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com.taobao.arthas.common.concurrent.ConcurrentWeakKeyHashMap Maven / Gradle / Ivy
/*
* Copyright 2012 The Netty Project
*
* The Netty Project 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 com.taobao.arthas.common.concurrent;
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.Arrays;
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.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantLock;
/**
* An alternative weak-key {@link ConcurrentMap} which is similar to
* {@link ConcurrentHashMap}.
* @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
*/
Segment segmentFor(int hash) {
return segments[hash >>> segmentShift & segmentMask];
}
private static 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 int keyHash() {
return hash;
}
public 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;
keyRef = new WeakKeyReference(key, hash, refQueue);
valueRef = value;
}
@SuppressWarnings("unchecked")
K key() {
return ((Reference) keyRef).get();
}
V value() {
return dereferenceValue(valueRef);
}
@SuppressWarnings("unchecked")
V dereferenceValue(Object value) {
if (value instanceof WeakKeyReference) {
return ((Reference) value).get();
}
return (V) value;
}
void setValue(V value) {
valueRef = value;
}
@SuppressWarnings("unchecked")
static 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 Segment[] newArray(int i) {
return new Segment[i];
}
private static 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
for (HashEntry e: table) {
for (; 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 (HashEntry e: oldTable) {
// We need to guarantee that any existing reads of old Map can
// proceed. So we cannot yet null out each bin.
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")
void removeStale() {
WeakKeyReference ref;
while ((ref = (WeakKeyReference) refQueue.poll()) != null) {
remove(ref.keyRef(), ref.keyHash(), null, true);
}
}
void clear() {
if (count != 0) {
lock();
try {
Arrays.fill(table, 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;
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 < segments.length; ++ i) {
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 (Segment segment: segments) {
segment.lock();
}
for (Segment segment: segments) {
sum += segment.count;
}
for (Segment segment: segments) {
segment.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 (Segment segment: segments) {
segment.lock();
}
boolean found = false;
try {
for (Segment segment: segments) {
if (segment.containsValue(value)) {
found = true;
break;
}
}
} finally {
for (Segment segment: segments) {
segment.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);
}
/**
* @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);
}
/**
* @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;
}
/**
* @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);
}
/**
* @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 (Segment segment: segments) {
segment.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 (Segment segment: segments) {
segment.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 nextEntry().key();
}
public K nextElement() {
return nextEntry().key();
}
}
final class ValueIterator
extends HashIterator implements ReusableIterator, Enumeration {
public V next() {
return nextEntry().value();
}
public V nextElement() {
return 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) {
key = entry.getKey();
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);
put(getKey(), value);
return v;
}
}
final class EntryIterator extends HashIterator implements
ReusableIterator> {
public Map.Entry next() {
HashEntry e = 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 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 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 = 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();
}
}
}
