org.hibernate.internal.util.collections.BoundedConcurrentHashMap Maven / Gradle / Ivy
/*
* JBoss, Home of Professional Open Source
* Copyright 2010 Red Hat Inc. and/or its affiliates and other
* contributors as indicated by the @author tags. All rights reserved.
* See the copyright.txt in the distribution for a full listing of
* individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
/*
* 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
*
* Modified for https://jira.jboss.org/jira/browse/ISPN-299
* Includes ideas described in http://portal.acm.org/citation.cfm?id=1547428
*
*/
package org.hibernate.internal.util.collections;
import java.io.IOException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.ConcurrentModificationException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.locks.ReentrantLock;
import static java.util.Collections.singletonMap;
import static java.util.Collections.unmodifiableMap;
/**
* A hash table supporting full concurrency of retrievals and
* adjustable expected concurrency for updates. This class obeys the
* same functional specification as {@link Hashtable}, and
* includes versions of methods corresponding to each method of
* Hashtable. However, even though all operations are
* thread-safe, retrieval operations do not entail locking,
* and there is not any support for locking the entire table
* in a way that prevents all access. This class is fully
* interoperable with Hashtable in programs that rely on its
* thread safety but not on its synchronization details.
*
* Retrieval operations (including get) generally do not
* block, so may overlap with update operations (including
* put and remove). Retrievals reflect the results
* of the most recently completed update operations holding
* upon their onset. For aggregate operations such as putAll
* and clear, 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 not throw {@link ConcurrentModificationException}.
* However, iterators are designed to be used by only one thread at a time.
*
*
The allowed concurrency among update operations is guided by
* the optional concurrencyLevel constructor argument
* (default 16), 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.
*
*
This class and its views and iterators implement all of the
* optional methods of the {@link Map} and {@link Iterator}
* interfaces.
*
*
This class is copied from Infinispan, and was originally 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
*
*
* Like {@link Hashtable} but unlike {@link HashMap}, this class
* does not allow null to be used as a key or value.
*
* @author Doug Lea
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
public class BoundedConcurrentHashMap extends AbstractMap
implements ConcurrentMap, 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_MAXIMUM_CAPACITY = 512;
/**
* 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[] segments;
transient Set keySet;
transient Set> entrySet;
transient Collection 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 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.
*/
private static class HashEntry {
final K key;
final int hash;
volatile V value;
final HashEntry next;
HashEntry(K key, int hash, HashEntry next, V value) {
this.key = key;
this.hash = hash;
this.next = next;
this.value = value;
}
@Override
public int hashCode() {
int result = 17;
result = result * 31 + hash;
result = result * 31 + key.hashCode();
return result;
}
@Override
public boolean equals(Object o) {
// HashEntry is internal class, never leaks out of CHM, hence slight optimization
if (this == o) {
return true;
}
if (o == null) {
return false;
}
HashEntry other = (HashEntry) o;
return hash == other.hash && key.equals(other.key);
}
@SuppressWarnings("unchecked")
static HashEntry[] newArray(int i) {
return new HashEntry[i];
}
}
private enum Recency {
HIR_RESIDENT, LIR_RESIDENT, HIR_NONRESIDENT
}
public enum Eviction {
NONE {
@Override
public EvictionPolicy make(Segment s, int capacity, float lf) {
return new NullEvictionPolicy();
}
},
LRU {
@Override
public EvictionPolicy make(Segment s, int capacity, float lf) {
return new LRU(s,capacity,lf,capacity*10,lf);
}
},
LIRS {
@Override
public EvictionPolicy make(Segment s, int capacity, float lf) {
return new LIRS(s,capacity,capacity*10,lf);
}
};
abstract EvictionPolicy make(Segment s, int capacity, float lf);
}
public interface EvictionListener {
void onEntryEviction(Map evicted);
void onEntryChosenForEviction(V internalCacheEntry);
}
static final class NullEvictionListener implements EvictionListener {
@Override
public void onEntryEviction(Map evicted) {
// Do nothing.
}
@Override
public void onEntryChosenForEviction(V internalCacheEntry) {
// Do nothing.
}
}
public interface EvictionPolicy {
public final static int MAX_BATCH_SIZE = 64;
HashEntry createNewEntry(K key, int hash, HashEntry next, V value);
/**
* Invokes eviction policy algorithm and returns set of evicted entries.
*
*
* Set cannot be null but could possibly be an empty set.
*
* @return set of evicted entries.
*/
Set> execute();
/**
* Invoked to notify EvictionPolicy implementation that there has been an attempt to access
* an entry in Segment, however that entry was not present in Segment.
*
* @param e
* accessed entry in Segment
*
* @return non null set of evicted entries.
*/
Set> onEntryMiss(HashEntry e);
/**
* Invoked to notify EvictionPolicy implementation that an entry in Segment has been
* accessed. Returns true if batching threshold has been reached, false otherwise.
*
* Note that this method is potentially invoked without holding a lock on Segment.
*
* @return true if batching threshold has been reached, false otherwise.
*
* @param e
* accessed entry in Segment
*/
boolean onEntryHit(HashEntry e);
/**
* Invoked to notify EvictionPolicy implementation that an entry e has been removed from
* Segment.
*
* @param e
* removed entry in Segment
*/
void onEntryRemove(HashEntry e);
/**
* Invoked to notify EvictionPolicy implementation that all Segment entries have been
* cleared.
*
*/
void clear();
/**
* Returns type of eviction algorithm (strategy).
*
* @return type of eviction algorithm
*/
Eviction strategy();
/**
* Returns true if batching threshold has expired, false otherwise.
*
* Note that this method is potentially invoked without holding a lock on Segment.
*
* @return true if batching threshold has expired, false otherwise.
*/
boolean thresholdExpired();
}
static class NullEvictionPolicy implements EvictionPolicy {
@Override
public void clear() {
// Do nothing.
}
@Override
public Set> execute() {
return Collections.emptySet();
}
@Override
public boolean onEntryHit(HashEntry e) {
return false;
}
@Override
public Set> onEntryMiss(HashEntry e) {
return Collections.emptySet();
}
@Override
public void onEntryRemove(HashEntry e) {
// Do nothing.
}
@Override
public boolean thresholdExpired() {
return false;
}
@Override
public Eviction strategy() {
return Eviction.NONE;
}
@Override
public HashEntry createNewEntry(K key, int hash, HashEntry next, V value) {
return new HashEntry(key, hash, next, value);
}
}
static final class LRU extends LinkedHashMap, V> implements EvictionPolicy {
/** The serialVersionUID */
private static final long serialVersionUID = -7645068174197717838L;
private final ConcurrentLinkedQueue> accessQueue;
private final Segment segment;
private final int maxBatchQueueSize;
private final int trimDownSize;
private final float batchThresholdFactor;
private final Set> evicted;
public LRU(Segment s, int capacity, float lf, int maxBatchSize, float batchThresholdFactor) {
super(capacity, lf, true);
this.segment = s;
this.trimDownSize = capacity;
this.maxBatchQueueSize = maxBatchSize > MAX_BATCH_SIZE ? MAX_BATCH_SIZE : maxBatchSize;
this.batchThresholdFactor = batchThresholdFactor;
this.accessQueue = new ConcurrentLinkedQueue>();
this.evicted = new HashSet>();
}
@Override
public Set> execute() {
Set> evictedCopy = new HashSet>();
for (HashEntry e : accessQueue) {
put(e, e.value);
}
evictedCopy.addAll(evicted);
accessQueue.clear();
evicted.clear();
return evictedCopy;
}
@Override
public Set> onEntryMiss(HashEntry e) {
put(e, e.value);
if (!evicted.isEmpty()) {
Set> evictedCopy = new HashSet>();
evictedCopy.addAll(evicted);
evicted.clear();
return evictedCopy;
} else {
return Collections.emptySet();
}
}
/*
* Invoked without holding a lock on Segment
*/
@Override
public boolean onEntryHit(HashEntry e) {
accessQueue.add(e);
return accessQueue.size() >= maxBatchQueueSize * batchThresholdFactor;
}
/*
* Invoked without holding a lock on Segment
*/
@Override
public boolean thresholdExpired() {
return accessQueue.size() >= maxBatchQueueSize;
}
@Override
public void onEntryRemove(HashEntry e) {
remove(e);
// we could have multiple instances of e in accessQueue; remove them all
while (accessQueue.remove(e)) {
continue;
}
}
@Override
public void clear() {
super.clear();
accessQueue.clear();
}
@Override
public Eviction strategy() {
return Eviction.LRU;
}
protected boolean isAboveThreshold(){
return size() > trimDownSize;
}
protected boolean removeEldestEntry(Map.Entry,V> eldest){
boolean aboveThreshold = isAboveThreshold();
if(aboveThreshold){
HashEntry evictedEntry = eldest.getKey();
segment.evictionListener.onEntryChosenForEviction(evictedEntry.value);
segment.remove(evictedEntry.key, evictedEntry.hash, null);
evicted.add(evictedEntry);
}
return aboveThreshold;
}
@Override
public HashEntry createNewEntry(K key, int hash, HashEntry next, V value) {
return new HashEntry(key, hash, next, value);
}
}
/**
* Adapted to Infinispan BoundedConcurrentHashMap using LIRS implementation ideas from Charles Fry ([email protected])
* See http://code.google.com/p/concurrentlinkedhashmap/source/browse/trunk/src/test/java/com/googlecode/concurrentlinkedhashmap/caches/LirsMap.java
* for original sources
*
*/
private static final class LIRSHashEntry extends HashEntry {
// LIRS stack S
private LIRSHashEntry previousInStack;
private LIRSHashEntry nextInStack;
// LIRS queue Q
private LIRSHashEntry previousInQueue;
private LIRSHashEntry nextInQueue;
volatile Recency state;
LIRS owner;
LIRSHashEntry(LIRS owner, K key, int hash, HashEntry next, V value) {
super(key,hash,next,value);
this.owner = owner;
this.state = Recency.HIR_RESIDENT;
// initially point everything back to self
this.previousInStack = this;
this.nextInStack = this;
this.previousInQueue = this;
this.nextInQueue = this;
}
@Override
public int hashCode() {
int result = 17;
result = result * 31 + hash;
result = result * 31 + key.hashCode();
return result;
}
@Override
public boolean equals(Object o) {
// HashEntry is internal class, never leaks out of CHM, hence slight optimization
if (this == o) {
return true;
}
if (o == null) {
return false;
}
HashEntry other = (HashEntry) o;
return hash == other.hash && key.equals(other.key);
}
/**
* Returns true if this entry is in the stack, false otherwise.
*/
public boolean inStack() {
return (nextInStack != null);
}
/**
* Returns true if this entry is in the queue, false otherwise.
*/
public boolean inQueue() {
return (nextInQueue != null);
}
/**
* Records a cache hit.
*/
public void hit(Set> evicted) {
switch (state) {
case LIR_RESIDENT:
hotHit(evicted);
break;
case HIR_RESIDENT:
coldHit(evicted);
break;
case HIR_NONRESIDENT:
throw new IllegalStateException("Can't hit a non-resident entry!");
default:
throw new AssertionError("Hit with unknown status: " + state);
}
}
/**
* Records a cache hit on a hot block.
*/
private void hotHit(Set> evicted) {
// See section 3.3 case 1:
// "Upon accessing an LIR block X:
// This access is guaranteed to be a hit in the cache."
// "We move it to the top of stack S."
boolean onBottom = (owner.stackBottom() == this);
moveToStackTop();
// "If the LIR block is originally located in the bottom of the stack,
// we conduct a stack pruning."
if (onBottom) {
owner.pruneStack(evicted);
}
}
/**
* Records a cache hit on a cold block.
*/
private void coldHit(Set> evicted) {
// See section 3.3 case 2:
// "Upon accessing an HIR resident block X:
// This is a hit in the cache."
// "We move it to the top of stack S."
boolean inStack = inStack();
moveToStackTop();
// "There are two cases for block X:"
if (inStack) {
// "(1) If X is in the stack S, we change its status to LIR."
hot();
// "This block is also removed from list Q."
removeFromQueue();
// "The LIR block in the bottom of S is moved to the end of list Q
// with its status changed to HIR."
owner.stackBottom().migrateToQueue();
// "A stack pruning is then conducted."
owner.pruneStack(evicted);
} else {
// "(2) If X is not in stack S, we leave its status in HIR and move
// it to the end of list Q."
moveToQueueEnd();
}
}
/**
* Records a cache miss. This is how new entries join the LIRS stack and
* queue. This is called both when a new entry is first created, and when a
* non-resident entry is re-computed.
*/
private Set> miss() {
Set> evicted = Collections.emptySet();
if (owner.hotSize < owner.maximumHotSize) {
warmupMiss();
} else {
evicted = new HashSet>();
fullMiss(evicted);
}
// now the missed item is in the cache
owner.size++;
return evicted;
}
/**
* Records a miss when the hot entry set is not full.
*/
private void warmupMiss() {
// See section 3.3:
// "When LIR block set is not full, all the referenced blocks are
// given an LIR status until its size reaches L_lirs."
hot();
moveToStackTop();
}
/**
* Records a miss when the hot entry set is full.
*/
private void fullMiss(Set> evicted) {
// See section 3.3 case 3:
// "Upon accessing an HIR non-resident block X:
// This is a miss."
// This condition is unspecified in the paper, but appears to be
// necessary.
if (owner.size >= owner.maximumSize) {
// "We remove the HIR resident block at the front of list Q (it then
// becomes a non-resident block), and replace it out of the cache."
LIRSHashEntry evictedNode = owner.queueFront();
evicted.add(evictedNode);
}
// "Then we load the requested block X into the freed buffer and place
// it on the top of stack S."
boolean inStack = inStack();
moveToStackTop();
// "There are two cases for block X:"
if (inStack) {
// "(1) If X is in stack S, we change its status to LIR and move the
// LIR block in the bottom of stack S to the end of list Q with its
// status changed to HIR. A stack pruning is then conducted.
hot();
owner.stackBottom().migrateToQueue();
owner.pruneStack(evicted);
} else {
// "(2) If X is not in stack S, we leave its status in HIR and place
// it in the end of list Q."
cold();
}
}
/**
* Marks this entry as hot.
*/
private void hot() {
if (state != Recency.LIR_RESIDENT) {
owner.hotSize++;
}
state = Recency.LIR_RESIDENT;
}
/**
* Marks this entry as cold.
*/
private void cold() {
if (state == Recency.LIR_RESIDENT) {
owner.hotSize--;
}
state = Recency.HIR_RESIDENT;
moveToQueueEnd();
}
/**
* Marks this entry as non-resident.
*/
@SuppressWarnings("fallthrough")
private void nonResident() {
switch (state) {
case LIR_RESIDENT:
owner.hotSize--;
// fallthrough
case HIR_RESIDENT:
owner.size--;
break;
}
state = Recency.HIR_NONRESIDENT;
}
/**
* Returns true if this entry is resident in the cache, false otherwise.
*/
public boolean isResident() {
return (state != Recency.HIR_NONRESIDENT);
}
/**
* Temporarily removes this entry from the stack, fixing up neighbor links.
* This entry's links remain unchanged, meaning that {@link #inStack()} will
* continue to return true. This should only be called if this node's links
* will be subsequently changed.
*/
private void tempRemoveFromStack() {
if (inStack()) {
previousInStack.nextInStack = nextInStack;
nextInStack.previousInStack = previousInStack;
}
}
/**
* Removes this entry from the stack.
*/
private void removeFromStack() {
tempRemoveFromStack();
previousInStack = null;
nextInStack = null;
}
/**
* Inserts this entry before the specified existing entry in the stack.
*/
private void addToStackBefore(LIRSHashEntry existingEntry) {
previousInStack = existingEntry.previousInStack;
nextInStack = existingEntry;
previousInStack.nextInStack = this;
nextInStack.previousInStack = this;
}
/**
* Moves this entry to the top of the stack.
*/
private void moveToStackTop() {
tempRemoveFromStack();
addToStackBefore(owner.header.nextInStack);
}
/**
* Moves this entry to the bottom of the stack.
*/
private void moveToStackBottom() {
tempRemoveFromStack();
addToStackBefore(owner.header);
}
/**
* Temporarily removes this entry from the queue, fixing up neighbor links.
* This entry's links remain unchanged. This should only be called if this
* node's links will be subsequently changed.
*/
private void tempRemoveFromQueue() {
if (inQueue()) {
previousInQueue.nextInQueue = nextInQueue;
nextInQueue.previousInQueue = previousInQueue;
}
}
/**
* Removes this entry from the queue.
*/
private void removeFromQueue() {
tempRemoveFromQueue();
previousInQueue = null;
nextInQueue = null;
}
/**
* Inserts this entry before the specified existing entry in the queue.
*/
private void addToQueueBefore(LIRSHashEntry existingEntry) {
previousInQueue = existingEntry.previousInQueue;
nextInQueue = existingEntry;
previousInQueue.nextInQueue = this;
nextInQueue.previousInQueue = this;
}
/**
* Moves this entry to the end of the queue.
*/
private void moveToQueueEnd() {
tempRemoveFromQueue();
addToQueueBefore(owner.header);
}
/**
* Moves this entry from the stack to the queue, marking it cold
* (as hot entries must remain in the stack). This should only be called
* on resident entries, as non-resident entries should not be made resident.
* The bottom entry on the queue is always hot due to stack pruning.
*/
private void migrateToQueue() {
removeFromStack();
cold();
}
/**
* Moves this entry from the queue to the stack, marking it hot (as cold
* resident entries must remain in the queue).
*/
private void migrateToStack() {
removeFromQueue();
if (!inStack()) {
moveToStackBottom();
}
hot();
}
/**
* Evicts this entry, removing it from the queue and setting its status to
* cold non-resident. If the entry is already absent from the stack, it is
* removed from the backing map; otherwise it remains in order for its
* recency to be maintained.
*/
private void evict() {
removeFromQueue();
removeFromStack();
nonResident();
owner = null;
}
/**
* Removes this entry from the cache. This operation is not specified in
* the paper, which does not account for forced eviction.
*/
private V remove() {
boolean wasHot = (state == Recency.LIR_RESIDENT);
V result = value;
LIRSHashEntry end = owner != null? owner.queueEnd():null;
evict();
// attempt to maintain a constant number of hot entries
if (wasHot) {
if (end != null) {
end.migrateToStack();
}
}
return result;
}
}
static final class LIRS implements EvictionPolicy {
/**
* The percentage of the cache which is dedicated to hot blocks.
* See section 5.1
*/
private static final float L_LIRS = 0.95f;
/** The owning segment */
private final Segment segment;
/**
* The accessQueue for reducing lock contention
* See "BP-Wrapper: a system framework making any replacement algorithms
* (almost) lock contention free"
*
* http://www.cse.ohio-state.edu/hpcs/WWW/HTML/publications/abs09-1.html
*
* */
private final ConcurrentLinkedQueue> accessQueue;
/**
* The maxBatchQueueSize
*
* See "BP-Wrapper: a system framework making any replacement algorithms (almost) lock
* contention free"
* */
private final int maxBatchQueueSize;
/** The number of LIRS entries in a segment */
private int size;
private final float batchThresholdFactor;
/**
* This header encompasses two data structures:
*
*
* - The LIRS stack, S, which is maintains recency information. All hot
* entries are on the stack. All cold and non-resident entries which are more
* recent than the least recent hot entry are also stored in the stack (the
* stack is always pruned such that the last entry is hot, and all entries
* accessed more recently than the last hot entry are present in the stack).
* The stack is ordered by recency, with its most recently accessed entry
* at the top, and its least recently accessed entry at the bottom.
*
* - The LIRS queue, Q, which enqueues all cold entries for eviction. Cold
* entries (by definition in the queue) may be absent from the stack (due to
* pruning of the stack). Cold entries are added to the end of the queue
* and entries are evicted from the front of the queue.
*
*/
private final LIRSHashEntry header = new LIRSHashEntry(null, null,0,null,null);
/** The maximum number of hot entries (L_lirs in the paper). */
private final int maximumHotSize;
/** The maximum number of resident entries (L in the paper). */
private final int maximumSize ;
/** The actual number of hot entries. */
private int hotSize;
public LIRS(Segment s, int capacity, int maxBatchSize, float batchThresholdFactor) {
this.segment = s;
this.maximumSize = capacity;
this.maximumHotSize = calculateLIRSize(capacity);
this.maxBatchQueueSize = maxBatchSize > MAX_BATCH_SIZE ? MAX_BATCH_SIZE : maxBatchSize;
this.batchThresholdFactor = batchThresholdFactor;
this.accessQueue = new ConcurrentLinkedQueue>();
}
private static int calculateLIRSize(int maximumSize) {
int result = (int) (L_LIRS * maximumSize);
return (result == maximumSize) ? maximumSize - 1 : result;
}
@Override
public Set> execute() {
Set> evicted = new HashSet>();
try {
for (LIRSHashEntry e : accessQueue) {
if(e.isResident()){
e.hit(evicted);
}
}
removeFromSegment(evicted);
} finally {
accessQueue.clear();
}
return evicted;
}
/**
* Prunes HIR blocks in the bottom of the stack until an HOT block sits in
* the stack bottom. If pruned blocks were resident, then they
* remain in the queue; otherwise they are no longer referenced, and are thus
* removed from the backing map.
*/
private void pruneStack(Set> evicted) {
// See section 3.3:
// "We define an operation called "stack pruning" on the LIRS
// stack S, which removes the HIR blocks in the bottom of
// the stack until an LIR block sits in the stack bottom. This
// operation serves for two purposes: (1) We ensure the block in
// the bottom of the stack always belongs to the LIR block set.
// (2) After the LIR block in the bottom is removed, those HIR
// blocks contiguously located above it will not have chances to
// change their status from HIR to LIR, because their recencies
// are larger than the new maximum recency of LIR blocks."
LIRSHashEntry bottom = stackBottom();
while (bottom != null && bottom.state != Recency.LIR_RESIDENT) {
bottom.removeFromStack();
if (bottom.state == Recency.HIR_NONRESIDENT) {
evicted.add(bottom);
}
bottom = stackBottom();
}
}
@Override
public Set> onEntryMiss(HashEntry en) {
LIRSHashEntry e = (LIRSHashEntry) en;
Set> evicted = e.miss();
removeFromSegment(evicted);
return evicted;
}
private void removeFromSegment(Set> evicted) {
for (HashEntry e : evicted) {
((LIRSHashEntry)e).evict();
segment.evictionListener.onEntryChosenForEviction(e.value);
segment.remove(e.key, e.hash, null);
}
}
/*
* Invoked without holding a lock on Segment
*/
@Override
public boolean onEntryHit(HashEntry e) {
accessQueue.add((LIRSHashEntry) e);
return accessQueue.size() >= maxBatchQueueSize * batchThresholdFactor;
}
/*
* Invoked without holding a lock on Segment
*/
@Override
public boolean thresholdExpired() {
return accessQueue.size() >= maxBatchQueueSize;
}
@Override
public void onEntryRemove(HashEntry e) {
((LIRSHashEntry)e).remove();
// we could have multiple instances of e in accessQueue; remove them all
while (accessQueue.remove(e)) {
}
}
@Override
public void clear() {
accessQueue.clear();
}
@Override
public Eviction strategy() {
return Eviction.LIRS;
}
/**
* Returns the entry at the bottom of the stack.
*/
private LIRSHashEntry stackBottom() {
LIRSHashEntry bottom = header.previousInStack;
return (bottom == header) ? null : bottom;
}
/**
* Returns the entry at the front of the queue.
*/
private LIRSHashEntry queueFront() {
LIRSHashEntry front = header.nextInQueue;
return (front == header) ? null : front;
}
/**
* Returns the entry at the end of the queue.
*/
private LIRSHashEntry queueEnd() {
LIRSHashEntry end = header.previousInQueue;
return (end == header) ? null : end;
}
@Override
public HashEntry createNewEntry(K key, int hash, HashEntry next, V value) {
return new LIRSHashEntry(this,key, hash, next, value);
}
}
/**
* 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 = 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 (int)(capacity *
* loadFactor).)
*/
transient 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.
* @serial
*/
final float loadFactor;
final int evictCap;
transient final EvictionPolicy eviction;
transient final EvictionListener evictionListener;
Segment(int cap, int evictCap, float lf, Eviction es, EvictionListener listener) {
loadFactor = lf;
this.evictCap = evictCap;
eviction = es.make(this, evictCap, lf);
evictionListener = listener;
setTable(HashEntry. newArray(cap));
}
@SuppressWarnings("unchecked")
static Segment[] newArray(int i) {
return new Segment[i];
}
EvictionListener getEvictionListener() {
return evictionListener;
}
/**
* 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;
}
/**
* Returns properly casted first entry of bin for given hash.
*/
HashEntry getFirst(int hash) {
HashEntry[] 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 e) {
lock();
try {
return e.value;
} finally {
unlock();
}
}
/* Specialized implementations of map methods */
V get(Object key, int hash) {
int c = count;
if (c != 0) { // read-volatile
V result = null;
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && key.equals(e.key)) {
V v = e.value;
if (v != null) {
result = v;
break;
} else {
result = readValueUnderLock(e); // recheck
break;
}
}
e = e.next;
}
// a hit
if (result != null) {
if (eviction.onEntryHit(e)) {
Set> evicted = attemptEviction(false);
notifyEvictionListener(evicted);
}
}
return result;
}
return null;
}
boolean containsKey(Object key, int hash) {
if (count != 0) { // read-volatile
HashEntry e = getFirst(hash);
while (e != null) {
if (e.hash == hash && key.equals(e.key)) {
return true;
}
e = e.next;
}
}
return false;
}
boolean containsValue(Object value) {
if (count != 0) { // read-volatile
HashEntry[] tab = table;
int len = tab.length;
for (int i = 0 ; i < len; i++) {
for (HashEntry e = tab[i]; e != null; e = e.next) {
V v = e.value;
if (v == null) {
v = readValueUnderLock(e);
}
if (value.equals(v)) {
return true;
}
}
}
}
return false;
}
boolean replace(K key, int hash, V oldValue, V newValue) {
lock();
Set> evicted = null;
try {
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !key.equals(e.key))) {
e = e.next;
}
boolean replaced = false;
if (e != null && oldValue.equals(e.value)) {
replaced = true;
e.value = newValue;
if (eviction.onEntryHit(e)) {
evicted = attemptEviction(true);
}
}
return replaced;
} finally {
unlock();
notifyEvictionListener(evicted);
}
}
V replace(K key, int hash, V newValue) {
lock();
Set> evicted = null;
try {
HashEntry e = getFirst(hash);
while (e != null && (e.hash != hash || !key.equals(e.key))) {
e = e.next;
}
V oldValue = null;
if (e != null) {
oldValue = e.value;
e.value = newValue;
if (eviction.onEntryHit(e)) {
evicted = attemptEviction(true);
}
}
return oldValue;
} finally {
unlock();
notifyEvictionListener(evicted);
}
}
V put(K key, int hash, V value, boolean onlyIfAbsent) {
lock();
Set> evicted = null;
try {
int c = count;
if (c++ > threshold && eviction.strategy() == Eviction.NONE) {
rehash();
}
HashEntry[] tab = table;
int index = hash & tab.length - 1;
HashEntry first = tab[index];
HashEntry e = first;
while (e != null && (e.hash != hash || !key.equals(e.key))) {
e = e.next;
}
V oldValue;
if (e != null) {
oldValue = e.value;
if (!onlyIfAbsent) {
e.value = value;
eviction.onEntryHit(e);
}
} else {
oldValue = null;
++modCount;
count = c; // write-volatile
if (eviction.strategy() != Eviction.NONE) {
if (c > evictCap) {
// remove entries;lower count
evicted = eviction.execute();
// re-read first
first = tab[index];
}
// add a new entry
tab[index] = eviction.createNewEntry(key, hash, first, value);
// notify a miss
Set> newlyEvicted = eviction.onEntryMiss(tab[index]);
if (!newlyEvicted.isEmpty()) {
if (evicted != null) {
evicted.addAll(newlyEvicted);
} else {
evicted = newlyEvicted;
}
}
} else {
tab[index] = eviction.createNewEntry(key, hash, first, value);
}
}
return oldValue;
} finally {
unlock();
notifyEvictionListener(evicted);
}
}
void rehash() {
HashEntry[] 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[] 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 e = oldTable[i];
if (e != null) {
HashEntry next = e.next;
int idx = e.hash & sizeMask;
// Single node on list
if (next == null) {
newTable[idx] = e;
} else {
// Reuse trailing consecutive sequence at same slot
HashEntry lastRun = e;
int lastIdx = idx;
for (HashEntry last = next;
last != null;
last = last.next) {
int k = last.hash & sizeMask;
if (k != lastIdx) {
lastIdx = k;
lastRun = last;
}
}
newTable[lastIdx] = lastRun;
// Clone all remaining nodes
for (HashEntry p = e; p != lastRun; p = p.next) {
int k = p.hash & sizeMask;
HashEntry n = newTable[k];
newTable[k] = eviction.createNewEntry(p.key, p.hash, n, p.value);
}
}
}
}
table = newTable;
}
/**
* Remove; match on key only if value null, else match both.
*/
V remove(Object key, int hash, Object value) {
lock();
try {
int c = count - 1;
HashEntry[] tab = table;
int index = hash & tab.length - 1;
HashEntry first = tab[index];
HashEntry e = first;
while (e != null && (e.hash != hash || !key.equals(e.key))) {
e = e.next;
}
V oldValue = null;
if (e != null) {
V v = e.value;
if (value == null || value.equals(v)) {
oldValue = v;
// All entries following removed node can stay
// in list, but all preceding ones need to be
// cloned.
++modCount;
// e was removed
eviction.onEntryRemove(e);
HashEntry newFirst = e.next;
for (HashEntry p = first; p != e; p = p.next) {
// TODO A remove operation makes the map behave like all the other keys in the bucket were just added???
// allow p to be GC-ed
eviction.onEntryRemove(p);
newFirst = eviction.createNewEntry(p.key, p.hash, newFirst, p.value);
// and notify eviction algorithm about new hash entries
eviction.onEntryMiss(newFirst);
}
tab[index] = newFirst;
count = c; // write-volatile
}
}
return oldValue;
} finally {
unlock();
}
}
void clear() {
if (count != 0) {
lock();
try {
HashEntry[] tab = table;
for (int i = 0; i < tab.length; i++) {
tab[i] = null;
}
++modCount;
eviction.clear();
count = 0; // write-volatile
} finally {
unlock();
}
}
}
private Set> attemptEviction(boolean lockedAlready) {
Set> evicted = null;
boolean obtainedLock = lockedAlready || tryLock();
if (!obtainedLock && eviction.thresholdExpired()) {
lock();
obtainedLock = true;
}
if (obtainedLock) {
try {
if (eviction.thresholdExpired()) {
evicted = eviction.execute();
}
} finally {
if (!lockedAlready) {
unlock();
}
}
}
return evicted;
}
private void notifyEvictionListener(Set> evicted) {
// piggyback listener invocation on callers thread outside lock
if (evicted != null) {
Map evictedCopy;
if (evicted.size() == 1) {
HashEntry evictedEntry = evicted.iterator().next();
evictedCopy = singletonMap(evictedEntry.key, evictedEntry.value);
} else {
evictedCopy = new HashMap(evicted.size());
for (HashEntry he : evicted) {
evictedCopy.put(he.key, he.value);
}
evictedCopy = unmodifiableMap(evictedCopy);
}
evictionListener.onEntryEviction(evictedCopy);
}
}
}
/* ---------------- Public operations -------------- */
/**
* Creates a new, empty map with the specified maximum capacity, load factor and concurrency
* level.
*
* @param capacity
* is the upper bound capacity for the number of elements in this map
*
* @param concurrencyLevel
* the estimated number of concurrently updating threads. The implementation performs
* internal sizing to try to accommodate this many threads.
*
* @param evictionStrategy
* the algorithm used to evict elements from this map
*
* @param evictionListener
* the evicton listener callback to be notified about evicted elements
*
* @throws IllegalArgumentException
* if the initial capacity is negative or the load factor or concurrencyLevel are
* nonpositive.
*/
public BoundedConcurrentHashMap(int capacity, int concurrencyLevel,
Eviction evictionStrategy, EvictionListener evictionListener) {
if (capacity < 0 || concurrencyLevel <= 0) {
throw new IllegalArgumentException();
}
concurrencyLevel = Math.min(capacity / 2, concurrencyLevel); // concurrencyLevel cannot be > capacity/2
concurrencyLevel = Math.max(concurrencyLevel, 1); // concurrencyLevel cannot be less than 1
// minimum two elements per segment
if (capacity < concurrencyLevel * 2 && capacity != 1) {
throw new IllegalArgumentException("Maximum capacity has to be at least twice the concurrencyLevel");
}
if (evictionStrategy == null || evictionListener == null) {
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 (capacity > MAXIMUM_CAPACITY) {
capacity = MAXIMUM_CAPACITY;
}
int c = capacity / ssize;
int cap = 1;
while (cap < c) {
cap <<= 1;
}
for (int i = 0; i < this.segments.length; ++i) {
this.segments[i] = new Segment(cap, c, DEFAULT_LOAD_FACTOR, evictionStrategy, evictionListener);
}
}
/**
* Creates a new, empty map with the specified maximum capacity, load factor, concurrency
* level and LRU eviction policy.
*
* @param capacity
* is the upper bound capacity for the number of elements in this map
*
* @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 BoundedConcurrentHashMap(int capacity, int concurrencyLevel) {
this(capacity, concurrencyLevel, Eviction.LRU);
}
/**
* Creates a new, empty map with the specified maximum capacity, load factor, concurrency
* level and eviction strategy.
*
* @param capacity
* is the upper bound capacity for the number of elements in this map
*
* @param concurrencyLevel
* the estimated number of concurrently updating threads. The implementation performs
* internal sizing to try to accommodate this many threads.
*
* @param evictionStrategy
* the algorithm used to evict elements from this map
*
* @throws IllegalArgumentException
* if the initial capacity is negative or the load factor or concurrencyLevel are
* nonpositive.
*/
public BoundedConcurrentHashMap(int capacity, int concurrencyLevel, Eviction evictionStrategy) {
this(capacity, concurrencyLevel, evictionStrategy, new NullEvictionListener());
}
/**
* Creates a new, empty map with the specified maximum capacity, default concurrency
* level and LRU eviction policy.
*
* @param capacity
* is the upper bound capacity for the number of elements in this map
*
*
* @throws IllegalArgumentException if the initial capacity of
* elements is negative or the load factor is nonpositive
*
* @since 1.6
*/
public BoundedConcurrentHashMap(int capacity) {
this(capacity, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Creates a new, empty map with the default maximum capacity
*/
public BoundedConcurrentHashMap() {
this(DEFAULT_MAXIMUM_CAPACITY, DEFAULT_CONCURRENCY_LEVEL);
}
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings
*/
@Override
public boolean isEmpty() {
final Segment[] segments = this.segments;
/*
* We keep track of per-segment modCounts to avoid ABA
* problems in which an element in one segment was added and
* in another removed during traversal, in which case the
* table was never actually empty at any point. Note the
* similar use of modCounts in the size() and containsValue()
* methods, which are the only other methods also susceptible
* to ABA problems.
*/
int[] mc = new int[segments.length];
int mcsum = 0;
for (int i = 0; i < segments.length; ++i) {
if (segments[i].count != 0) {
return false;
} else {
mcsum += mc[i] = segments[i].modCount;
}
}
// If mcsum happens to be zero, then we know we got a snapshot
// before any modifications at all were made. This is
// probably common enough to bother tracking.
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++i) {
if (segments[i].count != 0 || mc[i] != segments[i].modCount) {
return false;
}
}
}
return true;
}
/**
* Returns the number of key-value mappings in this map. If the
* map contains more than Integer.MAX_VALUE elements, returns
* Integer.MAX_VALUE.
*
* @return the number of key-value mappings in this map
*/
@Override
public int size() {
final Segment[] segments = this.segments;
long sum = 0;
long check = 0;
int[] mc = new int[segments.length];
// Try a few times to get accurate count. On failure due to
// continuous async changes in table, resort to locking.
for (int k = 0; k < RETRIES_BEFORE_LOCK; ++ k) {
check = 0;
sum = 0;
int mcsum = 0;
for (int i = 0; i < segments.length; ++ i) {
sum += segments[i].count;
mcsum += mc[i] = segments[i].modCount;
}
if (mcsum != 0) {
for (int i = 0; i < segments.length; ++ i) {
check += segments[i].count;
if (mc[i] != segments[i].modCount) {
check = -1; // force retry
break;
}
}
}
if (check == sum) {
break;
}
}
if (check != sum) { // Resort to locking all segments
sum = 0;
for (int i = 0; i < segments.length; ++ i) {
segments[i].lock();
}
try {
for (int i = 0; i < segments.length; ++ i) {
sum += segments[i].count;
}
} finally {
for (int i = 0; i < segments.length; ++ i) {
segments[i].unlock();
}
}
}
if (sum > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
} else {
return (int) sum;
}
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* More formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code key.equals(k)},
* then this method returns {@code v}; otherwise it returns
* {@code null}. (There can be at most one such mapping.)
*
* @throws NullPointerException if the specified key is null
*/
@Override
public V get(Object key) {
int hash = hash(key.hashCode());
return segmentFor(hash).get(key, hash);
}
/**
* Tests if the specified object is a key in this table.
*
* @param key possible key
* @return 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 = hash(key.hashCode());
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) {
@SuppressWarnings("unused")
int c = segments[i].count; // read-volatile
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) {
@SuppressWarnings("unused")
int c = segments[i].count; // read-volatile
if (mc[i] != segments[i].modCount) {
cleanSweep = false;
break;
}
}
}
if (cleanSweep) {
return false;
}
}
// Resort to locking all segments
for (int i = 0; i < segments.length; ++ i) {
segments[i].lock();
}
boolean found = false;
try {
for (int i = 0; i < segments.length; ++ i) {
if (segments[i].containsValue(value)) {
found = true;
break;
}
}
} finally {
for (int i = 0; i < segments.length; ++ i) {
segments[i].unlock();
}
}
return found;
}
/**
* Legacy method testing if some key maps into the specified value
* in this table. This method is identical in functionality to
* {@link #containsValue}, and exists solely to ensure
* full compatibility with class {@link Hashtable},
* which supported this method prior to introduction of the
* Java Collections framework.
* @param value a value to search for
* @return true if and only if some key maps to the
* value argument in this table as
* determined by the equals method;
* false otherwise
* @throws NullPointerException if the specified value is null
*/
public boolean contains(Object value) {
return containsValue(value);
}
/**
* Maps the specified key to the specified value in this table.
* Neither the key nor the value can be null.
*
* The value can be retrieved by calling the get method
* with a key that is equal to the original key.
*
* @param key key with which the specified value is to be associated
* @param value value to be associated with the specified key
* @return the previous value associated with key, or
* null if there was no mapping for key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V put(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
int hash = hash(key.hashCode());
return segmentFor(hash).put(key, hash, value, false);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key,
* or null if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V putIfAbsent(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
int hash = hash(key.hashCode());
return segmentFor(hash).put(key, hash, value, true);
}
/**
* Copies all of the mappings from the specified map to this one.
* These mappings replace any mappings that this map had for any of the
* keys currently in the specified map.
*
* @param m mappings to be stored in this map
*/
@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 = hash(key.hashCode());
return segmentFor(hash).remove(key, hash, null);
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if the specified key is null
*/
@Override
public boolean remove(Object key, Object value) {
int hash = hash(key.hashCode());
if (value == null) {
return false;
}
return segmentFor(hash).remove(key, hash, value) != null;
}
/**
* {@inheritDoc}
*
* @throws NullPointerException if any of the arguments are null
*/
@Override
public boolean replace(K key, V oldValue, V newValue) {
if (oldValue == null || newValue == null) {
throw new NullPointerException();
}
int hash = hash(key.hashCode());
return segmentFor(hash).replace(key, hash, oldValue, newValue);
}
/**
* {@inheritDoc}
*
* @return the previous value associated with the specified key,
* or null if there was no mapping for the key
* @throws NullPointerException if the specified key or value is null
*/
@Override
public V replace(K key, V value) {
if (value == null) {
throw new NullPointerException();
}
int hash = hash(key.hashCode());
return segmentFor(hash).replace(key, hash, value);
}
/**
* Removes all of the mappings from this map.
*/
@Override
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 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;
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 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 nextEntry() {
if (nextEntry == null) {
throw new NoSuchElementException();
}
lastReturned = nextEntry;
advance();
return lastReturned;
}
public void remove() {
if (lastReturned == null) {
throw new IllegalStateException();
}
BoundedConcurrentHashMap.this.remove(lastReturned.key);
lastReturned = null;
}
}
final class KeyIterator extends HashIterator implements Iterator, Enumeration {
@Override
public K next() {
return super.nextEntry().key;
}
@Override
public K nextElement() {
return super.nextEntry().key;
}
}
final class ValueIterator extends HashIterator implements Iterator, Enumeration {
@Override
public V next() {
return super.nextEntry().value;
}
@Override
public V nextElement() {
return super.nextEntry().value;
}
}
/**
* Custom Entry class used by EntryIterator.next(), that relays
* setValue changes to the underlying map.
*/
final class WriteThroughEntry extends AbstractMap.SimpleEntry {
private static final long serialVersionUID = -7041346694785573824L;
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.
*/
@Override
public V setValue(V value) {
if (value == null) {
throw new NullPointerException();
}
V v = super.setValue(value);
BoundedConcurrentHashMap.this.put(getKey(), value);
return v;
}
}
final class EntryIterator extends HashIterator implements Iterator> {
@Override
public Map.Entry next() {
HashEntry e = super.nextEntry();
return new WriteThroughEntry(e.key, e.value);
}
}
final class KeySet extends AbstractSet {
@Override
public Iterator iterator() {
return new KeyIterator();
}
@Override
public int size() {
return BoundedConcurrentHashMap.this.size();
}
@Override
public boolean isEmpty() {
return BoundedConcurrentHashMap.this.isEmpty();
}
@Override
public boolean contains(Object o) {
return BoundedConcurrentHashMap.this.containsKey(o);
}
@Override
public boolean remove(Object o) {
return BoundedConcurrentHashMap.this.remove(o) != null;
}
@Override
public void clear() {
BoundedConcurrentHashMap.this.clear();
}
}
final class Values extends AbstractCollection {
@Override
public Iterator iterator() {
return new ValueIterator();
}
@Override
public int size() {
return BoundedConcurrentHashMap.this.size();
}
@Override
public boolean isEmpty() {
return BoundedConcurrentHashMap.this.isEmpty();
}
@Override
public boolean contains(Object o) {
return BoundedConcurrentHashMap.this.containsValue(o);
}
@Override
public void clear() {
BoundedConcurrentHashMap.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 = BoundedConcurrentHashMap.this.get(e.getKey());
return v != null && v.equals(e.getValue());
}
@Override
public boolean remove(Object o) {
if (!(o instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry) o;
return BoundedConcurrentHashMap.this.remove(e.getKey(), e.getValue());
}
@Override
public int size() {
return BoundedConcurrentHashMap.this.size();
}
@Override
public boolean isEmpty() {
return BoundedConcurrentHashMap.this.isEmpty();
}
@Override
public void clear() {
BoundedConcurrentHashMap.this.clear();
}
}
/* ---------------- Serialization Support -------------- */
/**
* Save the state of the ConcurrentHashMap 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 seg = segments[k];
seg.lock();
try {
HashEntry[] tab = seg.table;
for (int i = 0; i < tab.length; ++ i) {
for (HashEntry 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 ConcurrentHashMap 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);
}
}
}