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/*
* 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 by Vladimir Blagojevic to include lock amortized eviction.
* For more details see http://www.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-09-1.pdf
* https://jira.jboss.org/jira/browse/ISPN-299
*
*/
package org.infinispan.util.concurrent;
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.LinkedList;
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;
/**
* 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 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.
*
*
* Like {@link Hashtable} but unlike {@link HashMap}, this class does not allow
* null to be used as a key or value.
*
*
* This class is a member of the
* Java Collections Framework.
*
* @since 1.5
* @author Doug Lea
* @param
* the type of keys maintained by this map
* @param
* the type of mapped values
*/
public class BufferedConcurrentHashMap 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_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[] 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.
*/
static final class HashEntry {
final K key;
final int hash;
volatile V value;
final HashEntry next;
volatile Recency state;
HashEntry(K key, int hash, HashEntry next, V value) {
this.key = key;
this.hash = hash;
this.next = next;
this.value = value;
this.state = Recency.HIR_RESIDENT;
}
public int hashCode() {
int result = 17;
result = (result * 31) + hash;
result = (result * 31) + key.hashCode();
return result;
}
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);
}
public void transitionHIRResidentToLIRResident() {
assert state == Recency.HIR_RESIDENT;
state = Recency.LIR_RESIDENT;
}
public void transitionHIRResidentToHIRNonResident() {
assert state == Recency.HIR_RESIDENT;
state = Recency.HIR_NONRESIDENT;
}
public void transitionHIRNonResidentToLIRResident() {
assert state == Recency.HIR_NONRESIDENT;
state = Recency.LIR_RESIDENT;
}
public void transitionLIRResidentToHIRResident() {
assert state == Recency.LIR_RESIDENT;
state = Recency.HIR_RESIDENT;
}
public Recency recency() {
return state;
}
@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,lf,capacity*10,lf);
}
};
abstract EvictionPolicy make(Segment s, int capacity, float lf);
}
public interface EvictionListener {
void evicted(K key, V value);
}
static class NullEvictionListener implements EvictionListener{
//@Override
public void evicted(K key, V value) {
}
}
interface EvictionPolicy {
public final static int MAX_BATCH_SIZE = 64;
/**
* 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
*/
void 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() {
}
//@Override
public Set> execute() {
return Collections.emptySet();
}
//@Override
public boolean onEntryHit(HashEntry e) {
return false;
}
//@Override
public void onEntryMiss(HashEntry e) {
}
//@Override
public void onEntryRemove(HashEntry e) {
}
//@Override
public boolean thresholdExpired() {
return false;
}
//@Override
public Eviction strategy() {
return Eviction.NONE;
}
}
static final class LRU implements EvictionPolicy {
private final ConcurrentLinkedQueue> accessQueue;
private final Segment segment;
private final LinkedList> lruQueue;
private final int maxBatchQueueSize;
private final int trimDownSize;
private final float batchThresholdFactor;
public LRU(Segment s, int capacity, float lf, int maxBatchSize, float batchThresholdFactor) {
this.segment = s;
this.trimDownSize = (int) (capacity * lf);
this.maxBatchQueueSize = maxBatchSize > MAX_BATCH_SIZE ? MAX_BATCH_SIZE : maxBatchSize;
this.batchThresholdFactor = batchThresholdFactor;
this.accessQueue = new ConcurrentLinkedQueue>();
this.lruQueue = new LinkedList>();
}
//@Override
public Set> execute() {
Set> evicted = Collections.emptySet();
if (isOverflow()) {
evicted = new HashSet>();
}
try {
for (HashEntry e : accessQueue) {
if (lruQueue.remove(e)) {
lruQueue.addFirst(e);
}
}
while (isOverflow()) {
HashEntry first = lruQueue.getLast();
segment.remove(first.key, first.hash, null);
evicted.add(first);
}
} finally {
accessQueue.clear();
}
return evicted;
}
private boolean isOverflow() {
return lruQueue.size() > trimDownSize;
}
//@Override
public void onEntryMiss(HashEntry e) {
lruQueue.addFirst(e);
}
/*
* 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) {
assert lruQueue.remove(e);
// we could have multiple instances of e in accessQueue; remove them all
while (accessQueue.remove(e))
;
}
//@Override
public void clear() {
lruQueue.clear();
accessQueue.clear();
}
//@Override
public Eviction strategy() {
return Eviction.LRU;
}
}
static final class LIRS implements EvictionPolicy {
private final static int MIN_HIR_SIZE = 2;
private final Segment segment;
private final ConcurrentLinkedQueue> accessQueue;
private final LinkedHashMap> stack;
private final LinkedList> queue;
private final int maxBatchQueueSize;
private final int lirSizeLimit;
private final int hirSizeLimit;
private int currentLIRSize;
private final float batchThresholdFactor;
public LIRS(Segment s, int capacity, float lf, int maxBatchSize, float batchThresholdFactor) {
this.segment = s;
int tmpLirSize = (int) (capacity * 0.9);
int tmpHirSizeLimit = capacity - tmpLirSize;
if (tmpHirSizeLimit < MIN_HIR_SIZE) {
hirSizeLimit = MIN_HIR_SIZE;
lirSizeLimit = capacity - hirSizeLimit;
} else {
hirSizeLimit = tmpHirSizeLimit;
lirSizeLimit = tmpLirSize;
}
this.maxBatchQueueSize = maxBatchSize > MAX_BATCH_SIZE ? MAX_BATCH_SIZE : maxBatchSize;
this.batchThresholdFactor = batchThresholdFactor;
this.accessQueue = new ConcurrentLinkedQueue>();
this.stack = new LinkedHashMap>();
this.queue = new LinkedList>();
}
//@Override
public Set> execute() {
Set> evicted = new HashSet>();
try {
for (HashEntry e : accessQueue) {
if (present(e)) {
if (e.recency() == Recency.LIR_RESIDENT) {
handleLIRHit(e, evicted);
} else if (e.recency() == Recency.HIR_RESIDENT) {
handleHIRHit(e, evicted);
}
}
}
removeFromSegment(evicted);
} finally {
accessQueue.clear();
}
return evicted;
}
private void handleHIRHit(HashEntry e, Set> evicted) {
boolean inStack = stack.containsKey(e.hashCode());
if (inStack)
stack.remove(e.hashCode());
// first put on top of the stack
stack.put(e.hashCode(), e);
if (inStack) {
assert queue.contains(e);
queue.remove(e);
e.transitionHIRResidentToLIRResident();
switchBottomostLIRtoHIRAndPrune(evicted);
} else {
assert queue.contains(e);
queue.remove(e);
queue.addLast(e);
}
}
private void handleLIRHit(HashEntry e, Set> evicted) {
stack.remove(e.hashCode());
stack.put(e.hashCode(), e);
for (Iterator> i = stack.values().iterator(); i.hasNext();) {
HashEntry next = i.next();
if (next.recency() == Recency.LIR_RESIDENT) {
break;
} else {
i.remove();
evicted.add(next);
}
}
}
private boolean present(HashEntry e) {
return stack.containsKey(e.hashCode()) || queue.contains(e);
}
//@Override
public void onEntryMiss(HashEntry e) {
// initialization
if (currentLIRSize + 1 < lirSizeLimit) {
currentLIRSize++;
e.transitionHIRResidentToLIRResident();
stack.put(e.hashCode(), e);
} else {
if (queue.size() < hirSizeLimit) {
assert !queue.contains(e);
queue.addLast(e);
} else {
boolean inStack = stack.containsKey(e.hashCode());
HashEntry first = queue.removeFirst();
assert first.recency() == Recency.HIR_RESIDENT;
first.transitionHIRResidentToHIRNonResident();
stack.put(e.hashCode(), e);
if (inStack) {
e.transitionHIRResidentToLIRResident();
Set> evicted = new HashSet>();
switchBottomostLIRtoHIRAndPrune(evicted);
removeFromSegment(evicted);
} else {
assert !queue.contains(e);
queue.addLast(e);
}
// evict from segment
segment.remove(first.key, first.hash, null);
}
}
}
private void removeFromSegment(Set> evicted) {
for (HashEntry e : evicted) {
segment.remove(e.key, e.hash, null);
}
}
private void switchBottomostLIRtoHIRAndPrune(Set> evicted) {
boolean seenFirstLIR = false;
for (Iterator> i = stack.values().iterator(); i.hasNext();) {
HashEntry next = i.next();
if (next.recency() == Recency.LIR_RESIDENT) {
if (!seenFirstLIR) {
seenFirstLIR = true;
i.remove();
next.transitionLIRResidentToHIRResident();
assert !queue.contains(next);
queue.addLast(next);
} else {
break;
}
} else {
i.remove();
evicted.add(next);
}
}
}
/*
* 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) {
HashEntry removed = stack.remove(e.hashCode());
if (removed != null && removed.recency() == Recency.LIR_RESIDENT) {
currentLIRSize--;
}
queue.remove(e);
// we could have multiple instances of e in accessQueue; remove them all
while (accessQueue.remove(e));
}
//@Override
public void clear() {
stack.clear();
accessQueue.clear();
}
//@Override
public Eviction strategy() {
return Eviction.LIRS;
}
}
/**
* 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 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 (int)(capacity *
* loadFactor).)
*/
transient int threshold;
/**
* The per-segment table.
*/
transient volatile HashEntry[] table;
transient final EvictionPolicy eviction;
transient final EvictionListener evictionListener;
/**
* 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 cap, float lf, Eviction es, EvictionListener listener) {
loadFactor = lf;
eviction = es.make(this, cap, lf);
evictionListener = listener;
setTable(HashEntry. newArray(cap));
}
@SuppressWarnings("unchecked")
static Segment[] newArray(int i) {
return new Segment[i];
}
/**
* 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();
}
}
V get(Object key, int hash) {
int c = count;
if (c != 0) { // read-volatile
V result = null;
HashEntry e = getFirst(hash);
loop: while (e != null) {
if (e.hash == hash && key.equals(e.key)) {
V v = e.value;
if (v != null) {
result = v;
break loop;
} else {
result = readValueUnderLock(e); // recheck
break loop;
}
}
e = e.next;
}
// a hit
if (result != null) {
if (eviction.onEntryHit(e)) {
Set> evicted = attemptEviction(false);
// piggyback listener invocation on callers thread outside lock
if (evicted != null) {
for (HashEntry he : evicted) {
evictionListener.evicted(he.key, he.value);
}
}
}
}
return result;
}
return null;
}
private Set> attemptEviction(boolean lockedAlready) {
Set> evicted = null;
boolean obtainedLock = !lockedAlready ? tryLock() : true;
if (!obtainedLock && eviction.thresholdExpired()) {
lock();
obtainedLock = true;
}
if (obtainedLock) {
try {
evicted = eviction.execute();
} finally {
if (!lockedAlready)
unlock();
}
}
return evicted;
}
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) // recheck
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();
// piggyback listener invocation on callers thread outside lock
if (evicted != null) {
for (HashEntry he : evicted) {
evictionListener.evicted(he.key, he.value);
}
}
}
}
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();
// piggyback listener invocation on callers thread outside lock
if(evicted != null) {
for (HashEntry he : evicted) {
evictionListener.evicted(he.key, he.value);
}
}
}
}
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) // ensure capacity
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 > tab.length) {
// remove entries;lower count
evicted = eviction.execute();
// re-read first
first = tab[index];
}
// add a new entry
tab[index] = new HashEntry(key, hash, first, value);
// notify a miss
eviction.onEntryMiss(tab[index]);
} else {
tab[index] = new HashEntry(key, hash, first, value);
}
}
return oldValue;
} finally {
unlock();
// piggyback listener invocation on callers thread outside lock
if(evicted != null) {
for (HashEntry he : evicted) {
evictionListener.evicted(he.key, he.value);
}
}
}
}
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] = new HashEntry(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) {
// allow p to be GC-ed
eviction.onEntryRemove(p);
newFirst = new HashEntry(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();
}
}
}
}
/* ---------------- 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.
*
* @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 BufferedConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel,
Eviction evictionStrategy, EvictionListener evictionListener) {
if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
throw new IllegalArgumentException();
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 (initialCapacity > MAXIMUM_CAPACITY)
initialCapacity = MAXIMUM_CAPACITY;
int c = initialCapacity / ssize;
if (c * ssize < initialCapacity)
++c;
int cap = 1;
while (cap < c)
cap <<= 1;
for (int i = 0; i < this.segments.length; ++i)
this.segments[i] = new Segment(cap, loadFactor, evictionStrategy,
evictionListener);
}
public BufferedConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel) {
this(initialCapacity, loadFactor, concurrencyLevel, Eviction.LRU);
}
public BufferedConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel, Eviction evictionStrategy) {
this(initialCapacity, loadFactor, concurrencyLevel, evictionStrategy, new NullEvictionListener());
}
/**
* 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 1.6
*/
public BufferedConcurrentHashMap(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 BufferedConcurrentHashMap(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 BufferedConcurrentHashMap() {
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 BufferedConcurrentHashMap(Map m) {
this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY),
DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
putAll(m);
}
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings
*/
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
*/
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 (true) { // Resort to locking all segments
sum = 0;
for (int i = 0; i < segments.length; ++i)
segments[i].lock();
for (int i = 0; i < segments.length; ++i)
sum += segments[i].count;
for (int i = 0; i < segments.length; ++i)
segments[i].unlock();
}
if (sum > Integer.MAX_VALUE)
return Integer.MAX_VALUE;
else
return (int) sum;
}
/**
* Returns the value to which the specified key is mapped, or {@code null} if this map contains
* no mapping for the key.
*
*
* More formally, if this map contains a mapping from a key {@code k} to a value {@code v} such
* that {@code key.equals(k)}, then this method returns {@code v}; otherwise it returns {@code
* null}. (There can be at most one such mapping.)
*
* @throws NullPointerException
* if the specified key is null
*/
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
*/
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
*/
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 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 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
*/
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
*/
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
*/
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
*/
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
*/
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
*/
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
*/
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.
*/
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.
*/
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.
*/
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.
*/
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();
BufferedConcurrentHashMap.this.remove(lastReturned.key);
lastReturned = null;
}
}
final class KeyIterator extends HashIterator implements Iterator, Enumeration {
public K next() {
return super.nextEntry().key;
}
public K nextElement() {
return super.nextEntry().key;
}
}
final class ValueIterator extends HashIterator implements Iterator, Enumeration {
public V next() {
return super.nextEntry().value;
}
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 = -1075078642155041669L;
WriteThroughEntry(K k, V v) {
super(k, v);
}
/**
* Set our entry's value and write through to the map. The value to return is somewhat
* arbitrary here. Since a WriteThroughEntry does not necessarily track asynchronous
* changes, the most recent "previous" value could be different from what we return (or
* could even have been removed in which case the put will re-establish). We do not and
* cannot guarantee more.
*/
public V setValue(V value) {
if (value == null)
throw new NullPointerException();
V v = super.setValue(value);
BufferedConcurrentHashMap.this.put(getKey(), value);
return v;
}
}
final class EntryIterator extends HashIterator implements Iterator> {
public Map.Entry next() {
HashEntry e = super.nextEntry();
return new WriteThroughEntry(e.key, e.value);
}
}
final class KeySet extends AbstractSet {
public Iterator iterator() {
return new KeyIterator();
}
public int size() {
return BufferedConcurrentHashMap.this.size();
}
public boolean contains(Object o) {
return BufferedConcurrentHashMap.this.containsKey(o);
}
public boolean remove(Object o) {
return BufferedConcurrentHashMap.this.remove(o) != null;
}
public void clear() {
BufferedConcurrentHashMap.this.clear();
}
}
final class Values extends AbstractCollection {
public Iterator iterator() {
return new ValueIterator();
}
public int size() {
return BufferedConcurrentHashMap.this.size();
}
public boolean contains(Object o) {
return BufferedConcurrentHashMap.this.containsValue(o);
}
public void clear() {
BufferedConcurrentHashMap.this.clear();
}
}
final class EntrySet extends AbstractSet> {
public Iterator> iterator() {
return new EntryIterator();
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry) o;
V v = BufferedConcurrentHashMap.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 BufferedConcurrentHashMap.this.remove(e.getKey(), e.getValue());
}
public int size() {
return BufferedConcurrentHashMap.this.size();
}
public void clear() {
BufferedConcurrentHashMap.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
*/
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);
}
}
}