/*
* Licensed to the Apache Software Foundation (ASF) under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional information regarding
* copyright ownership. The ASF 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.
*/
/**
*
*/
package org.apache.geode.internal;
/*
* 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.util.concurrent.locks.*;
import java.util.*;
import java.io.Serializable;
import java.io.IOException;
/**
* A hash table supporting full concurrency of retrievals and adjustable expected concurrency for
* updates. This class obeys the same functional specification as {@link java.util.Hashtable}, and
* includes versions of methods corresponding to each method of <tt>Hashtable</tt>. However, even
* though all operations are thread-safe, retrieval operations do <em>not</em> entail locking, and
* there is <em>not</em> any support for locking the entire table in a way that prevents all access.
* This class is fully interoperable with <tt>Hashtable</tt> in programs that rely on its thread
* safety but not on its synchronization details.
*
* <p>
* Retrieval operations (including <tt>get</tt>) generally do not block, so may overlap with update
* operations (including <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results of the
* most recently <em>completed</em> update operations holding upon their onset. For aggregate
* operations such as <tt>putAll</tt> and <tt>clear</tt>, concurrent retrievals may reflect
* insertion or removal of only some entries. Similarly, Iterators and Enumerations return elements
* reflecting the state of the hash table at some point at or since the creation of the
* iterator/enumeration. They do <em>not</em> throw {@link ConcurrentModificationException}.
* However, iterators are designed to be used by only one thread at a time.
*
* <p>
* The allowed concurrency among update operations is guided by the optional
* <tt>concurrencyLevel</tt> constructor argument (default <tt>16</tt>), which is used as a hint for
* internal sizing. The table is internally partitioned to try to permit the indicated number of
* concurrent updates without contention. Because placement in hash tables is essentially random,
* the actual concurrency will vary. Ideally, you should choose a value to accommodate as many
* threads as will ever concurrently modify the table. Using a significantly higher value than you
* need can waste space and time, and a significantly lower value can lead to thread contention. But
* overestimates and underestimates within an order of magnitude do not usually have much noticeable
* impact. A value of one is appropriate when it is known that only one thread will modify and all
* others will only read. Also, resizing this or any other kind of hash table is a relatively slow
* operation, so, when possible, it is a good idea to provide estimates of expected table sizes in
* constructors.
*
* <p>
* This class and its views and iterators implement all of the <em>optional</em> methods of the
* {@link Map} and {@link Iterator} interfaces.
*
* <p>
* Like {@link Hashtable} but unlike {@link HashMap}, this class does <em>not</em> allow
* <tt>null</tt> to be used as a key or value.
*
* <p>
* This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @since GemFire 1.5
* @param <V> the type of mapped values
*
* Keys on this map are a primitive "int".
*/
public class ObjIdConcurrentMap<V> /* extends AbstractMap<K, V> */
implements /* ConcurrentMap<K, V>, */ Serializable {
private static final long serialVersionUID = 7249069246763182397L;
/*
* The basic strategy is to subdivide the table among Segments, each of which itself is a
* concurrently readable hash table.
*/
/* ---------------- Constants -------------- */
/**
* The default initial 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<V>[] segments;
// transient Set keySet;
// transient Set<Entry<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 ConcurrentHashMap uses power-of-two length hash
* tables, that otherwise encounter collisions for hashCodes that do not differ in lower or upper
* bits.
*/
private static int hash(int h) {
// Spread bits to regularize both segment and index locations,
// using variant of single-word Wang/Jenkins hash.
h += (h << 15) ^ 0xffffcd7d;
h ^= (h >>> 10);
h += (h << 3);
h ^= (h >>> 6);
h += (h << 2) + (h << 14);
return h ^ (h >>> 16);
}
/**
* Returns the segment that should be used for key with given hash
*
* @param hash the hash code for the key
* @return the segment
*/
final Segment<V> segmentFor(int hash) {
return segments[(hash >>> segmentShift) & segmentMask];
}
/* ---------------- Inner Classes -------------- */
/**
* ConcurrentHashMap list entry. Note that this is never exported out as a user-visible Map.Entry.
*
* Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an
* unsynchronized reader to see null instead of initial value when read via a data race. Although
* a reordering leading to this is not likely to ever actually occur, the
* Segment.readValueUnderLock method is used as a backup in case a null (pre-initialized) value is
* ever seen in an unsynchronized access method.
*/
static final class HashEntry<V> {
final int key;
final int hash;
volatile V value;
final HashEntry<V> next;
HashEntry(int key, int hash, HashEntry<V> next, V value) {
this.key = key;
this.hash = hash;
this.next = next;
this.value = value;
}
@SuppressWarnings("unchecked")
static final <V> HashEntry<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<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<V>[] table;
/**
* The load factor for the hash table. Even though this value is same for all segments, it is
* replicated to avoid needing links to outer object.
*
* @serial
*/
final float loadFactor;
Segment(int initialCapacity, float lf) {
loadFactor = lf;
setTable(HashEntry.<V>newArray(initialCapacity));
}
@SuppressWarnings("unchecked")
static final <K, V> Segment<V>[] newArray(int i) {
return new Segment[i];
}
/**
* Sets table to new HashEntry array. Call only while holding lock or in constructor.
*/
void setTable(HashEntry<V>[] newTable) {
threshold = (int) (newTable.length * loadFactor);
table = newTable;
}
/**
* Returns properly casted first entry of bin for given hash.
*/
HashEntry<V> getFirst(int hash) {
HashEntry<V>[] tab = table;
return tab[hash & (tab.length - 1)];
}
/**
* Reads value field of an entry under lock. Called if value field ever appears to be null. This
* is possible only if a compiler happens to reorder a HashEntry initialization with its table
* assignment, which is legal under memory model but is not known to ever occur.
*/
V readValueUnderLock(HashEntry<V> e) {
lock();
try {
return e.value;
} finally {
unlock();
}
}
/* Specialized implementations of map methods */
V get(int key, int hash) {
if (count != 0) { // read-volatile
HashEntry<V> e = getFirst(hash);
while (e != null) {
if (e.hash == hash && key == e.key) {
V v = e.value;
if (v != null)
return v;
return readValueUnderLock(e); // recheck
}
e = e.next;
}
}
return null;
}
boolean containsKey(int key, int hash) {
if (count != 0) { // read-volatile
HashEntry<V> e = getFirst(hash);
while (e != null) {
if (e.hash == hash && key == e.key)
return true;
e = e.next;
}
}
return false;
}
boolean containsValue(Object value) {
if (count != 0) { // read-volatile
HashEntry<V>[] tab = table;
int len = tab.length;
for (int i = 0; i < len; i++) {
for (HashEntry<V> e = tab[i]; e != null; e = e.next) {
V v = e.value;
if (v == null) // recheck
v = readValueUnderLock(e);
if (value.equals(v))
return true;
}
}
}
return false;
}
boolean replace(int key, int hash, V oldValue, V newValue) {
lock();
try {
HashEntry<V> e = getFirst(hash);
while (e != null && (e.hash != hash || key != e.key))
e = e.next;
boolean replaced = false;
if (e != null && oldValue.equals(e.value)) {
replaced = true;
e.value = newValue;
}
return replaced;
} finally {
unlock();
}
}
V replace(int key, int hash, V newValue) {
lock();
try {
HashEntry<V> e = getFirst(hash);
while (e != null && (e.hash != hash || key != e.key))
e = e.next;
V oldValue = null;
if (e != null) {
oldValue = e.value;
e.value = newValue;
}
return oldValue;
} finally {
unlock();
}
}
V put(int key, int hash, V value, boolean onlyIfAbsent) {
lock();
try {
int c = count;
if (c++ > threshold) // ensure capacity
rehash();
HashEntry<V>[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<V> first = tab[index];
HashEntry<V> e = first;
while (e != null && (e.hash != hash || key != e.key))
e = e.next;
V oldValue;
if (e != null) {
oldValue = e.value;
if (!onlyIfAbsent)
e.value = value;
} else {
oldValue = null;
++modCount;
tab[index] = new HashEntry<V>(key, hash, first, value);
count = c; // write-volatile
}
return oldValue;
} finally {
unlock();
}
}
void rehash() {
HashEntry<V>[] oldTable = table;
int oldCapacity = oldTable.length;
if (oldCapacity >= MAXIMUM_CAPACITY)
return;
/*
* Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the
* elements from each bin must either stay at same index, or move with a power of two offset.
* We eliminate unnecessary node creation by catching cases where old nodes can be reused
* because their next fields won't change. Statistically, at the default threshold, only about
* one-sixth of them need cloning when a table doubles. The nodes they replace will be garbage
* collectable as soon as they are no longer referenced by any reader thread that may be in
* the midst of traversing table right now.
*/
HashEntry<V>[] newTable = HashEntry.newArray(oldCapacity << 1);
threshold = (int) (newTable.length * loadFactor);
int sizeMask = newTable.length - 1;
for (int i = 0; i < oldCapacity; i++) {
// We need to guarantee that any existing reads of old Map can
// proceed. So we cannot yet null out each bin.
HashEntry<V> e = oldTable[i];
if (e != null) {
HashEntry<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<V> lastRun = e;
int lastIdx = idx;
for (HashEntry<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<V> p = e; p != lastRun; p = p.next) {
int k = p.hash & sizeMask;
HashEntry<V> n = newTable[k];
newTable[k] = new HashEntry<V>(p.key, p.hash, n, p.value);
}
}
}
}
table = newTable;
}
/**
* Remove; match on key only if value null, else match both.
*/
V remove(int key, int hash, Object value) {
lock();
try {
int c = count - 1;
HashEntry<V>[] tab = table;
int index = hash & (tab.length - 1);
HashEntry<V> first = tab[index];
HashEntry<V> e = first;
while (e != null && (e.hash != hash || 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<V> newFirst = e.next;
for (HashEntry<V> p = first; p != e; p = p.next)
newFirst = new HashEntry<V>(p.key, p.hash, newFirst, p.value);
tab[index] = newFirst;
count = c; // write-volatile
}
}
return oldValue;
} finally {
unlock();
}
}
void clear() {
if (count != 0) {
lock();
try {
HashEntry<V>[] tab = table;
for (int i = 0; i < tab.length; i++)
tab[i] = null;
++modCount;
count = 0; // write-volatile
} finally {
unlock();
}
}
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the specified initial capacity, load factor and concurrency
* level.
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to
* accommodate this many elements.
* @param loadFactor the load factor threshold, used to control resizing. Resizing may be
* performed when the average number of elements per bin exceeds this threshold.
* @param concurrencyLevel the estimated number of concurrently updating threads. The
* implementation performs internal sizing to try to accommodate this many threads.
* @throws IllegalArgumentException if the initial capacity is negative or the load factor or
* concurrencyLevel are nonpositive.
*/
public ObjIdConcurrentMap(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<V>(cap, loadFactor);
}
/**
* Creates a new, empty map with the specified initial capacity and load factor and with the
* default concurrencyLevel (16).
*
* @param initialCapacity The implementation performs internal sizing to accommodate this many
* elements.
* @param loadFactor the load factor threshold, used to control resizing. Resizing may be
* performed when the average number of elements per bin exceeds this threshold.
* @throws IllegalArgumentException if the initial capacity of elements is negative or the load
* factor is nonpositive
*
* @since GemFire 1.6
*/
public ObjIdConcurrentMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the specified initial capacity, and with default load factor
* (0.75) and concurrencyLevel (16).
*
* @param initialCapacity the initial capacity. The implementation performs internal sizing to
* accommodate this many elements.
* @throws IllegalArgumentException if the initial capacity of elements is negative.
*/
public ObjIdConcurrentMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with a default initial capacity (16), load factor (0.75) and
* concurrencyLevel (16).
*/
public ObjIdConcurrentMap() {
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 ObjIdConcurrentMap(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<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<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(int key) {
int hash = hash(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(int key) {
int hash = hash(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<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(int key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).put(key, hash, value, false);
}
/**
*
* @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(int key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).put(key, hash, value, true);
}
/**
* Copies all of the mappings from the specified map to this one. These mappings replace any
* mappings that this map had for any of the keys currently in the specified map.
*
* @param 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(int key) {
int hash = hash(key);
return segmentFor(hash).remove(key, hash, null);
}
/**
*
* @throws NullPointerException if the specified key is null
*/
public boolean remove(int key, Object value) {
int hash = hash(key);
if (value == null)
return false;
return segmentFor(hash).remove(key, hash, value) != null;
}
/**
*
* @throws NullPointerException if any of the arguments are null
*/
public boolean replace(int key, V oldValue, V newValue) {
if (oldValue == null || newValue == null)
throw new NullPointerException();
int hash = hash(key);
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
*
* @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(int key, V value) {
if (value == null)
throw new NullPointerException();
int hash = hash(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();
}
/*
* 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<V>[] currentTable;
HashEntry<V> nextEntry;
HashEntry<V> lastReturned;
HashIterator() {
nextSegmentIndex = segments.length - 1;
nextTableIndex = -1;
advance();
}
public boolean hasMoreElements() {
return hasNext();
}
final void advance() {
if (nextEntry != null && (nextEntry = nextEntry.next) != null)
return;
while (nextTableIndex >= 0) {
if ((nextEntry = currentTable[nextTableIndex--]) != null)
return;
}
while (nextSegmentIndex >= 0) {
Segment<V> seg = segments[nextSegmentIndex--];
if (seg.count != 0) {
currentTable = seg.table;
for (int j = currentTable.length - 1; j >= 0; --j) {
if ((nextEntry = currentTable[j]) != null) {
nextTableIndex = j - 1;
return;
}
}
}
}
}
public boolean hasNext() {
return nextEntry != null;
}
HashEntry<V> nextEntry() {
if (nextEntry == null)
throw new NoSuchElementException();
lastReturned = nextEntry;
advance();
return lastReturned;
}
public void remove() {
if (lastReturned == null)
throw new IllegalStateException();
ObjIdConcurrentMap.this.remove(lastReturned.key);
lastReturned = null;
}
}
/*
* final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> { public K
* next() { return super.nextEntry().key; } public K nextElement() { return super.nextEntry().key;
* } }
*
* final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> { public
* V next() { return super.nextEntry().value; } public V nextElement() { return
* super.nextEntry().value; } }
*/
// interface Entry<V> {
// int getKey();
// V getValue();
// V setValue(V value);
// boolean equals(Object o);
// int hashCode();
// }
// static class SimpleEntry<V> implements Entry<V> {
// int key;
// V value;
//
// public SimpleEntry(int key, V value) {
// this.key = key;
// this.value = value;
// }
//
// public SimpleEntry(Entry<V> e) {
// this.key = e.getKey();
// this.value = e.getValue();
// }
//
// public int 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;
// Map.Entry<?, ?> e = (Map.Entry<?, ?>)o;
// return eq(key, e.getKey()) && eq(value, e.getValue());
// }
//
// @Override
// public int hashCode() {
// return (key) ^
// ((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<V>
// {
// WriteThroughEntry(int 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.
// */
// @Override
// public V setValue(V value) {
// if (value == null) throw new NullPointerException();
// V v = super.setValue(value);
// ObjIdConcurrentMap.this.put(getKey(), value);
// return v;
// }
// }
/*
* final class EntryIterator extends HashIterator implements Iterator<Entry<V>> { public Entry<V>
* next() { HashEntry<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 ObjIdConcurrentMap.this.size(); } public boolean
* isEmpty() { return ObjIdConcurrentMap.this.isEmpty(); } public boolean contains(Object o) {
* return ObjIdConcurrentMap.this.containsKey(o); } public boolean remove(Object o) { return
* ObjIdConcurrentMap.this.remove(o) != null; } public void clear() {
* ObjIdConcurrentMap.this.clear(); } }
*
* final class Values extends AbstractCollection<V> { public Iterator<V> iterator() { return new
* ValueIterator(); } public int size() { return ObjIdConcurrentMap.this.size(); } public boolean
* isEmpty() { return ObjIdConcurrentMap.this.isEmpty(); } public boolean contains(Object o) {
* return ObjIdConcurrentMap.this.containsValue(o); } public void clear() {
* ObjIdConcurrentMap.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 =
* ObjIdConcurrentMap.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 ObjIdConcurrentMap.this.remove(e.getKey(), e.getValue()); } public
* int size() { return ObjIdConcurrentMap.this.size(); } public boolean isEmpty() { return
* ObjIdConcurrentMap.this.isEmpty(); } public void clear() { ObjIdConcurrentMap.this.clear(); } }
*/
/* ---------------- Serialization Support -------------- */
/**
* Save the state of the <tt>ConcurrentHashMap</tt> instance to a stream (i.e., serialize it).
*
* @param s the stream
* @serialData the key (Object) and value (Object) for each key-value mapping, followed by a null
* pair. The key-value mappings are emitted in no particular order.
*/
private void writeObject(java.io.ObjectOutputStream s) throws IOException {
s.defaultWriteObject();
for (int k = 0; k < segments.length; ++k) {
Segment<V> seg = segments[k];
seg.lock();
try {
HashEntry<V>[] tab = seg.table;
for (int i = 0; i < tab.length; ++i) {
for (HashEntry<V> e = tab[i]; e != null; e = e.next) {
s.writeObject(e.key);
s.writeObject(e.value);
}
}
} finally {
seg.unlock();
}
}
s.writeObject(null);
s.writeObject(null);
}
/**
* Reconstitute the <tt>ConcurrentHashMap</tt> instance from a stream (i.e., deserialize it).
*
* @param s the stream
*/
@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 (;;) {
int key = s.readInt();
V value = (V) s.readObject();
// if (key == null)
// break;
put(key, value);
}
}
}