/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code 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 General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* 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 hashtables.lockbased;
import java.io.IOException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantLock;
import contention.abstractions.CompositionalMap;
import contention.abstractions.CompositionalMap.Vars;
/**
* 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 <tt>16</tt>), which
* is used as a hint for internal sizing. The table is internally partitioned to
* try to permit the indicated number of concurrent updates without contention.
* Because placement in hash tables is essentially random, the actual
* concurrency will vary. Ideally, you should choose a value to accommodate as
* many threads as will ever concurrently modify the table. Using a
* significantly higher value than you need can waste space and time, and a
* significantly lower value can lead to thread contention. But overestimates
* and underestimates within an order of magnitude do not usually have much
* noticeable impact. A value of one is appropriate when it is known that only
* one thread will modify and all others will only read. Also, resizing this or
* any other kind of hash table is a relatively slow operation, so, when
* possible, it is a good idea to provide estimates of expected table sizes in
* constructors.
*
* <p>
* This class and its views and iterators implement all of the <em>optional</em>
* methods of the {@link Map} and {@link Iterator} interfaces.
*
* <p>
* Like {@link Hashtable} but unlike {@link HashMap}, this class does
* <em>not</em> allow <tt>null</tt> to be used as a key or value.
*
* <p>
* This class is a member of the <a href="{@docRoot}
* /../technotes/guides/collections/index.html"> Java Collections Framework</a>.
*
* @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 LockBasedJavaHashMap<K, V> extends AbstractMap<K, V> implements
ConcurrentMap<K, V>, CompositionalMap<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 capacity for this table, used when not otherwise
* specified in a constructor.
*/
static final int DEFAULT_INITIAL_CAPACITY = 16;
/**
* The default load factor for this table, used when not otherwise specified
* in a constructor.
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The default concurrency level for this table, used when not otherwise
* specified in a constructor.
*/
static final int DEFAULT_CONCURRENCY_LEVEL = 64;
/**
* The maximum capacity, used if a higher value is implicitly specified by
* either of the constructors with arguments. MUST be a power of two <=
* 1<<30 to ensure that entries are indexable using ints.
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* The maximum number of segments to allow; used to bound constructor
* arguments.
*/
static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
/**
* Number of unsynchronized retries in size and containsValue methods before
* resorting to locking. This is used to avoid unbounded retries if tables
* undergo continuous modification which would make it impossible to obtain
* an accurate result.
*/
static final int RETRIES_BEFORE_LOCK = 2;
/* ---------------- Fields -------------- */
/**
* Mask value for indexing into segments. The upper bits of a key's hash
* code are used to choose the segment.
*/
final int segmentMask;
/**
* Shift value for indexing within segments.
*/
final int segmentShift;
/**
* The segments, each of which is a specialized hash table
*/
final Segment<K, V>[] segments;
transient Set<K> keySet;
transient Set<Map.Entry<K, V>> entrySet;
transient Collection<V> values;
private int cap;
private float loadFactor;
/* ---------------- Small Utilities -------------- */
/**
* Applies a supplemental hash function to a given hashCode, which defends
* against poor quality hash functions. This is critical because
* ConcurrentHashMap uses power-of-two length hash tables, that otherwise
* encounter collisions for hashCodes that do not differ in lower or upper
* bits.
*/
private static int hash(int h) {
// Spread bits to regularize both segment and index locations,
// using variant of single-word Wang/Jenkins hash.
h += (h << 15) ^ 0xffffcd7d;
h ^= (h >>> 10);
h += (h << 3);
h ^= (h >>> 6);
h += (h << 2) + (h << 14);
return h ^ (h >>> 16);
}
/**
* 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 segments[(hash >>> segmentShift) & segmentMask];
}
/* ---------------- Inner Classes -------------- */
/**
* ConcurrentHashMap list entry. Note that this is never exported out as a
* user-visible Map.Entry.
*
* Because the value field is volatile, not final, it is legal wrt the Java
* Memory Model for an unsynchronized reader to see null instead of initial
* value when read via a data race. Although a reordering leading to this is
* not likely to ever actually occur, the Segment.readValueUnderLock method
* is used as a backup in case a null (pre-initialized) value is ever seen
* in an unsynchronized access method.
*/
static final class HashEntry<K, V> {
final K key;
final int hash;
volatile V value;
final HashEntry<K, V> next;
HashEntry(K key, int hash, HashEntry<K, V> next, V value) {
this.key = key;
this.hash = hash;
this.next = next;
this.value = value;
}
@SuppressWarnings("unchecked")
static final <K, V> HashEntry<K, V>[] newArray(int i) {
return new HashEntry[i];
}
}
/**
* 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
* selected uses of volatiles to ensure that completed write operations
* performed by other threads are noticed. For most purposes, the
* "count" field, tracking the number of elements, serves as that
* volatile variable ensuring visibility. This is convenient because
* this field needs to be read in many read operations anyway:
*
* - All (unsynchronized) read operations must first read the "count"
* field, and should not look at table entries if it is 0.
*
* - All (synchronized) write operations should write to the "count"
* field after structurally changing any bin. The operations must not
* take any action that could even momentarily cause a concurrent read
* operation to see inconsistent data. This is made easier by the nature
* of the read operations in Map. For example, no operation can reveal
* that the table has grown but the threshold has not yet been updated,
* so there are no atomicity requirements for this with respect to
* reads.
*
* As a guide, all critical volatile reads and writes to the count field
* are marked in code comments.
*/
private static final long serialVersionUID = 2249069246763182397L;
/**
* The number of elements in this segment's region.
*/
transient volatile int count;
/**
* Number of updates that alter the size of the table. This is used
* during bulk-read methods to make sure they see a consistent snapshot:
* If modCounts change during a traversal of segments computing size or
* checking containsValue, then we might have an inconsistent view of
* state so (usually) must retry.
*/
transient int modCount;
/**
* The table is rehashed when its size exceeds this threshold. (The
* value of this field is always <tt>(int)(capacity *
* loadFactor)</tt>.)
*/
transient int threshold;
/**
* The per-segment table.
*/
transient volatile HashEntry<K, V>[] table;
/**
* The load factor for the hash table. Even though this value is same
* for all segments, it is replicated to avoid needing links to outer
* object.
*
* @serial
*/
final float loadFactor;
Segment(int initialCapacity, float lf) {
loadFactor = lf;
setTable(HashEntry.<K, V> newArray(initialCapacity));
}
@SuppressWarnings("unchecked")
static final <K, V> Segment<K, V>[] newArray(int i) {
return new Segment[i];
}
/**
* Sets table to new HashEntry array. Call only while holding lock or in
* constructor.
*/
void setTable(HashEntry<K, V>[] newTable) {
threshold = (int) (newTable.length * loadFactor);
table = newTable;
}
/**
* Returns properly casted first entry of bin for given hash.
*/
HashEntry<K, V> getFirst(int hash) {
HashEntry<K, V>[] tab = table;
return tab[hash & (tab.length - 1)];
}
/**
* Reads value field of an entry under lock. Called if value field ever
* appears to be null. This is possible only if a compiler happens to
* reorder a HashEntry initialization with its table assignment, which
* is legal under memory model but is not known to ever occur.
*/
V readValueUnderLock(HashEntry<K, V> e) {
System.out.println("in read under lock");
lock();
try {
return e.value;
} finally {
unlock();
}
}
/* Specialized implementations of map methods */
void finishCount(int nodesTraversed) {
Vars vars = counts.get();
vars.getCount++;
vars.nodesTraversed += nodesTraversed;
}
V get(Object key, int hash) {
int nodesTraversed = 0;
if (count != 0) { // read-volatile
HashEntry<K, V> e = getFirst(hash);
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
while (e != null) {
if (e.hash == hash && key.equals(e.key)) {
V v = e.value;
if (TRAVERSAL_COUNT) {
finishCount(nodesTraversed);
}
if (v != null)
return v;
return readValueUnderLock(e); // recheck
}
e = e.next;
if (TRAVERSAL_COUNT) {
nodesTraversed++;
}
}
}
if (TRAVERSAL_COUNT) {
finishCount(nodesTraversed);
}
return null;
}
boolean containsKey(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry<K, V> e = getFirst(hash);
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<K, V>[] tab = table;
int len = tab.length;
for (int i = 0; i < len; i++) {
for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
V v = e.value;
if (v == null) // recheck
v = readValueUnderLock(e);
if (value.equals(v))
return true;
}
}
}
return false;
}
boolean replace(K key, int hash, V oldValue, V newValue) {
lock();
try {
HashEntry<K, V> e = getFirst(hash);
while (e != null && (e.hash != hash || !key.equals(e.key)))
e = e.next;
boolean replaced = false;
if (e != null && oldValue.equals(e.value)) {
replaced = true;
e.value = newValue;
}
return replaced;
} finally {
unlock();
}
}
V replace(K key, int hash, V newValue) {
lock();
try {
HashEntry<K, V> e = getFirst(hash);
while (e != null && (e.hash != hash || !key.equals(e.key)))
e = e.next;
V oldValue = null;
if (e != null) {
oldValue = e.value;
e.value = newValue;
}
return oldValue;
} finally {
unlock();
}
}
V put(K key, int hash, V value, boolean onlyIfAbsent) {
lock();
try {
int c = count;
if (c++ > threshold) // ensure capacity
rehash();
HashEntry<K, V>[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K, V> first = tab[index];
HashEntry<K, V> e = first;
while (e != null && (e.hash != hash || !key.equals(e.key)))
e = e.next;
V oldValue;
if (e != null) {
oldValue = e.value;
if (!onlyIfAbsent)
e.value = value;
} else {
oldValue = null;
++modCount;
tab[index] = new HashEntry<K, V>(key, hash, first, value);
count = c; // write-volatile
}
return oldValue;
} finally {
unlock();
}
}
void rehash() {
HashEntry<K, V>[] oldTable = table;
int oldCapacity = oldTable.length;
if (oldCapacity >= MAXIMUM_CAPACITY)
return;
/*
* 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.
*/
// System.out.println("rehash");
if (STRUCT_MODS)
counts.get().structMods += 1;
HashEntry<K, V>[] newTable = HashEntry.newArray(oldCapacity << 1);
threshold = (int) (newTable.length * loadFactor);
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 = 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;
HashEntry<K, V> n = newTable[k];
newTable[k] = new HashEntry<K, V>(p.key, p.hash, n,
p.value);
}
}
}
}
table = 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 - 1;
HashEntry<K, V>[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<K, V> first = tab[index];
HashEntry<K, V> e = first;
while (e != null && (e.hash != hash || !key.equals(e.key)))
e = e.next;
V oldValue = null;
if (e != null) {
V v = e.value;
if (value == null || value.equals(v)) {
oldValue = v;
// All entries following removed node can stay
// in list, but all preceding ones need to be
// cloned.
++modCount;
HashEntry<K, V> newFirst = e.next;
for (HashEntry<K, V> p = first; p != e; p = p.next)
newFirst = new HashEntry<K, V>(p.key, p.hash,
newFirst, p.value);
tab[index] = newFirst;
count = c; // write-volatile
}
}
return oldValue;
} finally {
unlock();
}
}
void clear() {
if (count != 0) {
lock();
try {
HashEntry<K, V>[] tab = table;
for (int i = 0; i < tab.length; i++)
tab[i] = null;
++modCount;
count = 0; // write-volatile
} finally {
unlock();
}
}
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the specified initial capacity, load factor
* and concurrency level.
*
* @param initialCapacity
* the initial capacity. The implementation performs internal
* sizing to accommodate this many elements.
* @param loadFactor
* the load factor threshold, used to control resizing. Resizing
* may be performed when the average number of elements per bin
* exceeds this threshold.
* @param concurrencyLevel
* the estimated number of concurrently updating threads. The
* implementation performs internal sizing to try to accommodate
* this many threads.
* @throws IllegalArgumentException
* if the initial capacity is negative or the load factor or
* concurrencyLevel are nonpositive.
*/
public LockBasedJavaHashMap(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 = Segment.newArray(ssize);
if (initialCapacity > MAXIMUM_CAPACITY)
initialCapacity = MAXIMUM_CAPACITY;
int c = initialCapacity / ssize;
if (c * ssize < initialCapacity)
++c;
this.cap = 1;
while (cap < c)
cap <<= 1;
this.loadFactor = loadFactor;
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 load
* factor and with the default concurrencyLevel (16).
*
* @param initialCapacity
* The implementation performs internal sizing to accommodate
* this many elements.
* @param loadFactor
* the load factor threshold, used to control resizing. Resizing
* may be performed when the average number of elements per bin
* exceeds this threshold.
* @throws IllegalArgumentException
* if the initial capacity of elements is negative or the load
* factor is nonpositive
*
* @since 1.6
*/
public LockBasedJavaHashMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the specified initial capacity, and with
* default load factor (0.75) and concurrencyLevel (16).
*
* @param initialCapacity
* the initial capacity. The implementation performs internal
* sizing to accommodate this many elements.
* @throws IllegalArgumentException
* if the initial capacity of elements is negative.
*/
public LockBasedJavaHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with a default initial capacity (16), load
* factor (0.75) and concurrencyLevel (16).
*/
public LockBasedJavaHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new map with the same mappings as the given map. The map is
* created with a capacity of 1.5 times the number of mappings in the given
* map or 16 (whichever is greater), and a default load factor (0.75) and
* concurrencyLevel (16).
*
* @param m
* the map
*/
public LockBasedJavaHashMap(Map<? extends K, ? extends V> m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL);
putAll(m);
}
/**
* Returns <tt>true</tt> if this map contains no key-value mappings.
*
* @return <tt>true</tt> if this map contains no key-value mappings
*/
public boolean isEmpty() {
final Segment<K, V>[] segments = this.segments;
/*
* We keep track of per-segment modCounts to avoid ABA problems in which
* an element in one segment was added and in another removed during
* traversal, in which case the table was never actually empty at any
* point. Note the similar use of modCounts in the size() and
* containsValue() methods, which are the only other methods also
* susceptible to ABA problems.
*/
int[] mc = new int[segments.length];
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
if (segments[i].count != 0)
return false;
else
mcsum += mc[i] = segments[i].modCount;
}
// If mcsum happens to be zero, then we know we got a snapshot
// before any modifications at all were made. This is
// probably common enough to bother tracking.
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
if (segments[i].count != 0 || mc[i] != segments[i].modCount)
return false;
}
}
return true;
}
/**
* Returns the number of key-value mappings in this map. If the map contains
* more than <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.
*
* @return the number of key-value mappings in this map
*/
public int size() {
final Segment<K, V>[] segments = this.segments;
long sum = 0;
long check = 0;
int[] mc = new int[segments.length];
// Try a few times to get accurate count. On failure due to
// continuous async changes in table, resort to locking.
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
check = 0;
sum = 0;
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
sum += segments[i].count;
mcsum += mc[i] = segments[i].modCount;
}
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
check += segments[i].count;
if (mc[i] != segments[i].modCount) {
check = -1; // force retry
break;
}
}
}
if (check == sum)
break;
}
if (check != sum) { // Resort to locking all segments
sum = 0;
for (int i = 0; i < segments.length; ++i)
segments[i].lock();
for (int i = 0; i < segments.length; ++i)
sum += segments[i].count;
for (int i = 0; i < segments.length; ++i)
segments[i].unlock();
}
if (sum > Integer.MAX_VALUE)
return Integer.MAX_VALUE;
else
return (int) sum;
}
/**
* Returns the value to which the specified key is mapped, or {@code null}
* if this map contains no mapping for the key.
*
* <p>
* More formally, if this map contains a mapping from a key {@code k} to a
* value {@code v} such that {@code key.equals(k)}, then this method returns
* {@code v}; otherwise it returns {@code null}. (There can be at most one
* such mapping.)
*
* @throws NullPointerException
* if the specified key is null
*/
public V get(Object key) {
int hash = hash(key.hashCode());
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 specified key is null
*/
public boolean containsKey(Object key) {
int hash = hash(key.hashCode());
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 specified value is null
*/
public boolean containsValue(Object value) {
if (value == null)
throw new NullPointerException();
// See explanation of modCount use above
final Segment<K, V>[] segments = this.segments;
int[] mc = new int[segments.length];
// Try a few times without locking
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
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;
}
// Resort to locking all segments
for (int i = 0; i < segments.length; ++i)
segments[i].lock();
boolean found = false;
try {
for (int i = 0; i < segments.length; ++i) {
if (segments[i].containsValue(value)) {
found = true;
break;
}
}
} finally {
for (int i = 0; i < segments.length; ++i)
segments[i].unlock();
}
return found;
}
/**
* 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 specified value is null
*/
public boolean contains(Object value) {
return containsValue(value);
}
/**
* Maps the specified key to the specified value in this table. Neither the
* key nor the value can be null.
*
* <p>
* The value can be retrieved by calling the <tt>get</tt> method with a key
* that is equal to the original key.
*
* @param key
* key with which the specified value is to be associated
* @param value
* value to be associated with the specified key
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt>
* if there was no mapping for <tt>key</tt>
* @throws NullPointerException
* if the specified key or value is null
*/
public V put(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key.hashCode());
return segmentFor(hash).put(key, hash, value, false);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or
* <tt>null</tt> if there was no mapping for the key
* @throws NullPointerException
* if the specified key or value is null
*/
public V putIfAbsent(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key.hashCode());
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 m
* mappings to be stored in this map
*/
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
}
/**
* Removes the key (and its corresponding value) from this map. This method
* does nothing if the key is not in the map.
*
* @param key
* the key that needs to be removed
* @return the previous value associated with <tt>key</tt>, or <tt>null</tt>
* if there was no mapping for <tt>key</tt>
* @throws NullPointerException
* if the specified key is null
*/
public V remove(Object key) {
int hash = hash(key.hashCode());
return segmentFor(hash).remove(key, hash, null);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException
* if the specified key is null
*/
public boolean remove(Object key, Object value) {
int hash = hash(key.hashCode());
if (value == null)
return false;
return segmentFor(hash).remove(key, hash, value) != null;
}
/**
* {@inheritDoc}
*
* @throws NullPointerException
* if any of the arguments are null
*/
public boolean replace(K key, V oldValue, V newValue) {
if (oldValue == null || newValue == null)
throw new NullPointerException();
int hash = hash(key.hashCode());
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or
* <tt>null</tt> if there was no mapping for the key
* @throws NullPointerException
* if the specified key or value is null
*/
public V replace(K key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key.hashCode());
return segmentFor(hash).replace(key, hash, value);
}
/**
* Removes all of the mappings from this map.
*/
public void clear() {
for (int i = 0; i < segments.length; ++i)
// segments[i].clear();
// want a real clear
this.segments[i] = new Segment<K, V>(cap, loadFactor);
}
/**
* Returns a {@link Set} view of the keys contained in this map. The set is
* backed by the map, so changes to the map are reflected in the set, and
* vice-versa. The set supports element removal, which removes the
* corresponding mapping from this map, via the <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.
*
* <p>
* The view's <tt>iterator</tt> is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*/
public Set<K> keySet() {
Set<K> ks = keySet;
return (ks != null) ? ks : (keySet = new KeySet());
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are reflected
* in the collection, and vice-versa. The collection supports element
* removal, which removes the corresponding mapping from this map, via the
* <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.
*
* <p>
* The view's <tt>iterator</tt> is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*/
public Collection<V> values() {
Collection<V> vs = values;
return (vs != null) ? vs : (values = new Values());
}
/**
* Returns a {@link Set} view of the mappings contained in this map. The set
* is backed by the map, so changes to the map are reflected in the set, and
* vice-versa. The set supports element removal, which removes the
* corresponding mapping from the map, via the <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.
*
* <p>
* The view's <tt>iterator</tt> is a "weakly consistent" iterator that will
* never throw {@link ConcurrentModificationException}, and guarantees to
* traverse elements as they existed upon construction of the iterator, and
* may (but is not guaranteed to) reflect any modifications subsequent to
* construction.
*/
public Set<Map.Entry<K, V>> entrySet() {
Set<Map.Entry<K, V>> es = entrySet;
return (es != null) ? es : (entrySet = 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<K, V>[] 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 = currentTable[nextTableIndex--]) != null)
return;
}
while (nextSegmentIndex >= 0) {
Segment<K, V> seg = segments[nextSegmentIndex--];
if (seg.count != 0) {
currentTable = seg.table;
for (int j = currentTable.length - 1; j >= 0; --j) {
if ((nextEntry = 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();
LockBasedJavaHashMap.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;
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays setValue
* changes to the underlying map.
*/
final class WriteThroughEntry extends AbstractMap.SimpleEntry<K, V> {
WriteThroughEntry(K k, V v) {
super(k, v);
}
/**
* Set our entry's value and write through to the map. The value to
* return is somewhat arbitrary here. Since a WriteThroughEntry does not
* necessarily track asynchronous changes, the most recent "previous"
* value could be different from what we return (or could even have been
* removed in which case the put will re-establish). We do not and
* cannot guarantee more.
*/
public V setValue(V value) {
if (value == null)
throw new NullPointerException();
V v = super.setValue(value);
LockBasedJavaHashMap.this.put(getKey(), value);
return v;
}
}
final class EntryIterator extends HashIterator implements
Iterator<Entry<K, V>> {
public Map.Entry<K, V> next() {
HashEntry<K, V> e = super.nextEntry();
return new WriteThroughEntry(e.key, e.value);
}
}
final class KeySet extends AbstractSet<K> {
public Iterator<K> iterator() {
return new KeyIterator();
}
public int size() {
return LockBasedJavaHashMap.this.size();
}
public boolean isEmpty() {
return LockBasedJavaHashMap.this.isEmpty();
}
public boolean contains(Object o) {
return LockBasedJavaHashMap.this.containsKey(o);
}
public boolean remove(Object o) {
return LockBasedJavaHashMap.this.remove(o) != null;
}
public void clear() {
LockBasedJavaHashMap.this.clear();
}
}
final class Values extends AbstractCollection<V> {
public Iterator<V> iterator() {
return new ValueIterator();
}
public int size() {
return LockBasedJavaHashMap.this.size();
}
public boolean isEmpty() {
return LockBasedJavaHashMap.this.isEmpty();
}
public boolean contains(Object o) {
return LockBasedJavaHashMap.this.containsValue(o);
}
public void clear() {
LockBasedJavaHashMap.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<?, ?> e = (Map.Entry<?, ?>) o;
V v = LockBasedJavaHashMap.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<?, ?> e = (Map.Entry<?, ?>) o;
return LockBasedJavaHashMap.this.remove(e.getKey(), e.getValue());
}
public int size() {
return LockBasedJavaHashMap.this.size();
}
public boolean isEmpty() {
return LockBasedJavaHashMap.this.isEmpty();
}
public void clear() {
LockBasedJavaHashMap.this.clear();
}
}
/* ---------------- 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 = segments[k];
seg.lock();
try {
HashEntry<K, V>[] tab = seg.table;
for (int i = 0; i < tab.length; ++i) {
for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
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);
}
}
}