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org.jboss.netty.util.internal.ConcurrentWeakKeyHashMap Maven / Gradle / Ivy
The Netty project is an effort to provide an asynchronous event-driven
network application framework and tools for rapid development of
maintainable high performance and high scalability protocol servers and
clients. In other words, Netty is a NIO client server framework which
enables quick and easy development of network applications such as protocol
servers and clients. It greatly simplifies and streamlines network
programming such as TCP and UDP socket server.
/*
* Copyright 2009 Red Hat, Inc.
*
* Red Hat 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.
*/
/*
* 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 org.jboss.netty.util.internal;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
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.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;
/**
* An alternative weak-key {@link ConcurrentMap} which is similar to
* {@link java.util.concurrent.ConcurrentHashMap}.
*
* @author The Netty Project
* @author Doug Lea
* @author Jason T. Greene
* @author Trustin Lee
* @version $Rev: 2371 $, $Date: 2010-10-19 15:00:42 +0900 (Tue, 19 Oct 2010) $
*
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
public final class ConcurrentWeakKeyHashMap extends AbstractMap implements ConcurrentMap {
/*
* The basic strategy is to subdivide the table among Segments,
* each of which itself is a concurrently readable hash table.
*/
/**
* 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 = 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 indexable using integers.
*/
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[] segments;
Set keySet;
Set> entrySet;
Collection values;
/* ---------------- Small Utilities -------------- */
/**
* Applies a supplemental hash function to a given hashCode, which defends
* against poor quality hash functions. This is critical because
* ConcurrentReferenceHashMap 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 segmentFor(int hash) {
return segments[hash >>> segmentShift & segmentMask];
}
private int hashOf(Object key) {
return hash(key.hashCode());
}
/* ---------------- Inner Classes -------------- */
/**
* A weak-key reference which stores the key hash needed for reclamation.
*/
static final class WeakKeyReference extends WeakReference {
final int hash;
WeakKeyReference(K key, int hash, ReferenceQueue refQueue) {
super(key, refQueue);
this.hash = hash;
}
public final int keyHash() {
return hash;
}
public final Object keyRef() {
return this;
}
}
/**
* ConcurrentReferenceHashMap 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 {
final Object keyRef;
final int hash;
volatile Object valueRef;
final HashEntry next;
HashEntry(
K key, int hash, HashEntry next, V value,
ReferenceQueue refQueue) {
this.hash = hash;
this.next = next;
this.keyRef = new WeakKeyReference(key, hash, refQueue);
this.valueRef = value;
}
@SuppressWarnings("unchecked")
final K key() {
return ((WeakReference) keyRef).get();
}
final V value() {
return dereferenceValue(valueRef);
}
@SuppressWarnings("unchecked")
final V dereferenceValue(Object value) {
if (value instanceof WeakKeyReference) {
return ((Reference) value).get();
}
return (V) value;
}
final void setValue(V value) {
this.valueRef = value;
}
@SuppressWarnings("unchecked")
static final HashEntry[] 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 extends ReentrantLock {
/*
* 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 = -8328104880676891126L;
/**
* 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.
*/
int modCount;
/**
* The table is rehashed when its size exceeds this threshold.
* (The value of this field is always (capacity * loadFactor) .)
*/
int threshold;
/**
* The per-segment table.
*/
transient volatile 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.
*/
final float loadFactor;
/**
* The collected weak-key reference queue for this segment. This should
* be (re)initialized whenever table is assigned,
*/
transient volatile ReferenceQueue refQueue;
Segment(int initialCapacity, float lf) {
loadFactor = lf;
setTable(HashEntry. newArray(initialCapacity));
}
@SuppressWarnings("unchecked")
static final Segment[] newArray(int i) {
return new Segment[i];
}
private boolean keyEq(Object src, Object dest) {
return src.equals(dest);
}
/**
* Sets table to new HashEntry array. Call only while holding lock or in
* constructor.
*/
void setTable(HashEntry[] newTable) {
threshold = (int) (newTable.length * loadFactor);
table = newTable;
refQueue = new ReferenceQueue();
}
/**
* Returns properly casted first entry of bin for given hash.
*/
HashEntry getFirst(int hash) {
HashEntry[] tab = table;
return tab[hash & tab.length - 1];
}
HashEntry newHashEntry(
K key, int hash, HashEntry next, V value) {
return new HashEntry(
key, hash, next, value, refQueue);
}
/**
* 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 e) {
lock();
try {
removeStale();
return e.value();
} finally {
unlock();
}
}
/* Specialized implementations of map methods */
V get(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && keyEq(key, e.key())) {
Object opaque = e.valueRef;
if (opaque != null) {
return e.dereferenceValue(opaque);
}
return readValueUnderLock(e); // recheck
}
e = e.next;
}
}
return null;
}
boolean containsKey(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && keyEq(key, 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 e = tab[i]; e != null; e = e.next) {
Object opaque = e.valueRef;
V v;
if (opaque == null) {
v = readValueUnderLock(e); // recheck
} else {
v = e.dereferenceValue(opaque);
}
if (value.equals(v)) {
return true;
}
}
}
}
return false;
}
boolean replace(K key, int hash, V oldValue, V newValue) {
lock();
try {
removeStale();
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
boolean replaced = false;
if (e != null && oldValue.equals(e.value())) {
replaced = true;
e.setValue(newValue);
}
return replaced;
} finally {
unlock();
}
}
V replace(K key, int hash, V newValue) {
lock();
try {
removeStale();
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
V oldValue = null;
if (e != null) {
oldValue = e.value();
e.setValue(newValue);
}
return oldValue;
} finally {
unlock();
}
}
V put(K key, int hash, V value, boolean onlyIfAbsent) {
lock();
try {
removeStale();
int c = count;
if (c ++ > threshold) { // ensure capacity
int reduced = rehash();
if (reduced > 0) {
count = (c -= reduced) - 1; // write-volatile
}
}
HashEntry[] tab = table;
int index = hash & tab.length - 1;
HashEntry first = tab[index];
HashEntry e = first;
while (e != null && (e.hash != hash || !keyEq(key, e.key()))) {
e = e.next;
}
V oldValue;
if (e != null) {
oldValue = e.value();
if (!onlyIfAbsent) {
e.setValue(value);
}
} else {
oldValue = null;
++ modCount;
tab[index] = newHashEntry(key, hash, first, value);
count = c; // write-volatile
}
return oldValue;
} finally {
unlock();
}
}
int rehash() {
HashEntry[] oldTable = table;
int oldCapacity = oldTable.length;
if (oldCapacity >= MAXIMUM_CAPACITY) {
return 0;
}
/*
* 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 = HashEntry.newArray(oldCapacity << 1);
threshold = (int) (newTable.length * loadFactor);
int sizeMask = newTable.length - 1;
int reduce = 0;
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 e = oldTable[i];
if (e != null) {
HashEntry 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 lastRun = e;
int lastIdx = idx;
for (HashEntry 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 p = e; p != lastRun; p = p.next) {
// Skip GC'd weak references
K key = p.key();
if (key == null) {
reduce ++;
continue;
}
int k = p.hash & sizeMask;
HashEntry n = newTable[k];
newTable[k] = newHashEntry(key, p.hash, n, p.value());
}
}
}
}
table = newTable;
return reduce;
}
/**
* Remove; match on key only if value null, else match both.
*/
V remove(Object key, int hash, Object value, boolean refRemove) {
lock();
try {
if (!refRemove) {
removeStale();
}
int c = count - 1;
HashEntry[] tab = table;
int index = hash & tab.length - 1;
HashEntry first = tab[index];
HashEntry e = first;
// a reference remove operation compares the Reference instance
while (e != null && key != e.keyRef &&
(refRemove || hash != e.hash || !keyEq(key, 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 newFirst = e.next;
for (HashEntry p = first; p != e; p = p.next) {
K pKey = p.key();
if (pKey == null) { // Skip GC'd keys
c --;
continue;
}
newFirst = newHashEntry(
pKey, p.hash, newFirst, p.value());
}
tab[index] = newFirst;
count = c; // write-volatile
}
}
return oldValue;
} finally {
unlock();
}
}
@SuppressWarnings("rawtypes")
final void removeStale() {
WeakKeyReference ref;
while ((ref = (WeakKeyReference) refQueue.poll()) != null) {
remove(ref.keyRef(), ref.keyHash(), null, true);
}
}
void clear() {
if (count != 0) {
lock();
try {
HashEntry[] tab = table;
for (int i = 0; i < tab.length; i ++) {
tab[i] = null;
}
++ modCount;
// replace the reference queue to avoid unnecessary stale
// cleanups
refQueue = new ReferenceQueue();
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 ConcurrentWeakKeyHashMap(
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;
}
int cap = 1;
while (cap < c) {
cap <<= 1;
}
for (int i = 0; i < this.segments.length; ++ i) {
this.segments[i] = new Segment(cap, loadFactor);
}
}
/**
* Creates a new, empty map with the specified initial capacity and load
* factor and with the default reference types (weak keys, strong values),
* and 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
*/
public ConcurrentWeakKeyHashMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the specified initial capacity, and with
* default reference types (weak keys, strong values), 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 ConcurrentWeakKeyHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with a default initial capacity (16), reference
* types (weak keys, strong values), default load factor (0.75) and
* concurrencyLevel (16).
*/
public ConcurrentWeakKeyHashMap() {
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 ConcurrentWeakKeyHashMap(Map m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL);
putAll(m);
}
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings
*/
@Override
public boolean isEmpty() {
final Segment[] 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 Integer.MAX_VALUE elements, returns
* Integer.MAX_VALUE .
*
* @return the number of key-value mappings in this map
*/
@Override
public int size() {
final Segment[] 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.
*
* 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
*/
@Override
public V get(Object key) {
int hash = hashOf(key);
return segmentFor(hash).get(key, hash);
}
/**
* Tests if the specified object is a key in this table.
*
* @param key possible key
* @return true if and only if the specified object is a key in
* this table, as determined by the equals method;
* false otherwise.
* @throws NullPointerException if the specified key is null
*/
@Override
public boolean containsKey(Object key) {
int hash = hashOf(key);
return segmentFor(hash).containsKey(key, hash);
}
/**
* Returns true 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 containsKey .
*
* @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
* @throws NullPointerException if the specified value is null
*/
@Override
public boolean containsValue(Object value) {
if (value == null) {
throw new NullPointerException();
}
// See explanation of modCount use above
final Segment[] 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 mcsum = 0;
for (int i = 0; i < segments.length; ++ i) {
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) {
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 Hashtable}, which supported this method prior to
* introduction of the Java Collections framework.
*
* @param value a value to search for
* @return true if and only if some key maps to the value
* argument in this table as determined by the equals
* method; false 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.
*
* The value can be retrieved by calling the get 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 key , or null
* if there was no mapping for key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V put(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
int hash = hashOf(key);
return segmentFor(hash).put(key, hash, value, false);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or
* null 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 = hashOf(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 m mappings to be stored in this map
*/
@Override
public void putAll(Map m) {
for (Map.Entry 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 key , or null
* if there was no mapping for key
* @throws NullPointerException if the specified key is null
*/
@Override
public V remove(Object key) {
int hash = hashOf(key);
return segmentFor(hash).remove(key, hash, null, false);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if the specified key is null
*/
public boolean remove(Object key, Object value) {
int hash = hashOf(key);
if (value == null) {
return false;
}
return segmentFor(hash).remove(key, hash, value, false) != 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 = hashOf(key);
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key, or
* null 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 = hashOf(key);
return segmentFor(hash).replace(key, hash, value);
}
/**
* Removes all of the mappings from this map.
*/
@Override
public void clear() {
for (int i = 0; i < segments.length; ++ i) {
segments[i].clear();
}
}
/**
* Removes any stale entries whose keys have been finalized. Use of this
* method is normally not necessary since stale entries are automatically
* removed lazily, when blocking operations are required. However, there are
* some cases where this operation should be performed eagerly, such as
* cleaning up old references to a ClassLoader in a multi-classloader
* environment.
*
* Note: this method will acquire locks, one at a time, across all segments
* of this table, so if it is to be used, it should be used sparingly.
*/
public void purgeStaleEntries() {
for (int i = 0; i < segments.length; ++ i) {
segments[i].removeStale();
}
}
/**
* 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 Iterator.remove ,
* Set.remove , removeAll , retainAll , and
* clear operations. It does not support the add or
* addAll operations.
*
*
The view's iterator 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.
*/
@Override
public Set keySet() {
Set 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
* Iterator.remove , Collection.remove , removeAll ,
* retainAll , and clear operations. It does not support
* the add or addAll operations.
*
* The view's iterator 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.
*/
@Override
public Collection values() {
Collection 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 Iterator.remove ,
* Set.remove , removeAll , retainAll , and
* clear operations. It does not support the add or
* addAll operations.
*
* The view's iterator 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.
*/
@Override
public Set> entrySet() {
Set> 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 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 elements() {
return new ValueIterator();
}
/* ---------------- Iterator Support -------------- */
abstract class HashIterator {
int nextSegmentIndex;
int nextTableIndex;
HashEntry[] currentTable;
HashEntry nextEntry;
HashEntry lastReturned;
K currentKey; // Strong reference to weak key (prevents gc)
HashIterator() {
nextSegmentIndex = segments.length - 1;
nextTableIndex = -1;
advance();
}
public void rewind() {
nextSegmentIndex = segments.length - 1;
nextTableIndex = -1;
currentTable = null;
nextEntry = null;
lastReturned = null;
currentKey = null;
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 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() {
while (nextEntry != null) {
if (nextEntry.key() != null) {
return true;
}
advance();
}
return false;
}
HashEntry nextEntry() {
do {
if (nextEntry == null) {
throw new NoSuchElementException();
}
lastReturned = nextEntry;
currentKey = lastReturned.key();
advance();
} while (currentKey == null); // Skip GC'd keys
return lastReturned;
}
public void remove() {
if (lastReturned == null) {
throw new IllegalStateException();
}
ConcurrentWeakKeyHashMap.this.remove(currentKey);
lastReturned = null;
}
}
final class KeyIterator
extends HashIterator implements ReusableIterator, Enumeration {
public K next() {
return super.nextEntry().key();
}
public K nextElement() {
return super.nextEntry().key();
}
}
final class ValueIterator
extends HashIterator implements ReusableIterator, Enumeration {
public V next() {
return super.nextEntry().value();
}
public V nextElement() {
return super.nextEntry().value();
}
}
/*
* This class is needed for JDK5 compatibility.
*/
static class SimpleEntry implements Entry {
private final K key;
private V value;
public SimpleEntry(K key, V value) {
this.key = key;
this.value = value;
}
public SimpleEntry(Entry entry) {
this.key = entry.getKey();
this.value = entry.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;
}
@Override
public boolean equals(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
@SuppressWarnings("rawtypes")
Map.Entry e = (Map.Entry) o;
return eq(key, e.getKey()) && eq(value, e.getValue());
}
@Override
public int hashCode() {
return (key == null? 0 : key.hashCode()) ^ (value == null? 0 : value.hashCode());
}
@Override
public String toString() {
return key + "=" + value;
}
private static boolean eq(Object o1, Object o2) {
return o1 == null? o2 == null : o1.equals(o2);
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays setValue
* changes to the underlying map.
*/
final class WriteThroughEntry extends SimpleEntry {
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 can
* not guarantee more.
*/
@Override
public V setValue(V value) {
if (value == null) {
throw new NullPointerException();
}
V v = super.setValue(value);
ConcurrentWeakKeyHashMap.this.put(getKey(), value);
return v;
}
}
final class EntryIterator extends HashIterator implements
ReusableIterator> {
public Map.Entry next() {
HashEntry e = super.nextEntry();
return new WriteThroughEntry(e.key(), e.value());
}
}
final class KeySet extends AbstractSet {
@Override
public Iterator iterator() {
return new KeyIterator();
}
@Override
public int size() {
return ConcurrentWeakKeyHashMap.this.size();
}
@Override
public boolean isEmpty() {
return ConcurrentWeakKeyHashMap.this.isEmpty();
}
@Override
public boolean contains(Object o) {
return ConcurrentWeakKeyHashMap.this.containsKey(o);
}
@Override
public boolean remove(Object o) {
return ConcurrentWeakKeyHashMap.this.remove(o) != null;
}
@Override
public void clear() {
ConcurrentWeakKeyHashMap.this.clear();
}
}
final class Values extends AbstractCollection {
@Override
public Iterator iterator() {
return new ValueIterator();
}
@Override
public int size() {
return ConcurrentWeakKeyHashMap.this.size();
}
@Override
public boolean isEmpty() {
return ConcurrentWeakKeyHashMap.this.isEmpty();
}
@Override
public boolean contains(Object o) {
return ConcurrentWeakKeyHashMap.this.containsValue(o);
}
@Override
public void clear() {
ConcurrentWeakKeyHashMap.this.clear();
}
}
final class EntrySet extends AbstractSet> {
@Override
public Iterator> iterator() {
return new EntryIterator();
}
@Override
public boolean contains(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry) o;
V v = ConcurrentWeakKeyHashMap.this.get(e.getKey());
return v != null && v.equals(e.getValue());
}
@Override
public boolean remove(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry) o;
return ConcurrentWeakKeyHashMap.this.remove(e.getKey(), e.getValue());
}
@Override
public int size() {
return ConcurrentWeakKeyHashMap.this.size();
}
@Override
public boolean isEmpty() {
return ConcurrentWeakKeyHashMap.this.isEmpty();
}
@Override
public void clear() {
ConcurrentWeakKeyHashMap.this.clear();
}
}
}
