程序包 cn.taketoday.util

类 ConcurrentReferenceHashMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

cn.taketoday.util.ConcurrentReferenceHashMap<K,V>

类型参数:

K - the key type

V - the value type

所有已实现的接口:

ConcurrentMap<K,V>, Map<K,V>

public class ConcurrentReferenceHashMap<K,V>
extends AbstractMap<K,V>
implements ConcurrentMap<K,V>

A ConcurrentHashMap that uses soft or weak references for both keys and values.

This class can be used as an alternative to Collections.synchronizedMap(new WeakHashMap<K, Reference<V>>()) in order to support better performance when accessed concurrently. This implementation follows the same design constraints as ConcurrentHashMap with the exception that null values and null keys are supported.

NOTE: The use of references means that there is no guarantee that items placed into the map will be subsequently available. The garbage collector may discard references at any time, so it may appear that an unknown thread is silently removing entries.

If not explicitly specified, this implementation will use soft entry references.

从以下版本开始:

4.0

作者:

Phillip Webb, Juergen Hoeller, TODAY 2021/9/11 12:49

嵌套类概要

嵌套类

修饰符和类型	类	说明
private static interface	ConcurrentReferenceHashMap.Entries<V>	Allows a task access to ConcurrentReferenceHashMap.Segment entries.
protected static final class	ConcurrentReferenceHashMap.Entry<K,V>	A single map entry.
private class	ConcurrentReferenceHashMap.EntryIterator	Internal entry iterator implementation.
private class	ConcurrentReferenceHashMap.EntrySet	Internal entry-set implementation.
protected static interface	ConcurrentReferenceHashMap.Reference<K,V>	A reference to an ConcurrentReferenceHashMap.Entry contained in the map.
protected class	ConcurrentReferenceHashMap.ReferenceManager	Strategy class used to manage References.
static enum	ConcurrentReferenceHashMap.ReferenceType	Various reference types supported by this map.
protected static enum	ConcurrentReferenceHashMap.Restructure	The types of restructuring that can be performed.
protected final class	ConcurrentReferenceHashMap.Segment	A single segment used to divide the map to allow better concurrent performance.
private static final class	ConcurrentReferenceHashMap.SoftEntryReference<K,V>	Internal ConcurrentReferenceHashMap.Reference implementation for SoftReferences.
private class	ConcurrentReferenceHashMap.Task<T>	A task that can be run against a ConcurrentReferenceHashMap<K,V>.Segment.
private static enum	ConcurrentReferenceHashMap.TaskOption	Various options supported by a Task.
private static final class	ConcurrentReferenceHashMap.WeakEntryReference<K,V>	Internal ConcurrentReferenceHashMap.Reference implementation for WeakReferences.

从类继承的嵌套类/接口 java.util.AbstractMap

AbstractMap.SimpleEntry<K extends Object,V extends Object>, AbstractMap.SimpleImmutableEntry<K extends Object,V extends Object>

字段概要

字段

修饰符和类型	字段	说明
private static final int	DEFAULT_CONCURRENCY_LEVEL
private static final int	DEFAULT_INITIAL_CAPACITY
private static final float	DEFAULT_LOAD_FACTOR
private static final ConcurrentReferenceHashMap.ReferenceType	DEFAULT_REFERENCE_TYPE
private Set<Map.Entry<K,V>>	entrySet	Late binding entry set.
private final float	loadFactor	When the average number of references per table exceeds this value resize will be attempted.
private static final int	MAXIMUM_CONCURRENCY_LEVEL
private static final int	MAXIMUM_SEGMENT_SIZE
private final ConcurrentReferenceHashMap.ReferenceType	referenceType	The reference type: SOFT or WEAK.
private final ConcurrentReferenceHashMap<K,V>.Segment[]	segments	Array of segments indexed using the high order bits from the hash.
private final int	shift	The shift value used to calculate the size of the segments array and an index from the hash.

构造器概要

构造器

构造器	说明
ConcurrentReferenceHashMap()	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity)	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity, float loadFactor)	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity, float loadFactor, int concurrencyLevel)	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity, float loadFactor, int concurrencyLevel, ConcurrentReferenceHashMap.ReferenceType referenceType)	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity, int concurrencyLevel)	Create a new ConcurrentReferenceHashMap instance.
ConcurrentReferenceHashMap(int initialCapacity, ConcurrentReferenceHashMap.ReferenceType referenceType)	Create a new ConcurrentReferenceHashMap instance.

方法概要

修饰符和类型	方法	说明
protected static int	calculateShift(int minimumValue, int maximumValue)	Calculate a shift value that can be used to create a power-of-two value between the specified maximum and minimum values.
void	clear()
boolean	containsKey(Object key)
private static ConcurrentReferenceHashMap.Reference[]	createReferenceArray(int size)
protected ConcurrentReferenceHashMap<K,V>.ReferenceManager	createReferenceManager()	Factory method that returns the ConcurrentReferenceHashMap<K,V>.ReferenceManager.
private <T> T	doTask(Object key, ConcurrentReferenceHashMap<K,V>.Task<T> task)
Set<Map.Entry<K,V>>	entrySet()
private static <K, V> ConcurrentReferenceHashMap.Reference<K,V>	findInChain(ConcurrentReferenceHashMap.Reference<K,V> ref, Object key, int hash)
private static ConcurrentReferenceHashMap.Reference	findInChain(Object key, int hash, ConcurrentReferenceHashMap.Reference[] references)
V	get(Object key)
protected int	getHash(Object o)	Get the hash for a given object, apply an additional hash function to reduce collisions.
private static int	getIndex(int hash, ConcurrentReferenceHashMap.Reference[] references)
protected final float	getLoadFactor()
V	getOrDefault(Object key, V defaultValue)
protected final ConcurrentReferenceHashMap.Reference<K,V>	getReference(Object key, ConcurrentReferenceHashMap.Restructure restructure)	Return a ConcurrentReferenceHashMap.Reference to the ConcurrentReferenceHashMap.Entry for the specified key, or null if not found.
protected final ConcurrentReferenceHashMap<K,V>.Segment	getSegment(int index)
private ConcurrentReferenceHashMap<K,V>.Segment	getSegmentForHash(int hash)
protected final int	getSegmentsSize()
boolean	isEmpty()
void	purgeUnreferencedEntries()	Remove any entries that have been garbage collected and are no longer referenced.
V	put(K key, V value)
private V	put(K key, V value, boolean overwriteExisting)
V	putIfAbsent(K key, V value)
V	remove(Object key)
boolean	remove(Object key, Object value)
V	replace(K key, V value)
boolean	replace(K key, V oldValue, V newValue)
int	size()

从类继承的方法 java.util.AbstractMap

clone, containsValue, equals, hashCode, keySet, putAll, toString, values

从类继承的方法 java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

从接口继承的方法 java.util.concurrent.ConcurrentMap

compute, computeIfAbsent, computeIfPresent, forEach, merge, replaceAll

从接口继承的方法 java.util.Map

containsValue, equals, hashCode, keySet, putAll, values

字段详细资料

DEFAULT_INITIAL_CAPACITY

private static final int DEFAULT_INITIAL_CAPACITY

另请参阅:

• 常量字段值

DEFAULT_LOAD_FACTOR

private static final float DEFAULT_LOAD_FACTOR

另请参阅:

• 常量字段值

DEFAULT_CONCURRENCY_LEVEL

private static final int DEFAULT_CONCURRENCY_LEVEL

另请参阅:

• 常量字段值

DEFAULT_REFERENCE_TYPE

private static final ConcurrentReferenceHashMap.ReferenceType DEFAULT_REFERENCE_TYPE

MAXIMUM_CONCURRENCY_LEVEL

private static final int MAXIMUM_CONCURRENCY_LEVEL

另请参阅:

• 常量字段值

MAXIMUM_SEGMENT_SIZE

private static final int MAXIMUM_SEGMENT_SIZE

另请参阅:

• 常量字段值

segments

private final ConcurrentReferenceHashMap<K,V>.Segment[] segments

Array of segments indexed using the high order bits from the hash.

loadFactor

private final float loadFactor

When the average number of references per table exceeds this value resize will be attempted.

referenceType

private final ConcurrentReferenceHashMap.ReferenceType referenceType

The reference type: SOFT or WEAK.

shift

private final int shift

The shift value used to calculate the size of the segments array and an index from the hash.

entrySet

@Nullable
private volatile Set<Map.Entry<K,V>> entrySet

Late binding entry set.

构造器详细资料

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap()

Create a new ConcurrentReferenceHashMap instance.

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity,
 float loadFactor)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

loadFactor - the load factor. When the average number of references per table exceeds this value resize will be attempted

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity,
 int concurrencyLevel)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

concurrencyLevel - the expected number of threads that will concurrently write to the map

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity,
 ConcurrentReferenceHashMap.ReferenceType referenceType)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

referenceType - the reference type used for entries (soft or weak)

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity,
 float loadFactor,
 int concurrencyLevel)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

loadFactor - the load factor. When the average number of references per table exceeds this value, resize will be attempted.

concurrencyLevel - the expected number of threads that will concurrently write to the map

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(int initialCapacity,
 float loadFactor,
 int concurrencyLevel,
 ConcurrentReferenceHashMap.ReferenceType referenceType)

Create a new ConcurrentReferenceHashMap instance.

参数:

initialCapacity - the initial capacity of the map

loadFactor - the load factor. When the average number of references per table exceeds this value, resize will be attempted.

concurrencyLevel - the expected number of threads that will concurrently write to the map

referenceType - the reference type used for entries (soft or weak)

方法详细资料

getLoadFactor

protected final float getLoadFactor()

getSegmentsSize

protected final int getSegmentsSize()

getSegment

protected final ConcurrentReferenceHashMap<K,V>.Segment getSegment(int index)

createReferenceManager

protected ConcurrentReferenceHashMap<K,V>.ReferenceManager createReferenceManager()

Factory method that returns the ConcurrentReferenceHashMap<K,V>.ReferenceManager. This method will be called once for each ConcurrentReferenceHashMap<K,V>.Segment.

返回:

a new reference manager

getHash

protected int getHash(@Nullable
 Object o)

Get the hash for a given object, apply an additional hash function to reduce collisions. This implementation uses the same Wang/Jenkins algorithm as ConcurrentHashMap. Subclasses can override to provide alternative hashing.

参数:

o - the object to hash (may be null)

返回:

the resulting hash code

get

@Nullable
public V get(@Nullable
 Object key)

指定者:

get 在接口中 Map<K,V>

覆盖:

get 在类中 AbstractMap<K,V>

getOrDefault

@Nullable
public V getOrDefault(@Nullable
 Object key,
 @Nullable
 V defaultValue)

指定者:

getOrDefault 在接口中 ConcurrentMap<K,V>

指定者:

getOrDefault 在接口中 Map<K,V>

containsKey

public boolean containsKey(@Nullable
 Object key)

指定者:

containsKey 在接口中 Map<K,V>

覆盖:

containsKey 在类中 AbstractMap<K,V>

getReference

@Nullable
protected final ConcurrentReferenceHashMap.Reference<K,V> getReference(@Nullable
 Object key,
 ConcurrentReferenceHashMap.Restructure restructure)

Return a ConcurrentReferenceHashMap.Reference to the ConcurrentReferenceHashMap.Entry for the specified key, or null if not found.

参数:

key - the key (can be null)

restructure - types of restructure allowed during this call

返回:

the reference, or null if not found

put

@Nullable
public V put(@Nullable
 K key,
 @Nullable
 V value)

指定者:

put 在接口中 Map<K,V>

覆盖:

put 在类中 AbstractMap<K,V>

putIfAbsent

@Nullable
public V putIfAbsent(@Nullable
 K key,
 @Nullable
 V value)

指定者:

putIfAbsent 在接口中 ConcurrentMap<K,V>

指定者:

putIfAbsent 在接口中 Map<K,V>

put

@Nullable
private V put(@Nullable
 K key,
 @Nullable
 V value,
 boolean overwriteExisting)

remove

@Nullable
public V remove(@Nullable
 Object key)

指定者:

remove 在接口中 Map<K,V>

覆盖:

remove 在类中 AbstractMap<K,V>

remove

public boolean remove(@Nullable
 Object key,
 @Nullable
 Object value)

指定者:

remove 在接口中 ConcurrentMap<K,V>

指定者:

remove 在接口中 Map<K,V>

replace

public boolean replace(@Nullable
 K key,
 @Nullable
 V oldValue,
 @Nullable
 V newValue)

指定者:

replace 在接口中 ConcurrentMap<K,V>

指定者:

replace 在接口中 Map<K,V>

replace

@Nullable
public V replace(@Nullable
 K key,
 @Nullable
 V value)

指定者:

replace 在接口中 ConcurrentMap<K,V>

指定者:

replace 在接口中 Map<K,V>

clear

public void clear()

指定者:

clear 在接口中 Map<K,V>

覆盖:

clear 在类中 AbstractMap<K,V>

purgeUnreferencedEntries

public void purgeUnreferencedEntries()

Remove any entries that have been garbage collected and are no longer referenced. Under normal circumstances garbage collected entries are automatically purged as items are added or removed from the Map. This method can be used to force a purge, and is useful when the Map is read frequently but updated less often.

size

public int size()

指定者:

size 在接口中 Map<K,V>

覆盖:

size 在类中 AbstractMap<K,V>

isEmpty

public boolean isEmpty()

指定者:

isEmpty 在接口中 Map<K,V>

覆盖:

isEmpty 在类中 AbstractMap<K,V>

entrySet

public Set<Map.Entry<K,V>> entrySet()

指定者:

entrySet 在接口中 Map<K,V>

指定者:

entrySet 在类中 AbstractMap<K,V>

doTask

@Nullable
private <T> T doTask(@Nullable
 Object key,
 ConcurrentReferenceHashMap<K,V>.Task<T> task)

getSegmentForHash

private ConcurrentReferenceHashMap<K,V>.Segment getSegmentForHash(int hash)

calculateShift

protected static int calculateShift(int minimumValue,
 int maximumValue)

Calculate a shift value that can be used to create a power-of-two value between the specified maximum and minimum values.

参数:

minimumValue - the minimum value

maximumValue - the maximum value

返回:

the calculated shift (use 1 << shift to obtain a value)

createReferenceArray

private static ConcurrentReferenceHashMap.Reference[] createReferenceArray(int size)

findInChain

@Nullable
private static ConcurrentReferenceHashMap.Reference findInChain(@Nullable
 Object key,
 int hash,
 ConcurrentReferenceHashMap.Reference[] references)

getIndex

private static int getIndex(int hash,
 ConcurrentReferenceHashMap.Reference[] references)

findInChain

@Nullable
private static <K,
V>
ConcurrentReferenceHashMap.Reference<K,V> findInChain(ConcurrentReferenceHashMap.Reference<K,V> ref,
 @Nullable
 Object key,
 int hash)