/*
* Copyright (c) 2008-2013, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.util;
/*
* 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
*/
import java.io.
IOException;
import java.io.
Serializable;
import java.lang.ref.
Reference;
import java.lang.ref.
ReferenceQueue;
import java.lang.ref.
SoftReference;
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.
EnumSet;
import java.util.
Enumeration;
import java.util.
HashMap;
import java.util.
Hashtable;
import java.util.
IdentityHashMap;
import java.util.
Iterator;
import java.util.
Map;
import java.util.
NoSuchElementException;
import java.util.
Set;
import java.util.concurrent.locks.
ReentrantLock;
/**
* An advanced hash table supporting configurable garbage collection semantics
* of keys and values, optional referential-equality, full concurrency of
* retrievals, and adjustable expected concurrency for updates.
*
* This table is designed around specific advanced use-cases. If there is any
* doubt whether this table is for you, you most likely should be using
* {@link java.util.concurrent.ConcurrentHashMap} instead.
*
* This table supports strong, weak, and soft keys and values. By default keys
* are weak, and values are strong. Such a configuration offers similar behavior
* to {@link java.util.WeakHashMap}, entries of this table are periodically
* removed once their corresponding keys are no longer referenced outside of
* this table. In other words, this table will not prevent a key from being
* discarded by the garbage collector. Once a key has been discarded by the
* collector, the corresponding entry is no longer visible to this table;
* however, the entry may occupy space until a future table operation decides to
* reclaim it. For this reason, summary functions such as <tt>size</tt> and
* <tt>isEmpty</tt> might return a value greater than the observed number of
* entries. In order to support a high level of concurrency, stale entries are
* only reclaimed during blocking (usually mutating) operations.
*
* Enabling soft keys allows entries in this table to remain until their space
* is absolutely needed by the garbage collector. This is unlike weak keys which
* can be reclaimed as soon as they are no longer referenced by a normal strong
* reference. The primary use case for soft keys is a cache, which ideally
* occupies memory that is not in use for as long as possible.
*
* By default, values are held using a normal strong reference. This provides
* the commonly desired guarantee that a value will always have at least the
* same life-span as it's key. For this reason, care should be taken to ensure
* that a value never refers, either directly or indirectly, to its key, thereby
* preventing reclamation. If this is unavoidable, then it is recommended to use
* the same reference type in use for the key. However, it should be noted that
* non-strong values may disappear before their corresponding key.
*
* While this table does allow the use of both strong keys and values, it is
* recommended to use {@link java.util.concurrent.ConcurrentHashMap} for such a
* configuration, since it is optimized for that case.
*
* Just like {@link java.util.concurrent.ConcurrentHashMap}, 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>.
*
* @author Doug Lea
* @author Jason T. Greene
* @param <K> the type of keys maintained by this map
* @param <V> the type of mapped values
*/
@
SuppressWarnings("all")
public class
ConcurrentReferenceHashMap<K, V> extends
AbstractMap<K, V>
implements java.util.concurrent.
ConcurrentMap<K, V>,
Serializable {
private static final long
serialVersionUID = 7249069246763182397L;
/*
* The basic strategy is to subdivide the table among Segments,
* each of which itself is a concurrently readable hash table.
*/
/**
* An option specifying which Java reference type should be used to refer
* to a key and/or value.
*/
public static enum
ReferenceType {
/** Indicates a normal Java strong reference should be used */
STRONG,
/** Indicates a {@link WeakReference} should be used */
WEAK,
/** Indicates a {@link SoftReference} should be used */
SOFT
};
public static enum
Option {
/** Indicates that referential-equality (== instead of .equals()) should
* be used when locating keys. This offers similar behavior to {@link IdentityHashMap} */
IDENTITY_COMPARISONS
};
/* ---------------- Constants -------------- */
static final
ReferenceType DEFAULT_KEY_TYPE =
ReferenceType.
WEAK;
static final
ReferenceType DEFAULT_VALUE_TYPE =
ReferenceType.
STRONG;
/**
* 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 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;
boolean
identityComparisons;
transient
Set<K>
keySet;
transient
Set<
Map.
Entry<K,V>>
entrySet;
transient
Collection<V>
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<K,V>
segmentFor(int
hash) {
return
segments[(
hash >>>
segmentShift) &
segmentMask];
}
private int
hashOf(
Object key) {
return
hash(
identityComparisons ?
System.
identityHashCode(
key) :
key.
hashCode());
}
/* ---------------- Inner Classes -------------- */
static interface
KeyReference {
int
keyHash();
Object keyRef();
}
/**
* A weak-key reference which stores the key hash needed for reclamation.
*/
static final class
WeakKeyReference<K> extends
WeakReference<K> implements
KeyReference {
final int
hash;
WeakKeyReference(K
key, int
hash,
ReferenceQueue<
Object>
refQueue) {
super(
key,
refQueue);
this.
hash =
hash;
}
public final int
keyHash() {
return
hash;
}
public final
Object keyRef() {
return this;
}
}
/**
* A soft-key reference which stores the key hash needed for reclamation.
*/
static final class
SoftKeyReference<K> extends
SoftReference<K> implements
KeyReference {
final int
hash;
SoftKeyReference(K
key, int
hash,
ReferenceQueue<
Object>
refQueue) {
super(
key,
refQueue);
this.
hash =
hash;
}
public final int
keyHash() {
return
hash;
}
public final
Object keyRef() {
return this;
}
}
static final class
WeakValueReference<V> extends
WeakReference<V> implements
KeyReference {
final
Object keyRef;
final int
hash;
WeakValueReference(V
value,
Object keyRef, int
hash,
ReferenceQueue<
Object>
refQueue) {
super(
value,
refQueue);
this.
keyRef =
keyRef;
this.
hash =
hash;
}
public final int
keyHash() {
return
hash;
}
public final
Object keyRef() {
return
keyRef;
}
}
static final class
SoftValueReference<V> extends
SoftReference<V> implements
KeyReference {
final
Object keyRef;
final int
hash;
SoftValueReference(V
value,
Object keyRef, int
hash,
ReferenceQueue<
Object>
refQueue) {
super(
value,
refQueue);
this.
keyRef =
keyRef;
this.
hash =
hash;
}
public final int
keyHash() {
return
hash;
}
public final
Object keyRef() {
return
keyRef;
}
}
/**
* 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<K,V> {
final
Object keyRef;
final int
hash;
volatile
Object valueRef;
final
HashEntry<K,V>
next;
HashEntry(K
key, int
hash,
HashEntry<K,V>
next, V
value,
ReferenceType keyType,
ReferenceType valueType,
ReferenceQueue<
Object>
refQueue) {
this.
hash =
hash;
this.
next =
next;
this.
keyRef =
newKeyReference(
key,
keyType,
refQueue);
this.
valueRef =
newValueReference(
value,
valueType,
refQueue);
}
final
Object newKeyReference(K
key,
ReferenceType keyType,
ReferenceQueue<
Object>
refQueue) {
if (
keyType ==
ReferenceType.
WEAK)
return new
WeakKeyReference<K>(
key,
hash,
refQueue);
if (
keyType ==
ReferenceType.
SOFT)
return new
SoftKeyReference<K>(
key,
hash,
refQueue);
return
key;
}
final
Object newValueReference(V
value,
ReferenceType valueType,
ReferenceQueue<
Object>
refQueue) {
if (
valueType ==
ReferenceType.
WEAK)
return new
WeakValueReference<V>(
value,
keyRef,
hash,
refQueue);
if (
valueType ==
ReferenceType.
SOFT)
return new
SoftValueReference<V>(
value,
keyRef,
hash,
refQueue);
return
value;
}
@
SuppressWarnings("unchecked")
final K
key() {
if (
keyRef instanceof
KeyReference)
return ((
Reference<K>)
keyRef).
get();
return (K)
keyRef;
}
final V
value() {
return
dereferenceValue(
valueRef);
}
@
SuppressWarnings("unchecked")
final V
dereferenceValue(
Object value) {
if (
value instanceof
KeyReference)
return ((
Reference<V>)
value).
get();
return (V)
value;
}
final void
setValue(V
value,
ReferenceType valueType,
ReferenceQueue<
Object>
refQueue) {
this.
valueRef =
newValueReference(
value,
valueType,
refQueue);
}
@
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;
/**
* The collected weak-key reference queue for this segment.
* This should be (re)initialized whenever table is assigned,
*/
transient volatile
ReferenceQueue<
Object>
refQueue;
final
ReferenceType keyType;
final
ReferenceType valueType;
final boolean
identityComparisons;
Segment(int
initialCapacity, float
lf,
ReferenceType keyType,
ReferenceType valueType, boolean
identityComparisons) {
loadFactor =
lf;
this.
keyType =
keyType;
this.
valueType =
valueType;
this.
identityComparisons =
identityComparisons;
setTable(
HashEntry.<K,V>
newArray(
initialCapacity));
}
@
SuppressWarnings("unchecked")
static final <K,V>
Segment<K,V>[]
newArray(int
i) {
return new
Segment[
i];
}
private boolean
keyEq(
Object src,
Object dest) {
return
identityComparisons ?
src ==
dest :
src.
equals(
dest);
}
/**
* 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;
refQueue = new
ReferenceQueue<
Object>();
}
/**
* 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)];
}
HashEntry<K,V>
newHashEntry(K
key, int
hash,
HashEntry<K, V>
next, V
value) {
return new
HashEntry<K,V>(
key,
hash,
next,
value,
keyType,
valueType,
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<K,V>
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<K,V>
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<K,V>
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<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) {
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<K,V>
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,
valueType,
refQueue);
}
return
replaced;
} finally {
unlock();
}
}
V
replace(K
key, int
hash, V
newValue) {
lock();
try {
removeStale();
HashEntry<K,V>
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,
valueType,
refQueue);
}
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) // adjust from possible weak cleanups
count = (
c -=
reduced) - 1; // write-volatile
}
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 || !
keyEq(
key,
e.
key())))
e =
e.
next;
V
oldValue;
if (
e != null) {
oldValue =
e.
value();
if (!
onlyIfAbsent)
e.
setValue(
value,
valueType,
refQueue);
}
else {
oldValue = null;
++
modCount;
tab[
index] =
newHashEntry(
key,
hash,
first,
value);
count =
c; // write-volatile
}
return
oldValue;
} finally {
unlock();
}
}
int
rehash() {
HashEntry<K,V>[]
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<K,V>[]
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<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) {
// Skip GC'd weak refs
K
key =
p.
key();
if (
key == null) {
reduce++;
continue;
}
int
k =
p.
hash &
sizeMask;
HashEntry<K,V>
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<K,V>[]
tab =
table;
int
index =
hash & (
tab.length - 1);
HashEntry<K,V>
first =
tab[
index];
HashEntry<K,V>
e =
first;
// a ref 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<K,V>
newFirst =
e.
next;
for (
HashEntry<K,V>
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();
}
}
final void
removeStale() {
KeyReference ref;
while ((
ref = (
KeyReference)
refQueue.
poll()) != null) {
remove(
ref.
keyRef(),
ref.
keyHash(), null, true);
}
}
void
clear() {
if (
count != 0) {
lock();
try {
HashEntry<K,V>[]
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<
Object>();
count = 0; // write-volatile
} finally {
unlock();
}
}
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the specified initial
* capacity, reference types, load factor and concurrency level.
*
* Behavioral changing options such as {@link Option#IDENTITY_COMPARISONS}
* can also be specified.
*
* @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.
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @param options the behavioral options
* @throws IllegalArgumentException if the initial capacity is
* negative or the load factor or concurrencyLevel are
* nonpositive.
*/
public
ConcurrentReferenceHashMap(int
initialCapacity,
float
loadFactor, int
concurrencyLevel,
ReferenceType keyType,
ReferenceType valueType,
EnumSet<
Option>
options) {
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;
identityComparisons =
options != null &&
options.
contains(
Option.
IDENTITY_COMPARISONS);
for (int
i = 0;
i < this.
segments.length; ++
i)
this.
segments[
i] = new
Segment<K,V>(
cap,
loadFactor,
keyType,
valueType,
identityComparisons);
}
/**
* 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
ConcurrentReferenceHashMap(int
initialCapacity,
float
loadFactor, int
concurrencyLevel) {
this(
initialCapacity,
loadFactor,
concurrencyLevel,
DEFAULT_KEY_TYPE,
DEFAULT_VALUE_TYPE, null);
}
/**
* 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
*
* @since 1.6
*/
public
ConcurrentReferenceHashMap(int
initialCapacity, float
loadFactor) {
this(
initialCapacity,
loadFactor,
DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the specified initial capacity,
* reference types 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.
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @throws IllegalArgumentException if the initial capacity of
* elements is negative.
*/
public
ConcurrentReferenceHashMap(int
initialCapacity,
ReferenceType keyType,
ReferenceType valueType) {
this(
initialCapacity,
DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL,
keyType,
valueType, null);
}
/**
* Creates a new, empty reference map with the specified key
* and value reference types.
*
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @throws IllegalArgumentException if the initial capacity of
* elements is negative.
*/
public
ConcurrentReferenceHashMap(
ReferenceType keyType,
ReferenceType valueType) {
this(
DEFAULT_INITIAL_CAPACITY,
DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL,
keyType,
valueType, null);
}
/**
* Creates a new, empty reference map with the specified reference types
* and behavioral options.
*
* @param keyType the reference type to use for keys
* @param valueType the reference type to use for values
* @throws IllegalArgumentException if the initial capacity of
* elements is negative.
*/
public
ConcurrentReferenceHashMap(
ReferenceType keyType,
ReferenceType valueType,
EnumSet<
Option>
options) {
this(
DEFAULT_INITIAL_CAPACITY,
DEFAULT_LOAD_FACTOR,
DEFAULT_CONCURRENCY_LEVEL,
keyType,
valueType,
options);
}
/**
* 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
ConcurrentReferenceHashMap(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
ConcurrentReferenceHashMap() {
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
ConcurrentReferenceHashMap(
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 =
hashOf(
key);
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 =
hashOf(
key);
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 =
hashOf(
key);
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 =
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
*/
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 =
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 <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 =
hashOf(
key);
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();
}
/**
* 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 <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;
K
currentKey; // Strong reference to weak key (prevents gc)
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() {
while (
nextEntry != null) {
if (
nextEntry.
key() != null)
return true;
advance();
}
return false;
}
HashEntry<K,V>
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();
ConcurrentReferenceHashMap.this.
remove(
currentKey);
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(); }
}
/*
* This class is needed for JDK5 compatibility.
*/
static class
SimpleEntry<K, V> implements
Entry<K, V>,
java.io.
Serializable {
private static final long
serialVersionUID = -8499721149061103585L;
private final K
key;
private V
value;
public
SimpleEntry(K
key, V
value) {
this.
key =
key;
this.
value =
value;
}
public
SimpleEntry(
Entry<? extends K, ? extends V>
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;
}
public boolean
equals(
Object o) {
if (!(
o instanceof
Map.
Entry))
return false;
@
SuppressWarnings("unchecked")
Map.
Entry e = (
Map.
Entry)
o;
return
eq(
key,
e.
getKey()) &&
eq(
value,
e.
getValue());
}
public int
hashCode() {
return (
key == null ? 0 :
key.
hashCode())
^ (
value == null ? 0 :
value.
hashCode());
}
public
String toString() {
return
key + "=" +
value;
}
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<K,V>
{
private static final long
serialVersionUID = -7900634345345313646L;
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);
ConcurrentReferenceHashMap.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
ConcurrentReferenceHashMap.this.
size();
}
public boolean
isEmpty() {
return
ConcurrentReferenceHashMap.this.
isEmpty();
}
public boolean
contains(
Object o) {
return
ConcurrentReferenceHashMap.this.
containsKey(
o);
}
public boolean
remove(
Object o) {
return
ConcurrentReferenceHashMap.this.
remove(
o) != null;
}
public void
clear() {
ConcurrentReferenceHashMap.this.
clear();
}
}
final class
Values extends
AbstractCollection<V> {
public
Iterator<V>
iterator() {
return new
ValueIterator();
}
public int
size() {
return
ConcurrentReferenceHashMap.this.
size();
}
public boolean
isEmpty() {
return
ConcurrentReferenceHashMap.this.
isEmpty();
}
public boolean
contains(
Object o) {
return
ConcurrentReferenceHashMap.this.
containsValue(
o);
}
public void
clear() {
ConcurrentReferenceHashMap.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 =
ConcurrentReferenceHashMap.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
ConcurrentReferenceHashMap.this.
remove(
e.
getKey(),
e.
getValue());
}
public int
size() {
return
ConcurrentReferenceHashMap.this.
size();
}
public boolean
isEmpty() {
return
ConcurrentReferenceHashMap.this.
isEmpty();
}
public void
clear() {
ConcurrentReferenceHashMap.this.
clear();
}
}
/* ---------------- Serialization Support -------------- */
/**
* Save the state of the <tt>ConcurrentReferenceHashMap</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) {
K
key =
e.
key();
if (
key == null) // Skip GC'd keys
continue;
s.
writeObject(
key);
s.
writeObject(
e.
value());
}
}
} finally {
seg.
unlock();
}
}
s.
writeObject(null);
s.
writeObject(null);
}
/**
* Reconstitute the <tt>ConcurrentReferenceHashMap</tt> instance from a
* stream (i.e., deserialize it).
* @param s the stream
*/
@
SuppressWarnings("unchecked")
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);
}
}
}