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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.openjpa.lib.util.concurrent;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.Set;
import org.apache.openjpa.lib.util.SizedMap;
/**
* This class implements a HashMap which has limited synchronization.
* In particular mutators are generally synchronized while accessors
* are generally not. Additionally the Iterators returned by this
* class are not "fail-fast", but instead try to continue to iterate
* over the data structure after changes have been made.
* The synchronization semantics are built right in to the
* implementation rather than using a delegating wrapper like the
* other collection classes do because it wasn't clear to me that the
* how the two should be seperated or that it would be useful to do
* so. This can probably be a topic for further debate in the future.
* This class is based heavily on the HashMap class in the Java
* collections package.
*/
public class ConcurrentHashMap extends AbstractMap
implements ConcurrentMap, SizedMap, Cloneable, Serializable {
/**
* 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;
/**
* Cache of random numbers used in "random" methods, since generating them
* is expensive. We hope each map changes enough between cycling through
* this list that the overall effect is random enough.
*/
static final double[] RANDOMS = new double[1000];
static {
Random random = new Random();
for (int i = 0; i < RANDOMS.length; i++)
RANDOMS[i] = random.nextDouble();
}
/**
* The table, resized as necessary. Length MUST Always be a power of two.
*/
private transient Entry[] table;
/**
* The number of key-value mappings contained in this identity hash map.
*/
private transient int size;
/**
* The next size value at which to resize(capacity * load factor).
*
* @serial
*/
private int threshold;
/**
* The load factor for the hash table.
*
* @serial
*/
private final float loadFactor;
/**
* Spread "random" removes and iteration.
*/
private int randomEntry = 0;
/**
* Maximum entries.
*/
private int maxSize = Integer.MAX_VALUE;
/**
* Constructs an empty ConcurrentHashMap with the specified initial
* capacity and load factor.
*
* @param initialCapacity The initial capacity.
* @param loadFactor The load factor.
* @throws IllegalArgumentException if the initial capacity is negative
* or the load factor is nonpositive.
*/
public ConcurrentHashMap(int initialCapacity, float loadFactor) {
if (initialCapacity < 0) {
throw new IllegalArgumentException("Illegal initial capacity: " +
initialCapacity);
}
if (initialCapacity > MAXIMUM_CAPACITY)
initialCapacity = MAXIMUM_CAPACITY;
if (loadFactor <= 0 || loadFactor > 1) {
throw new IllegalArgumentException("Illegal load factor: " +
loadFactor);
}
// Find a power of 2 >= initialCapacity
int capacity = 1;
while (capacity < initialCapacity) capacity <<= 1;
this.loadFactor = loadFactor;
threshold = (int) (capacity * loadFactor);
table = new Entry[capacity];
}
/**
* Constructs an empty ConcurrentHashMap with the specified initial
* capacity and the default load factor(0.75).
*
* @param initialCapacity the initial capacity.
* @throws IllegalArgumentException if the initial capacity is negative.
*/
public ConcurrentHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs an empty ConcurrentHashMap with the default initial
* capacity(16) and the default load factor(0.75).
*/
public ConcurrentHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs a new ConcurrentHashMap with the same mappings as the
* specified Map. The ConcurrentHashMap is created with
* 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.
*/
public ConcurrentHashMap(Map m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR);
putAll(m);
}
// internal utilities
/**
* Value representing null keys inside tables.
*/
private static final Object NULL_KEY = new Object();
/**
* Returns internal representation for key. Use NULL_KEY if key is null.
*/
private static Object maskNull(Object key) {
return (key == null ? NULL_KEY : key);
}
/**
* Returns key represented by specified internal representation.
*/
private static Object unmaskNull(Object key) {
return (key == NULL_KEY ? null : key);
}
/**
* Returns a hash code for non-null Object x.
*/
private static int hash(Object x) {
int h = x.hashCode();
return h - (h << 7); // i.e., -127 * h
}
/**
* Check for equality of non-null reference x and possibly-null y.
*/
private static boolean eq(Object x, Object y) {
return x == y || x.equals(y);
}
/**
* Returns the current capacity of backing table in this map.
*
* @return the current capacity of backing table in this map.
*/
public final int capacity() {
return table.length;
}
/**
* Returns the load factor for this map.
*
* @return the load factor for this map.
*/
public final float loadFactor() {
return loadFactor;
}
@Override
public int getMaxSize() {
return maxSize;
}
@Override
public void setMaxSize(int maxSize) {
this.maxSize = (maxSize < 0) ? Integer.MAX_VALUE : maxSize;
if (this.maxSize != Integer.MAX_VALUE)
removeOverflow(this.maxSize);
}
@Override
public boolean isFull() {
return maxSize != Integer.MAX_VALUE && size() >= maxSize;
}
@Override
public void overflowRemoved(Object key, Object value) {
}
/**
* Returns the number of key-value mappings in this map.
*
* @return the number of key-value mappings in this map.
*/
@Override
public final int size() {
return size;
}
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings.
*/
@Override
public final boolean isEmpty() {
return size == 0;
}
/**
* Returns the value to which the specified key is mapped in this identity
* hash map, or null if the map contains no mapping for this key.
* A return value of null does not necessarily indicate
* that the map contains no mapping for the key; it is also possible that
* the map explicitly maps the key to null. The
* containsKey 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
* null if the map contains no mapping for this key.
* @see #put(Object, Object)
*/
@Override
public Object get(Object key) {
Entry e = getEntry(key);
return e == null ? null : e.value;
}
/**
* 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 this map contains a mapping for the specified
* key.
*/
@Override
public final boolean containsKey(Object key) {
return getEntry(key) != null;
}
/**
* Returns the entry associated with the specified key in the
* ConcurrentHashMap. Returns null if the ConcurrentHashMap contains no
* mapping for this key.
*/
protected Entry getEntry(Object key) {
Object k = maskNull(key);
int hash = hash(k);
Entry[] tab = table;
for (Entry e = tab[hash & (tab.length - 1)]; e != null; e = e.next) {
if (e.hash == hash && eq(k, e.key)) return e;
}
return null;
}
/**
* 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 null
* if there was no mapping for key. A null return can
* also indicate that the ConcurrentHashMap previously associated
* null with the specified key.
*/
@Override
public Object put(Object key, Object value) {
Object k = maskNull(key);
int hash = hash(k);
synchronized (this) {
int i = hash & (table.length - 1);
for (Entry e = table[i]; e != null; e = e.next) {
if (e.hash == hash && eq(k, e.key)) {
Object oldValue = e.value;
e.value = value;
return oldValue;
}
}
if (maxSize != Integer.MAX_VALUE)
removeOverflow(maxSize - 1);
table[i] = createEntry(hash, k, value, table[i]);
if (size++ >= threshold) resize(2 * table.length);
}
return null;
}
/**
* Remove any entries equal to or over the max size.
*/
private void removeOverflow(int maxSize) {
while (size > maxSize) {
Map.Entry entry = removeRandom();
if (entry == null)
break;
overflowRemoved(entry.getKey(), entry.getValue());
}
}
@Override
public Object putIfAbsent(Object key, Object value) {
Object k = maskNull(key);
int hash = hash(k);
synchronized (this) {
int i = hash & (table.length - 1);
for (Entry e = table[i]; e != null; e = e.next) {
if (e.hash == hash && eq(k, e.key)) {
return e.value;
}
}
if (maxSize != Integer.MAX_VALUE)
removeOverflow(maxSize - 1);
table[i] = createEntry(hash, k, value, table[i]);
if (size++ >= threshold) resize(2 * table.length);
}
return null;
}
/**
* Rehashes the contents of this map into a new ConcurrentHashMap
* instance with a larger capacity. This method is called automatically when
* the number of keys in this map exceeds its capacity and load factor.
*
* @param newCapacity the new capacity, MUST be a power of two.
*/
private void resize(int newCapacity) {
// assert(newCapacity & -newCapacity) == newCapacity; // power of 2
Entry[] oldTable = table;
int oldCapacity = oldTable.length;
// check if needed
if (size < threshold || oldCapacity > newCapacity) return;
Entry[] newTable = new Entry[newCapacity];
int mask = newCapacity - 1;
for (int i = oldCapacity; i-- > 0;) {
for (Entry e = oldTable[i]; e != null; e = e.next) {
Entry clone = (Entry) e.clone();
int j = clone.hash & mask;
clone.next = newTable[j];
newTable[j] = clone;
}
}
table = newTable;
threshold = (int) (newCapacity * loadFactor);
}
/**
* 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 t mappings to be stored in this map.
* @throws NullPointerException if the specified map is null.
*/
@Override
public final synchronized 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 null
* if there was no mapping for key. A null return can
* also indicate that the map previously associated null
* with the specified key.
*/
@Override
public Object remove(Object key) {
Entry e = removeEntryForKey(key);
return (e == null ? e : e.value);
}
/**
* Removes and returns the entry associated with the specified key in the
* ConcurrentHashMap. Returns null if the ConcurrentHashMap contains no
* mapping for this key.
*/
private Entry removeEntryForKey(Object key) {
Object k = maskNull(key);
int hash = hash(k);
synchronized (this) {
int i = hash & (table.length - 1);
Entry e = table[i];
if (e == null) return null;
if (e.hash == hash && eq(k, e.key)) {
size--;
table[i] = e.next;
return e;
}
Entry prev = e;
for (e = e.next; e != null; prev = e, e = e.next) {
if (e.hash == hash && eq(k, e.key)) {
size--;
prev.next = e.next;
return e;
}
}
}
return null;
}
/**
* Special version of remove for EntrySet.
*/
private Entry removeMapping(Object o) {
if (!(o instanceof Map.Entry)) return null;
Map.Entry entry = (Map.Entry) o;
Object k = maskNull(entry.getKey());
int hash = hash(k);
synchronized (this) {
int i = hash & (table.length - 1);
Entry e = table[i];
if (e == null) return null;
if (e.hash == hash && e.equals(entry)) {
size--;
table[i] = e.next;
return e;
}
Entry prev = e;
for (e = e.next; e != null; prev = e, e = e.next) {
if (e.hash == hash && e.equals(entry)) {
size--;
prev.next = e.next;
return e;
}
}
}
return null;
}
/**
* Removes all mappings from this map.
*/
@Override
public synchronized void clear() {
table = new Entry[table.length];
size = 0;
}
/**
* Return an arbitrary entry index.
*/
private int randomEntryIndex() {
if (randomEntry == RANDOMS.length)
randomEntry = 0;
return (int) (RANDOMS[randomEntry++] * table.length);
}
@Override
public Map.Entry removeRandom() {
if (size == 0)
return null;
synchronized (this) {
int random = randomEntryIndex();
int index = findEntry(random, random % 2 == 0, false);
if (index == -1)
return null;
Entry rem = table[index];
table[index] = rem.next;
size--;
return rem;
}
}
/**
* Find the index of the entry nearest the given index, starting in the
* given direction.
*/
private int findEntry(int start, boolean forward, boolean searchedOther) {
if (forward) {
for (int i = start; i < table.length; i++)
if (table[i] != null)
return i;
return (searchedOther || start == 0) ? -1
: findEntry(start - 1, false, true);
} else {
for (int i = start; i >= 0; i--)
if (table[i] != null)
return i;
return (searchedOther || start == table.length - 1) ? -1
: findEntry(start + 1, true, true);
}
}
@Override
public Iterator randomEntryIterator() {
// pass index so calculated before iterator refs table, in case table
// gets replace with a larger one
return new HashIterator(ENTRIES, randomEntryIndex());
}
/**
* 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.
*/
@Override
public final boolean containsValue(Object value) {
if (value == null) return containsNullValue();
Entry tab[] = table;
for (int i = 0; i < tab.length; i++) {
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[] = table;
for (int i = 0; i < tab.length; i++) {
for (Entry e = tab[i]; e != null; e = e.next) {
if (e.value == null) return true;
}
}
return false;
}
/**
* Returns a shallow copy of this ConcurrentHashMap instance: the
* keys and values themselves are not cloned.
*
* @return a shallow copy of this map.
*/
@Override
public final Object clone() {
return new ConcurrentHashMap(this);
}
protected Entry createEntry(int h, Object k, Object v, Entry n) {
return new Entry(h, k, v, n);
}
protected static class Entry implements Map.Entry {
final Object key;
Object value;
final int hash;
Entry next;
/**
* Create new entry.
*/
protected Entry(int h, Object k, Object v, Entry n) {
value = v;
next = n;
key = k;
hash = h;
}
@Override
public Object getKey() {
return unmaskNull(key);
}
@Override
public Object getValue() {
return value;
}
@Override
public Object setValue(Object newValue) {
Object oldValue = value;
value = newValue;
return oldValue;
}
@Override
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;
}
@Override
public int hashCode() {
return (key == NULL_KEY ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
@Override
public String toString() {
return getKey() + "=" + getValue();
}
@Override
protected Object clone() {
// It is the callers responsibility to set the next field
// correctly.
return new Entry(hash, key, value, null);
}
}
// Types of Enumerations/Iterations
private static final int KEYS = 0;
private static final int VALUES = 1;
private static final int ENTRIES = 2;
/**
* Map iterator.
*/
private class HashIterator implements Iterator {
final Entry[] table = ConcurrentHashMap.this.table;
final int type;
int startIndex;
int stopIndex = 0;
int index;
Entry entry = null;
Entry lastReturned = null;
HashIterator(int type, int startIndex) {
this.type = type;
this.startIndex = startIndex;
index = startIndex;
}
@Override
public boolean hasNext() {
if (entry != null) {
return true;
}
while (index >= stopIndex) {
if ((entry = table[index--]) != null) {
return true;
}
}
if (stopIndex == 0) {
index = table.length - 1;
stopIndex = startIndex + 1;
while (index >= stopIndex) {
if ((entry = table[index--]) != null) {
return true;
}
}
}
return false;
}
@Override
public Object next() {
if (!hasNext())
throw new NoSuchElementException();
Entry e = lastReturned = entry;
entry = e.next;
return type == KEYS ? e.key : (type == VALUES ? e.value : e);
}
@Override
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
synchronized (ConcurrentHashMap.this) {
Entry[] tab = ConcurrentHashMap.this.table;
int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index], prev = null; e != null;
prev = e, e = e.next) {
if (e == lastReturned) {
if (prev == null)
tab[index] = e.next;
else
prev.next = e.next;
size--;
lastReturned = null;
return;
}
}
throw new Error("Iterated off table when doing remove");
}
}
}
// Views
private transient Set entrySet = null;
private transient Set keySet = null;
private transient Collection values = 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 Iterator.remove,
* Set.remove, removeAll, retainAll, and
* clear operations. It does not support the add or
* addAll operations.
*
* @return a set view of the keys contained in this map.
*/
@Override
public final Set keySet() {
Set ks = keySet;
return (ks != null ? ks : (keySet = new KeySet()));
}
private final class KeySet extends AbstractSet {
@Override
public Iterator iterator() {
return new HashIterator(KEYS, table.length - 1);
}
@Override
public int size() {
return size;
}
@Override
public boolean contains(Object o) {
return containsKey(o);
}
@Override
public boolean remove(Object o) {
return ConcurrentHashMap.this.removeEntryForKey(o) != null;
}
@Override
public void clear() {
ConcurrentHashMap.this.clear();
}
}
/**
* 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
* Iterator.remove, Collection.remove,
* removeAll, retainAll, and clear operations.
* It does not support the add or addAll operations.
*
* @return a collection view of the values contained in this map.
*/
@Override
public final Collection values() {
Collection vs = values;
return (vs != null ? vs : (values = new Values()));
}
private final class Values extends AbstractCollection {
@Override
public Iterator iterator() {
return new HashIterator(VALUES, table.length - 1);
}
@Override
public int size() {
return size;
}
@Override
public boolean contains(Object o) {
return containsValue(o);
}
@Override
public void clear() {
ConcurrentHashMap.this.clear();
}
}
/**
* Returns a collection view of the mappings contained in this map. Each
* element in the returned collection is a Map.Entry. 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
* Iterator.remove, Collection.remove,
* removeAll, retainAll, and clear operations.
* It does not support the add or addAll operations.
*
* @return a collection view of the mappings contained in this map.
* @see Map.Entry
*/
@Override
public final Set entrySet() {
Set es = entrySet;
return (es != null ? es : (entrySet = new EntrySet()));
}
private final class EntrySet extends AbstractSet {
@Override
public Iterator iterator() {
return new HashIterator(ENTRIES, table.length - 1);
}
@Override
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 size;
}
@Override
public void clear() {
ConcurrentHashMap.this.clear();
}
}
/**
* Save the state of the ConcurrentHashMap instance to a stream
* (i.e., serialize it).
*
* @serialData The capacity of the ConcurrentHashMap(the length of
* the bucket array) is emitted(int), followed by the size of the
* ConcurrentHashMap(the number of key-value mappings), followed by the key
* (Object) and value(Object) for each key-value mapping represented by the
* ConcurrentHashMap The key-value mappings are emitted in the order that
* they are returned by entrySet().iterator().
*/
private void writeObject(ObjectOutputStream s) throws IOException {
// Write out the threshold, loadfactor, and any hidden stuff
s.defaultWriteObject();
// Write out number of buckets
s.writeInt(table.length);
// Write out size(number of Mappings)
s.writeInt(size);
s.writeInt(maxSize);
// Write out keys and values(alternating)
for (Iterator i = entrySet().iterator(); i.hasNext();) {
Map.Entry e = (Map.Entry) i.next();
s.writeObject(e.getKey());
s.writeObject(e.getValue());
}
}
private static final long serialVersionUID = -6452706556724125778L;
/**
* Reconstitute the ConcurrentHashMap instance from a stream(i.e.,
* deserialize it).
*/
private void readObject(ObjectInputStream s)
throws IOException, ClassNotFoundException {
// Read in the threshold, loadfactor, and any hidden stuff
s.defaultReadObject();
// Read in number of buckets and allocate the bucket array;
int numBuckets = s.readInt();
table = new Entry[numBuckets];
// Read in size(number of Mappings)
int size = s.readInt();
// read the max size
maxSize = s.readInt();
// Read the keys and values, and put the mappings in the
// ConcurrentHashMap
for (int i = 0; i < size; i++) {
Object key = s.readObject();
Object value = s.readObject();
put(key, value);
}
}
}
