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android / platform / dalvik / 89efc3d632adfa076bd622369b1ad8e4b49cf20e / . / libcore / concurrent / src / main / java / java / util / concurrent / ConcurrentHashMap.java
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/*
* 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 java.util.concurrent;
import java.util.concurrent.locks.*;
import java.util.*;
import java.io.Serializable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
// BEGIN android-note
// removed link to collections framework docs
// removed cloneable interface from ConcurrentMap interface
// END android-note
/**
* A hash table supporting full concurrency of retrievals and
* adjustable expected concurrency for updates. This class obeys the
* same functional specification as {@link java.util.Hashtable}, and
* includes versions of methods corresponding to each method of
* <tt>Hashtable</tt>. 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 <tt>Hashtable</tt> in programs that rely on its
* thread safety but not on its synchronization details.
*
* <p> Retrieval operations (including <tt>get</tt>) generally do not
* block, so may overlap with update operations (including
* <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results
* of the most recently <em>completed</em> update operations holding
* upon their onset. For aggregate operations such as <tt>putAll</tt>
* and <tt>clear</tt>, 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 <tt>concurrencyLevel</tt> constructor argument
* (default 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.
*
* <p>This class implements all of the <em>optional</em> methods
* of the {@link Map} and {@link Iterator} interfaces.
*
* <p> Like {@link java.util.Hashtable} but unlike {@link
* java.util.HashMap}, this class does NOT allow <tt>null</tt> to be
* used as a key or value.
*
* @since 1.5
* @author Doug Lea
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
*/
public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
implements ConcurrentMap<K, V>, Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/*
* The basic strategy is to subdivide the table among Segments,
* each of which itself is a concurrently readable hash table.
*/
/* ---------------- Constants -------------- */
/**
* The default initial number of table slots for this table.
* Used when not otherwise specified in constructor.
*/
static 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 to ensure that entries are indexible
* using ints.
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The default load factor for this table. Used when not
* otherwise specified in constructor.
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The default number of concurrency control segments.
**/
static final int DEFAULT_SEGMENTS = 16;
/**
* The maximum number of segments to allow; used to bound
* constructor arguments.
*/
static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
/* ---------------- 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[] segments;
transient Set<K> keySet;
transient Set<Map.Entry<K,V>> entrySet;
transient Collection<V> values;
/* ---------------- Small Utilities -------------- */
/**
* Returns a hash code for non-null Object x.
* Uses the same hash code spreader as most other java.util hash tables.
* @param x the object serving as a key
* @return the hash code
*/
static int hash(Object x) {
int h = x.hashCode();
h += ~(h << 9);
h ^= (h >>> 14);
h += (h << 4);
h ^= (h >>> 10);
return h;
}
/**
* 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 (Segment<K,V>) segments[(hash >>> segmentShift) & segmentMask];
}
/* ---------------- Inner Classes -------------- */
/**
* Segments are specialized versions of hash tables. This
* subclasses from ReentrantLock opportunistically, just to
* simplify some locking and avoid separate construction.
**/
static final class Segment<K,V> extends ReentrantLock implements Serializable {
/*
* 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 a memory barrier to ensure that completed write
* operations performed by other threads are
* noticed. Conveniently, the "count" field, tracking the
* number of elements, can also serve as the volatile variable
* providing proper read/write barriers. This is convenient
* because this field needs to be read in many read operations
* anyway.
*
* Implementors note. The basic rules for all this are:
*
* - 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 updating. 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 are marked
* in code comments.
*/
private static final long serialVersionUID = 2249069246763182397L;
/**
* The number of elements in this segment's region.
**/
transient volatile int count;
/**
* Number of updates; used for checking lack of modifications
* in bulk-read methods.
*/
transient int modCount;
/**
* The table is rehashed when its size exceeds this threshold.
* (The value of this field is always (int)(capacity *
* loadFactor).)
*/
transient int threshold;
/**
* The per-segment table
*/
transient HashEntry[] 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;
Segment(int initialCapacity, float lf) {
loadFactor = lf;
setTable(new HashEntry[initialCapacity]);
}
/**
* Set table to new HashEntry array.
* Call only while holding lock or in constructor.
**/
void setTable(HashEntry[] newTable) {
table = newTable;
threshold = (int)(newTable.length * loadFactor);
count = count; // write-volatile
}
/* Specialized implementations of map methods */
V get(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
while (e != null) {
if (e.hash == hash && key.equals(e.key))
return e.value;
e = e.next;
}
}
return null;
}
boolean containsKey(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> e = (HashEntry<K,V>) tab[index];
while (e != null) {
if (e.hash == hash && key.equals(e.key))
return true;
e = e.next;
}
}
return false;
}
boolean containsValue(Object value) {
if (count != 0) { // read-volatile
HashEntry[] tab = table;
int len = tab.length;
for (int i = 0 ; i < len; i++)
for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i] ; e != null ; e = e.next)
if (value.equals(e.value))
return true;
}
return false;
}
boolean replace(K key, int hash, V oldValue, V newValue) {
lock();
try {
int c = count;
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
HashEntry<K,V> e = first;
for (;;) {
if (e == null)
return false;
if (e.hash == hash && key.equals(e.key))
break;
e = e.next;
}
V v = e.value;
if (v == null || !oldValue.equals(v))
return false;
e.value = newValue;
count = c; // write-volatile
return true;
} finally {
unlock();
}
}
V replace(K key, int hash, V newValue) {
lock();
try {
int c = count;
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
HashEntry<K,V> e = first;
for (;;) {
if (e == null)
return null;
if (e.hash == hash && key.equals(e.key))
break;
e = e.next;
}
V v = e.value;
e.value = newValue;
count = c; // write-volatile
return v;
} finally {
unlock();
}
}
V put(K key, int hash, V value, boolean onlyIfAbsent) {
lock();
try {
int c = count;
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> first = (HashEntry<K,V>) tab[index];
for (HashEntry<K,V> e = first; e != null; e = (HashEntry<K,V>) e.next) {
if (e.hash == hash && key.equals(e.key)) {
V oldValue = e.value;
if (!onlyIfAbsent)
e.value = value;
++modCount;
count = c; // write-volatile
return oldValue;
}
}
tab[index] = new HashEntry<K,V>(hash, key, value, first);
++modCount;
++c;
count = c; // write-volatile
if (c > threshold)
setTable(rehash(tab));
return null;
} finally {
unlock();
}
}
HashEntry[] rehash(HashEntry[] oldTable) {
int oldCapacity = oldTable.length;
if (oldCapacity >= MAXIMUM_CAPACITY)
return oldTable;
/*
* 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.
*/
HashEntry[] newTable = new HashEntry[oldCapacity << 1];
int sizeMask = newTable.length - 1;
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.
HashEntry<K,V> e = (HashEntry<K,V>)oldTable[i];
if (e != null) {
HashEntry<K,V> next = e.next;
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) {
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) {
int k = p.hash & sizeMask;
newTable[k] = new HashEntry<K,V>(p.hash,
p.key,
p.value,
(HashEntry<K,V>) newTable[k]);
}
}
}
}
return newTable;
}
/**
* Remove; match on key only if value null, else match both.
*/
V remove(Object key, int hash, Object value) {
lock();
try {
int c = count;
HashEntry[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K,V> first = (HashEntry<K,V>)tab[index];
HashEntry<K,V> e = first;
for (;;) {
if (e == null)
return null;
if (e.hash == hash && key.equals(e.key))
break;
e = e.next;
}
V oldValue = e.value;
if (value != null && !value.equals(oldValue))
return null;
// All entries following removed node can stay in list, but
// all preceding ones need to be cloned.
HashEntry<K,V> newFirst = e.next;
for (HashEntry<K,V> p = first; p != e; p = p.next)
newFirst = new HashEntry<K,V>(p.hash, p.key,
p.value, newFirst);
tab[index] = newFirst;
++modCount;
count = c-1; // write-volatile
return oldValue;
} finally {
unlock();
}
}
void clear() {
lock();
try {
HashEntry[] tab = table;
for (int i = 0; i < tab.length ; i++)
tab[i] = null;
++modCount;
count = 0; // write-volatile
} finally {
unlock();
}
}
}
/**
* ConcurrentHashMap list entry. Note that this is never exported
* out as a user-visible Map.Entry
*/
static final class HashEntry<K,V> {
final K key;
V value;
final int hash;
final HashEntry<K,V> next;
HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
this.value = value;
this.hash = hash;
this.key = key;
this.next = next;
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the specified initial
* capacity and the specified load factor.
*
* @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.
* @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 ConcurrentHashMap(int initialCapacity,
float loadFactor, int concurrencyLevel) {
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
throw new IllegalArgumentException();
if (concurrencyLevel > MAX_SEGMENTS)
concurrencyLevel = MAX_SEGMENTS;
// Find power-of-two sizes best matching arguments
int sshift = 0;
int ssize = 1;
while (ssize < concurrencyLevel) {
++sshift;
ssize <<= 1;
}
segmentShift = 32 - sshift;
segmentMask = ssize - 1;
this.segments = new Segment[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;
for (int i = 0; i < this.segments.length; ++i)
this.segments[i] = new Segment<K,V>(cap, loadFactor);
}
/**
* Creates a new, empty map with the specified initial
* capacity, and with default load factor and concurrencyLevel.
*
* @param initialCapacity The implementation performs internal
* sizing to accommodate this many elements.
* @throws IllegalArgumentException if the initial capacity of
* elements is negative.
*/
public ConcurrentHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
}
/**
* Creates a new, empty map with a default initial capacity,
* load factor, and concurrencyLevel.
*/
public ConcurrentHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
}
/**
* Creates a new map with the same mappings as the given map. The
* map is created with a capacity of twice the number of mappings in
* the given map or 11 (whichever is greater), and a default load factor.
* @param t the map
*/
public ConcurrentHashMap(Map<? extends K, ? extends V> t) {
this(Math.max((int) (t.size() / DEFAULT_LOAD_FACTOR) + 1,
11),
DEFAULT_LOAD_FACTOR, DEFAULT_SEGMENTS);
putAll(t);
}
// inherit Map javadoc
public boolean isEmpty() {
final Segment[] segments = this.segments;
/*
* We need to 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.
*/
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;
}
// inherit Map javadoc
public int size() {
final Segment[] segments = this.segments;
int[] mc = new int[segments.length];
for (;;) {
long sum = 0;
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
sum += segments[i].count;
mcsum += mc[i] = segments[i].modCount;
}
int check = 0;
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) {
if (sum > Integer.MAX_VALUE)
return Integer.MAX_VALUE;
else
return (int)sum;
}
}
}
/**
* Returns the value to which the specified key is mapped in this table.
*
* @param key a key in the table.
* @return the value to which the key is mapped in this table;
* <tt>null</tt> if the key is not mapped to any value in
* this table.
* @throws NullPointerException if the key is
* <tt>null</tt>.
*/
public V get(Object key) {
int hash = hash(key); // throws NullPointerException if key null
return segmentFor(hash).get(key, hash);
}
/**
* Tests if the specified object is a key in this table.
*
* @param key possible key.
* @return <tt>true</tt> if and only if the specified object
* is a key in this table, as determined by the
* <tt>equals</tt> method; <tt>false</tt> otherwise.
* @throws NullPointerException if the key is
* <tt>null</tt>.
*/
public boolean containsKey(Object key) {
int hash = hash(key); // throws NullPointerException if key null
return segmentFor(hash).containsKey(key, hash);
}
/**
* Returns <tt>true</tt> 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 <tt>containsKey</tt>.
*
* @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.
* @throws NullPointerException if the value is <tt>null</tt>.
*/
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
final Segment[] segments = this.segments;
int[] mc = new int[segments.length];
for (;;) {
int sum = 0;
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
int c = segments[i].count;
mcsum += mc[i] = segments[i].modCount;
if (segments[i].containsValue(value))
return true;
}
boolean cleanSweep = true;
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
int c = segments[i].count;
if (mc[i] != segments[i].modCount) {
cleanSweep = false;
break;
}
}
}
if (cleanSweep)
return false;
}
}
/**
* 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 <tt>true</tt> if and only if some key maps to the
* <tt>value</tt> argument in this table as
* determined by the <tt>equals</tt> method;
* <tt>false</tt> otherwise.
* @throws NullPointerException if the value is <tt>null</tt>.
*/
public boolean contains(Object value) {
return containsValue(value);
}
/**
* Maps the specified <tt>key</tt> to the specified
* <tt>value</tt> in this table. Neither the key nor the
* value can be <tt>null</tt>.
*
* <p> The value can be retrieved by calling the <tt>get</tt> method
* with a key that is equal to the original key.
*
* @param key the table key.
* @param value the value.
* @return the previous value of the specified key in this table,
* or <tt>null</tt> if it did not have one.
* @throws NullPointerException if the key or value is
* <tt>null</tt>.
*/
public V put(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).put(key, hash, value, false);
}
/**
* If the specified key is not already associated
* with a value, associate it with the given value.
* This is equivalent to
* <pre>
* if (!map.containsKey(key))
* return map.put(key, value);
* else
* return map.get(key);
* </pre>
* Except that the action is performed atomically.
* @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 map previously associated <tt>null</tt>
* with the specified key, if the implementation supports
* <tt>null</tt> values.
*
* @throws UnsupportedOperationException if the <tt>put</tt> operation is
* not supported by this map.
* @throws ClassCastException if the class of the specified key or value
* prevents it from being stored in this map.
* @throws NullPointerException if the specified key or value is
* <tt>null</tt>.
*
**/
public V putIfAbsent(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).put(key, hash, value, true);
}
/**
* 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 t Mappings to be stored in this map.
*/
public void putAll(Map<? extends K, ? extends V> t) {
for (Iterator<? extends Map.Entry<? extends K, ? extends V>> it = (Iterator<? extends Map.Entry<? extends K, ? extends V>>) t.entrySet().iterator(); it.hasNext(); ) {
Entry<? extends K, ? extends V> e = it.next();
put(e.getKey(), e.getValue());
}
}
/**
* Removes the key (and its corresponding value) from this
* table. This method does nothing if the key is not in the table.
*
* @param key the key that needs to be removed.
* @return the value to which the key had been mapped in this table,
* or <tt>null</tt> if the key did not have a mapping.
* @throws NullPointerException if the key is
* <tt>null</tt>.
*/
public V remove(Object key) {
int hash = hash(key);
return segmentFor(hash).remove(key, hash, null);
}
/**
* Remove entry for key only if currently mapped to given value.
* Acts as
* <pre>
* if (map.get(key).equals(value)) {
* map.remove(key);
* return true;
* } else return false;
* </pre>
* except that the action is performed atomically.
* @param key key with which the specified value is associated.
* @param value value associated with the specified key.
* @return true if the value was removed
* @throws NullPointerException if the specified key is
* <tt>null</tt>.
*/
public boolean remove(Object key, Object value) {
int hash = hash(key);
return segmentFor(hash).remove(key, hash, value) != null;
}
/**
* Replace entry for key only if currently mapped to given value.
* Acts as
* <pre>
* if (map.get(key).equals(oldValue)) {
* map.put(key, newValue);
* return true;
* } else return false;
* </pre>
* except that the action is performed atomically.
* @param key key with which the specified value is associated.
* @param oldValue value expected to be associated with the specified key.
* @param newValue value to be associated with the specified key.
* @return true if the value was replaced
* @throws NullPointerException if the specified key or values are
* <tt>null</tt>.
*/
public boolean replace(K key, V oldValue, V newValue) {
if (oldValue == null || newValue == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
* Replace entry for key only if currently mapped to some value.
* Acts as
* <pre>
* if ((map.containsKey(key)) {
* return map.put(key, value);
* } else return null;
* </pre>
* except that the action is performed atomically.
* @param key key with which the specified value is 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.
* @throws NullPointerException if the specified key or value is
* <tt>null</tt>.
*/
public V replace(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).replace(key, hash, value);
}
/**
* Removes all mappings from this map.
*/
public void clear() {
for (int i = 0; i < segments.length; ++i)
segments[i].clear();
}
// BEGIN android-removed
// /**
// * Returns a shallow copy of this
// * <tt>ConcurrentHashMap</tt> instance: the keys and
// * values themselves are not cloned.
// *
// * @return a shallow copy of this map.
// */
// public Object clone() {
// // We cannot call super.clone, since it would share final
// // segments array, and there's no way to reassign finals.
//
// float lf = segments[0].loadFactor;
// int segs = segments.length;
// int cap = (int)(size() / lf);
// if (cap < segs) cap = segs;
// ConcurrentHashMap<K,V> t = new ConcurrentHashMap<K,V>(cap, lf, segs);
// t.putAll(this);
// return t;
// }
// END android-changed
/**
* 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.
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
* will never throw {@link java.util.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 a set view of the keys contained in this map.
*/
public Set<K> keySet() {
Set<K> ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet());
}
/**
* 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.
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
* will never throw {@link java.util.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 a collection view of the values contained in this map.
*/
public Collection<V> values() {
Collection<V> vs = values;
return (vs != null) ? vs : (values = new Values());
}
/**
* 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.
* The returned <tt>iterator</tt> is a "weakly consistent" iterator that
* will never throw {@link java.util.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 a collection view of the mappings contained in this map.
*/
public Set<Map.Entry<K,V>> entrySet() {
Set<Map.Entry<K,V>> es = entrySet;
return (es != null) ? es : (entrySet = (Set<Map.Entry<K,V>>) (Set) new EntrySet());
}
/**
* 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();
}
/**
* 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();
}
/* ---------------- Iterator Support -------------- */
abstract class HashIterator {
int nextSegmentIndex;
int nextTableIndex;
HashEntry[] currentTable;
HashEntry<K, V> nextEntry;
HashEntry<K, V> lastReturned;
HashIterator() {
nextSegmentIndex = segments.length - 1;
nextTableIndex = -1;
advance();
}
public boolean hasMoreElements() { return hasNext(); }
final void advance() {
if (nextEntry != null && (nextEntry = nextEntry.next) != null)
return;
while (nextTableIndex >= 0) {
if ( (nextEntry = (HashEntry<K,V>)currentTable[nextTableIndex--]) != null)
return;
}
while (nextSegmentIndex >= 0) {
Segment<K,V> seg = (Segment<K,V>)segments[nextSegmentIndex--];
if (seg.count != 0) {
currentTable = seg.table;
for (int j = currentTable.length - 1; j >= 0; --j) {
if ( (nextEntry = (HashEntry<K,V>)currentTable[j]) != null) {
nextTableIndex = j - 1;
return;
}
}
}
}
}
public boolean hasNext() { return nextEntry != null; }
HashEntry<K,V> nextEntry() {
if (nextEntry == null)
throw new NoSuchElementException();
lastReturned = nextEntry;
advance();
return lastReturned;
}
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
ConcurrentHashMap.this.remove(lastReturned.key);
lastReturned = null;
}
}
final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
public K next() { return super.nextEntry().key; }
public K nextElement() { return super.nextEntry().key; }
}
final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
public V next() { return super.nextEntry().value; }
public V nextElement() { return super.nextEntry().value; }
}
/**
* Entry iterator. Exported Entry objects must write-through
* changes in setValue, even if the nodes have been cloned. So we
* cannot return internal HashEntry objects. Instead, the iterator
* itself acts as a forwarding pseudo-entry.
*/
final class EntryIterator extends HashIterator implements Map.Entry<K,V>, Iterator<Entry<K,V>> {
public Map.Entry<K,V> next() {
nextEntry();
return this;
}
public K getKey() {
if (lastReturned == null)
throw new IllegalStateException("Entry was removed");
return lastReturned.key;
}
public V getValue() {
if (lastReturned == null)
throw new IllegalStateException("Entry was removed");
return ConcurrentHashMap.this.get(lastReturned.key);
}
public V setValue(V value) {
if (lastReturned == null)
throw new IllegalStateException("Entry was removed");
return ConcurrentHashMap.this.put(lastReturned.key, value);
}
public boolean equals(Object o) {
// If not acting as entry, just use default.
if (lastReturned == null)
return super.equals(o);
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
return eq(getKey(), e.getKey()) && eq(getValue(), e.getValue());
}
public int hashCode() {
// If not acting as entry, just use default.
if (lastReturned == null)
return super.hashCode();
Object k = getKey();
Object v = getValue();
return ((k == null) ? 0 : k.hashCode()) ^
((v == null) ? 0 : v.hashCode());
}
public String toString() {
// If not acting as entry, just use default.
if (lastReturned == null)
return super.toString();
else
return getKey() + "=" + getValue();
}
boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
}
final class KeySet extends AbstractSet<K> {
public Iterator<K> iterator() {
return new KeyIterator();
}
public int size() {
return ConcurrentHashMap.this.size();
}
public boolean contains(Object o) {
return ConcurrentHashMap.this.containsKey(o);
}
public boolean remove(Object o) {
return ConcurrentHashMap.this.remove(o) != null;
}
public void clear() {
ConcurrentHashMap.this.clear();
}
}
final class Values extends AbstractCollection<V> {
public Iterator<V> iterator() {
return new ValueIterator();
}
public int size() {
return ConcurrentHashMap.this.size();
}
public boolean contains(Object o) {
return ConcurrentHashMap.this.containsValue(o);
}
public void clear() {
ConcurrentHashMap.this.clear();
}
}
final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
public Iterator<Map.Entry<K,V>> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<K,V> e = (Map.Entry<K,V>)o;
V v = ConcurrentHashMap.this.get(e.getKey());
return v != null && v.equals(e.getValue());
}
public boolean remove(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry<K,V> e = (Map.Entry<K,V>)o;
return ConcurrentHashMap.this.remove(e.getKey(), e.getValue());
}
public int size() {
return ConcurrentHashMap.this.size();
}
public void clear() {
ConcurrentHashMap.this.clear();
}
public Object[] toArray() {
// Since we don't ordinarily have distinct Entry objects, we
// must pack elements using exportable SimpleEntry
Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
c.add(new SimpleEntry<K,V>(i.next()));
return c.toArray();
}
public <T> T[] toArray(T[] a) {
Collection<Map.Entry<K,V>> c = new ArrayList<Map.Entry<K,V>>(size());
for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); )
c.add(new SimpleEntry<K,V>(i.next()));
return c.toArray(a);
}
}
/**
* This duplicates java.util.AbstractMap.SimpleEntry until this class
* is made accessible.
*/
static final class SimpleEntry<K,V> implements Entry<K,V> {
K key;
V value;
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Entry<K,V> e) {
this.key = e.getKey();
this.value = e.getValue();
}
public K getKey() {
return key;
}
public V getValue() {
return value;
}
public V setValue(V value) {
V 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;
}
static boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
}
/* ---------------- Serialization Support -------------- */
/**
* Save the state of the <tt>ConcurrentHashMap</tt>
* instance to a stream (i.e.,
* serialize it).
* @param s the stream
* @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 < segments.length; ++k) {
Segment<K,V> seg = (Segment<K,V>)segments[k];
seg.lock();
try {
HashEntry[] tab = seg.table;
for (int i = 0; i < tab.length; ++i) {
for (HashEntry<K,V> e = (HashEntry<K,V>)tab[i]; e != null; e = e.next) {
s.writeObject(e.key);
s.writeObject(e.value);
}
}
} finally {
seg.unlock();
}
}
s.writeObject(null);
s.writeObject(null);
}
/**
* Reconstitute the <tt>ConcurrentHashMap</tt>
* instance from a stream (i.e.,
* deserialize it).
* @param s the stream
*/
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 < segments.length; ++i) {
segments[i].setTable(new HashEntry[1]);
}
// Read the keys and values, and put the mappings in the table
for (;;) {
K key = (K) s.readObject();
V value = (V) s.readObject();
if (key == null)
break;
put(key, value);
}
}
}