping(Object o) {
if (!(o instanceof Map.Entry)) {
return null;
}
Entry[] tab = getTable();
Map.Entry entry = (Map.Entry)o;
Object k = maskNull(entry.getKey());
int h = computeHash(k.hashCode());
int i = indexFor(h, tab.length);
@SuppressWarnings("unchecked")
Entry prev = tab[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (h == e.hash && e.equals(entry)) {
modCount++;
size--;
if (prev == e) {
tab[i] = next;
} else {
prev.next = next;
}
return e;
}
prev = e;
e = next;
}
return null;
}
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
public void clear() {
// clear out ref queue. We don't need to expunge entries
// since table is getting cleared.
while (queue.poll() != null)
;
modCount++;
Entry[] tab = table;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
size = 0;
// Allocation of array may have caused GC, which may have caused
// additional entries to go stale. Removing these entries from the
// reference queue will make them eligible for reclamation.
while (queue.poll() != null)
;
}
/**
* Returns true if this map maps one or more keys to the
* specified value.
*
* @param value value whose presence in this map is to be tested
* @return true if this map maps one or more keys to the
* specified value
*/
public boolean containsValue(Object value) {
if (value==null)
return containsNullValue();
Entry[] tab = getTable();
for (int i = tab.length ; i-- > 0 ;)
for (Entry e = tab[i] ; e != null ; e = e.next)
if (value.equals(e.value))
return true;
return false;
}
/**
* Special-case code for containsValue with null argument
*/
private boolean containsNullValue() {
Entry[] tab = getTable();
for (int i = tab.length ; i-- > 0 ;)
for (Entry e = tab[i] ; e != null ; e = e.next)
if (e.value==null)
return true;
return false;
}
/**
* The entries in this hash table extend WeakReference, using its main ref
* field as the key.
*/
private static class Entry extends WeakReference implements Map.Entry {
private V value;
private final int hash;
private Entry next;
/**
* Creates new entry.
*/
Entry(K key, V value,
ReferenceQueue queue,
int hash, Entry next) {
super(key, queue);
this.value = value;
this.hash = hash;
this.next = next;
}
public K getKey() {
return WeakHashMapSafeReadLock.unmaskNull(get());
}
public V getValue() {
return value;
}
public V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
Object k1 = getKey();
Object k2 = e.getKey();
if (k1 == k2 || (k1 != null && k1.equals(k2))) {
Object v1 = getValue();
Object v2 = e.getValue();
if (v1 == v2 || (v1 != null && v1.equals(v2)))
return true;
}
return false;
}
public int hashCode() {
Object k = getKey();
Object v = getValue();
return ((k==null ? 0 : k.hashCode()) ^
(v==null ? 0 : v.hashCode()));
}
public String toString() {
return getKey() + "=" + getValue();
}
}
private abstract class HashIterator implements Iterator {
int index;
Entry entry = null;
Entry lastReturned = null;
int expectedModCount = modCount;
/**
* Strong reference needed to avoid disappearance of key
* between hasNext and next
*/
Object nextKey = null;
/**
* Strong reference needed to avoid disappearance of key
* between nextEntry() and any use of the entry
*/
Object currentKey = null;
HashIterator() {
index = (size() != 0 ? table.length : 0);
}
public boolean hasNext() {
Entry[] t = table;
while (nextKey == null) {
Entry e = entry;
int i = index;
while (e == null && i > 0)
e = t[--i];
entry = e;
index = i;
if (e == null) {
currentKey = null;
return false;
}
nextKey = e.get(); // hold on to key in strong ref
if (nextKey == null)
entry = entry.next;
}
return true;
}
/** The common parts of next() across different types of iterators */
protected Entry nextEntry() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
if (nextKey == null && !hasNext())
throw new NoSuchElementException();
lastReturned = entry;
entry = entry.next;
currentKey = nextKey;
nextKey = null;
return lastReturned;
}
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
WeakHashMapSafeReadLock.this.remove(currentKey);
expectedModCount = modCount;
lastReturned = null;
currentKey = null;
}
}
private class ValueIterator extends HashIterator {
public V next() {
return nextEntry().value;
}
}
private class KeyIterator extends HashIterator {
public K next() {
return nextEntry().getKey();
}
}
private class EntryIterator extends HashIterator> {
public Map.Entry next() {
return nextEntry();
}
}
// Views
private transient Set> entrySet = null;
private transient volatile Set myKeySet = null ;
private transient volatile Collection myValues = null ;
/**
* 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. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own remove operation), the results of
* the iteration are undefined. The set supports element removal,
* which removes the corresponding mapping from the map, via the
* Iterator.remove, Set.remove,
* removeAll, retainAll, and clear
* operations. It does not support the add or addAll
* operations.
*/
public Set keySet() {
Set ks = myKeySet;
return (ks != null ? ks : (myKeySet = new KeySet()));
}
private class KeySet extends AbstractSet {
public Iterator iterator() {
return new KeyIterator();
}
public int size() {
return WeakHashMapSafeReadLock.this.size();
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
if (containsKey(o)) {
WeakHashMapSafeReadLock.this.remove(o);
return true;
}
else
return false;
}
public void clear() {
WeakHashMapSafeReadLock.this.clear();
}
}
/**
* 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. If the map is
* modified while an iteration over the collection is in progress
* (except through the iterator's own remove operation),
* the results of the iteration are undefined. The collection
* supports element removal, which removes the corresponding
* mapping from the map, via the Iterator.remove,
* Collection.remove, removeAll,
* retainAll and clear operations. It does not
* support the add or addAll operations.
*/
public Collection values() {
Collection vs = myValues;
return (vs != null ? vs : (myValues = new Values()));
}
private class Values extends AbstractCollection {
public Iterator iterator() {
return new ValueIterator();
}
public int size() {
return WeakHashMapSafeReadLock.this.size();
}
public boolean contains(Object o) {
return containsValue(o);
}
public void clear() {
WeakHashMapSafeReadLock.this.clear();
}
}
/**
* 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. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own remove operation, or through the
* setValue operation on a map entry returned by the
* iterator) the results of the iteration are undefined. The set
* supports element removal, which removes the corresponding
* mapping from the map, via the Iterator.remove,
* Set.remove, removeAll, retainAll and
* clear operations. It does not support the
* add or addAll operations.
*/
public Set> entrySet() {
Set> es = entrySet;
return es != null ? es : (entrySet = new EntrySet());
}
private class EntrySet extends AbstractSet> {
public Iterator> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry)o;
Entry candidate = getEntry(e.getKey());
return candidate != null && candidate.equals(e);
}
@Override
public boolean remove(Object o) {
return removeMapping(o) != null;
}
@Override
public int size() {
return WeakHashMapSafeReadLock.this.size();
}
@Override
public void clear() {
WeakHashMapSafeReadLock.this.clear();
}
private List> deepCopy() {
List> list = new ArrayList>(size());
for (Map.Entry e : this)
list.add(new AbstractMap.SimpleEntry(e));
return list;
}
public Object[] toArray() {
return deepCopy().toArray();
}
public T[] toArray(T[] a) {
return deepCopy().toArray(a);
}
}
}