Mega Code Archive
A hashtable-based Map implementation with weak keys and using reference-equality in place of object-equality wh
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/*
* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* A hashtable-based <tt>Map</tt> implementation with <em>weak keys</em> and
* using reference-equality in place of object-equality when comparing keys (and
* values). In an <tt>WeakIdentityHashMap</tt>, two keys <tt>k1</tt> and
* <tt>k2</tt> are considered equal if and only if <tt>(k1==k2)</tt>. An
* entry in a <tt>WeakIdentityHashMap</tt> 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.
*
* <p>
* Based on java.util.WeakHashMap
* </p>
*
* @author Dawid Kurzyniec
* @version <tt>$Revision: 2787 $</tt>
* @author <a href="mailto:kabir.khan@jboss.org">Kabir Khan</a>
* @see java.util.IdentityHashMap
* @see java.util.WeakHashMap
*/
@SuppressWarnings("unchecked")
public class WeakIdentityHashMap /* 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 HashMap has been structurally modified Structural
* modifications are those that change the number of mappings in the HashMap
* or otherwise modify its internal structure (e.g., rehash). This field is
* used to make iterators on Collection-views of the HashMap fail-fast. (See
* ConcurrentModificationException).
*/
private volatile int modCount;
/**
* Each of these fields are initialized to contain an instance of the
* appropriate view the first time this view is requested. The views are
* stateless, so there's no reason to create more than one of each.
*/
transient volatile Set keySet = null;
transient volatile Collection values = null;
/**
* Constructs a new, empty <tt>WeakIdentityHashMap</tt> with the given
* initial capacity and the given load factor.
*
* @param initialCapacity
* The initial capacity of the <tt>WeakIdentityHashMap</tt>
* @param loadFactor
* The load factor of the <tt>WeakIdentityHashMap</tt>
* @throws IllegalArgumentException
* If the initial capacity is negative, or if the load factor is
* nonpositive.
*/
public WeakIdentityHashMap(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 <tt>WeakIdentityHashMap</tt> with the given
* initial capacity and the default load factor, which is <tt>0.75</tt>.
*
* @param initialCapacity
* The initial capacity of the <tt>WeakIdentityHashMap</tt>
* @throws IllegalArgumentException
* If the initial capacity is negative.
*/
public WeakIdentityHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs a new, empty <tt>WeakIdentityHashMap</tt> with the default
* initial capacity (16) and the default load factor (0.75).
*/
public WeakIdentityHashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR;
threshold = DEFAULT_INITIAL_CAPACITY;
table = new Entry[DEFAULT_INITIAL_CAPACITY];
}
/**
* Constructs a new <tt>WeakIdentityHashMap</tt> with the same mappings as
* the specified <tt>Map</tt>. The <tt>WeakIdentityHashMap</tt> is
* created with default load factor, which is <tt>0.75</tt> and an initial
* capacity sufficient to hold the mappings in the specified <tt>Map</tt>.
*
* @param t
* the map whose mappings are to be placed in this map.
* @throws NullPointerException
* if the specified map is null.
*/
public WeakIdentityHashMap(Map t) {
this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1, 16), DEFAULT_LOAD_FACTOR);
putAll(t);
}
// 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);
}
/**
* Return internal representation of null key back to caller as null
*/
private static Object unmaskNull(Object key) {
return (key == NULL_KEY ? null : key);
}
/**
* Return a hash code for non-null Object x.
*/
int hash(Object x) {
int h = System.identityHashCode(x);
return h - (h << 7); // that is,, -127 * h
}
/**
* Return index for hash code h.
*/
static int indexFor(int h, int length) {
return h & (length - 1);
}
/**
* Expunge stale entries from the table.
*/
private void expungeStaleEntries() {
Object r;
while ((r = queue.poll()) != null) {
Entry e = (Entry) r;
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;
}
}
}
/**
* Return 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 <tt>true</tt> 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.
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns the value to which the specified key is mapped in this weak hash
* map, or <tt>null</tt> if the map contains no mapping for this key. A
* return value of <tt>null</tt> does not <i>necessarily</i> indicate that
* the map contains no mapping for the key; it is also possible that the map
* explicitly maps the key to <tt>null</tt>. The <tt>containsKey</tt>
* method may be used to distinguish these two cases.
*
* @param key
* the key whose associated value is to be returned.
* @return the value to which this map maps the specified key, or
* <tt>null</tt> if the map contains no mapping for this key.
* @see #put(Object, Object)
*/
public Object get(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
Entry e = tab[index];
while (e != null) {
if (e.hash == h && k == e.get())
return e.value;
e = e.next;
}
return null;
}
/**
* Returns <tt>true</tt> if this map contains a mapping for the specified
* key.
*
* @param key
* The key whose presence in this map is to be tested
* @return <tt>true</tt> if there is a mapping for <tt>key</tt>;
* <tt>false</tt> otherwise
*/
public boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Returns the entry associated with the specified key in the HashMap. Returns
* null if the HashMap contains no mapping for this key.
*/
Entry getEntry(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int index = indexFor(h, tab.length);
Entry e = tab[index];
while (e != null && !(e.hash == h && 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 previous value associated with specified key, or <tt>null</tt> if
* there was no mapping for key. A <tt>null</tt> return can also
* indicate that the HashMap previously associated <tt>null</tt>
* with the specified key.
*/
public Object put(Object key, Object value) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
for (Entry e = tab[i]; e != null; e = e.next) {
if (h == e.hash && k == e.get()) {
Object oldValue = e.value;
if (value != oldValue)
e.value = value;
return oldValue;
}
}
modCount++;
tab[i] = new Entry(k, value, queue, h, tab[i]);
if (++size >= threshold)
resize(tab.length * 2);
return null;
}
/**
* Rehashes the contents of this map into a new <tt>HashMap</tt> instance
* with a larger capacity. This method is called automatically when the number
* of keys in this map exceeds its capacity and load factor.
*
* Note that this method is a no-op if it's called with newCapacity ==
* 2*MAXIMUM_CAPACITY (which is Integer.MIN_VALUE).
*
* @param newCapacity
* the new capacity, MUST be a power of two.
*/
void resize(int newCapacity) {
// assert (newCapacity & -newCapacity) == newCapacity; // power of 2
Entry[] oldTable = getTable();
int oldCapacity = oldTable.length;
// check if needed
if (size < threshold || oldCapacity > newCapacity)
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;
}
}
/** Transfer all entries from src to dest tables */
private void transfer(Entry[] src, Entry[] dest) {
for (int j = 0; j < src.length; ++j) {
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.
* <p>
*
* @param t
* mappings to be stored in this map.
* @throws NullPointerException
* if the specified map is null.
*/
public void putAll(Map t) {
// Expand enough to hold t's elements without resizing.
int n = t.size();
if (n == 0)
return;
if (n >= threshold) {
n = (int) (n / loadFactor + 1);
if (n > MAXIMUM_CAPACITY)
n = MAXIMUM_CAPACITY;
int capacity = table.length;
while (capacity < n)
capacity <<= 1;
resize(capacity);
}
for (Iterator i = t.entrySet().iterator(); i.hasNext();) {
Map.Entry e = (Map.Entry) i.next();
put(e.getKey(), e.getValue());
}
}
/**
* Removes the mapping for this key from this map if present.
*
* @param key
* key whose mapping is to be removed from the map.
* @return previous value associated with specified key, or <tt>null</tt> if
* there was no mapping for key. A <tt>null</tt> return can also
* indicate that the map previously associated <tt>null</tt> with
* the specified key.
*/
public Object remove(Object key) {
Object k = maskNull(key);
int h = hash(k);
Entry[] tab = getTable();
int i = indexFor(h, tab.length);
Entry prev = tab[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (h == e.hash && 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 = hash(k);
int i = indexFor(h, tab.length);
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 mappings from this map.
*/
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 <tt>true</tt> 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 <tt>true</tt> 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 Object value;
private final int hash;
private Entry next;
/**
* Create new entry.
*/
Entry(Object key, Object value, ReferenceQueue queue, int hash, Entry next) {
super(key, queue);
this.value = value;
this.hash = hash;
this.next = next;
}
public Object getKey() {
return unmaskNull(this.get());
}
public Object getValue() {
return value;
}
public Object setValue(Object newValue) {
Object 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) {
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 : System.identityHashCode(k)) ^ (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;
}
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();
WeakIdentityHashMap.this.remove(currentKey);
expectedModCount = modCount;
lastReturned = null;
currentKey = null;
}
}
private class ValueIterator extends HashIterator {
public Object next() {
return nextEntry().value;
}
}
private class KeyIterator extends HashIterator {
public Object next() {
return nextEntry().getKey();
}
}
private class EntryIterator extends HashIterator {
public Object next() {
return nextEntry();
}
}
// Views
private transient Set entrySet = null;
/**
* Returns a set view of the keys contained in this map. The set is backed by
* the map, so changes to the map are reflected in the set, and vice-versa.
* The set supports element removal, which removes the corresponding mapping
* from this map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
* operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
* operations.
*
* @return a set view of the keys contained in this map.
*/
public Set keySet() {
Set ks = keySet;
return (ks != null ? ks : (keySet = new KeySet()));
}
private class KeySet extends AbstractSet {
public Iterator iterator() {
return new KeyIterator();
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
if (containsKey(o)) {
WeakIdentityHashMap.this.remove(o);
return true;
} else
return false;
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(i.next());
return c.toArray();
}
public Object[] toArray(Object a[]) {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(i.next());
return c.toArray(a);
}
}
/**
* Returns a collection view of the values contained in this map. The
* collection is backed by the map, so changes to the map are reflected in the
* collection, and vice-versa. The collection supports element removal, which
* removes the corresponding mapping from this map, via the
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
* operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
* operations.
*
* @return a collection view of the values contained in this map.
*/
public Collection values() {
Collection vs = values;
return (vs != null ? vs : (values = new Values()));
}
private class Values extends AbstractCollection {
public Iterator iterator() {
return new ValueIterator();
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public boolean contains(Object o) {
return containsValue(o);
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(i.next());
return c.toArray();
}
public Object[] toArray(Object a[]) {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(i.next());
return c.toArray(a);
}
}
/**
* Returns a collection view of the mappings contained in this map. Each
* element in the returned collection is a <tt>Map.Entry</tt>. 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 the map, via the
* <tt>Iterator.remove</tt>, <tt>Collection.remove</tt>,
* <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
* operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
* operations.
*
* @return a collection view of the mappings contained in this map.
* @see java.util.Map.Entry
*/
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);
}
public boolean remove(Object o) {
return removeMapping(o) != null;
}
public int size() {
return WeakIdentityHashMap.this.size();
}
public void clear() {
WeakIdentityHashMap.this.clear();
}
public Object[] toArray() {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(new SimpleEntry((Map.Entry) i.next()));
return c.toArray();
}
public Object[] toArray(Object a[]) {
Collection c = new ArrayList(size());
for (Iterator i = iterator(); i.hasNext();)
c.add(new SimpleEntry((Map.Entry) i.next()));
return c.toArray(a);
}
}
static class SimpleEntry implements Map.Entry {
Object key;
Object value;
public SimpleEntry(Object key, Object value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Map.Entry e) {
this.key = e.getKey();
this.value = e.getValue();
}
public Object getKey() {
return key;
}
public Object getValue() {
return value;
}
public Object setValue(Object value) {
Object oldValue = this.value;
this.value = value;
return oldValue;
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry) o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
public int hashCode() {
return ((key == null) ? 0 : key.hashCode()) ^ ((value == null) ? 0 : value.hashCode());
}
public String toString() {
return key + "=" + value;
}
private static boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
}
}
]]>