Package io.micronaut.core.util.clhm

Class ConcurrentLinkedHashMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

io.micronaut.core.util.clhm.ConcurrentLinkedHashMap<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Implemented Interfaces:

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

public final class ConcurrentLinkedHashMap<K,V>
extends AbstractMap<K,V>
implements ConcurrentMap<K,V>, Serializable

A hash table supporting full concurrency of retrievals, adjustable expected concurrency for updates, and a maximum capacity to bound the map by. This implementation differs from ConcurrentHashMap in that it maintains a page replacement algorithm that is used to evict an entry when the map has exceeded its capacity. Unlike the Java Collections Framework, this map does not have a publicly visible constructor and instances are created through a ConcurrentLinkedHashMap.Builder.

An entry is evicted from the map when the weighted capacity exceeds its maximum weighted capacity threshold. A EntryWeigher determines how many units of capacity that an entry consumes. The default weigher assigns each value a weight of 1 to bound the map by the total number of key-value pairs. A map that holds collections may choose to weigh values by the number of elements in the collection and bound the map by the total number of elements that it contains. A change to a value that modifies its weight requires that an update operation is performed on the map.

An EvictionListener may be supplied for notification when an entry is evicted from the map. This listener is invoked on a caller's thread and will not block other threads from operating on the map. An implementation should be aware that the caller's thread will not expect long execution times or failures as a side effect of the listener being notified. Execution safety and a fast turn around time can be achieved by performing the operation asynchronously, such as by submitting a task to an ExecutorService.

The concurrency level determines the number of threads that can concurrently modify the table. Using a significantly higher or lower value than needed can waste space or lead to thread contention, but an estimate within an order of magnitude of the ideal value does not usually have a noticeable impact. Because placement in hash tables is essentially random, the actual concurrency will vary.

This class and its views and iterators implement all of the optional methods of the Map and Iterator interfaces.

Like Hashtable but unlike HashMap, this class does not allow null to be used as a key or value. Unlike LinkedHashMap, this class does not provide predictable iteration order. A snapshot of the keys and entries may be obtained in ascending and descending order of retention.

Author:

ben.manes@gmail.com (Ben Manes)

See Also:

• https://code.google.com/p/concurrentlinkedhashmap/
• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	ConcurrentLinkedHashMap.Builder<K,V>	A builder that creates ConcurrentLinkedHashMap instances.

Nested classes/interfaces inherited from class java.util.AbstractMap

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

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K extends Object,V extends Object>

Method Summary

Modifier and Type	Method	Description
Set<K>	ascendingKeySet()	Returns a unmodifiable snapshot Set view of the keys contained in this map.
Set<K>	ascendingKeySetWithLimit(int limit)	Returns an unmodifiable snapshot Set view of the keys contained in this map.
Map<K,V>	ascendingMap()	Returns an unmodifiable snapshot Map view of the mappings contained in this map.
Map<K,V>	ascendingMapWithLimit(int limit)	Returns an unmodifiable snapshot Map view of the mappings contained in this map.
long	capacity()	Retrieves the maximum weighted capacity of the map.
void	clear()
V	computeIfAbsent(K key, Function<? super K,? extends V> mappingFunction)	If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless null.
boolean	containsKey(Object key)
boolean	containsValue(Object value)
Set<K>	descendingKeySet()	Returns an unmodifiable snapshot Set view of the keys contained in this map.
Set<K>	descendingKeySetWithLimit(int limit)	Returns an unmodifiable snapshot Set view of the keys contained in this map.
Map<K,V>	descendingMap()	Returns an unmodifiable snapshot Map view of the mappings contained in this map.
Map<K,V>	descendingMapWithLimit(int limit)	Returns an unmodifiable snapshot Map view of the mappings contained in this map.
Set<Map.Entry<K,V>>	entrySet()
V	get(Object key)
V	getQuietly(Object key)	Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
boolean	isEmpty()
Set<K>	keySet()
V	put(K key, V value)
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)
void	setCapacity(long capacity)	Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.
int	size()
Collection<V>	values()
long	weightedSize()	Returns the weighted size of this map.

Methods inherited from class java.util.AbstractMap

clone, equals, hashCode, putAll, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.concurrent.ConcurrentMap

compute, computeIfPresent, forEach, getOrDefault, merge, replaceAll

Methods inherited from interface java.util.Map

equals, hashCode, putAll

Method Details

capacity

public long capacity()

Retrieves the maximum weighted capacity of the map.

Returns:

the maximum weighted capacity

setCapacity

public void setCapacity(long capacity)

Sets the maximum weighted capacity of the map and eagerly evicts entries until it shrinks to the appropriate size.

Parameters:

capacity - the maximum weighted capacity of the map

Throws:

IllegalArgumentException - if the capacity is negative

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Map<K,V>

Overrides:

isEmpty in class AbstractMap<K,V>

size

public int size()

Specified by:

size in interface Map<K,V>

Overrides:

size in class AbstractMap<K,V>

weightedSize

public long weightedSize()

Returns the weighted size of this map.

Returns:

the combined weight of the values in this map

clear

public void clear()

Specified by:

clear in interface Map<K,V>

Overrides:

clear in class AbstractMap<K,V>

containsKey

public boolean containsKey(Object key)

Specified by:

containsKey in interface Map<K,V>

Overrides:

containsKey in class AbstractMap<K,V>

containsValue

public boolean containsValue(Object value)

Specified by:

containsValue in interface Map<K,V>

Overrides:

containsValue in class AbstractMap<K,V>

get

public V get(Object key)

Specified by:

get in interface Map<K,V>

Overrides:

get in class AbstractMap<K,V>

getQuietly

public V getQuietly(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. This method differs from get(Object) in that it does not record the operation with the page replacement policy.

Parameters:

key - the key whose associated value is to be returned

Returns:

the value to which the specified key is mapped, or null if this map contains no mapping for the key

Throws:

NullPointerException - if the specified key is null

put

public V put(K key,
 V value)

Specified by:

put in interface Map<K,V>

Overrides:

put in class AbstractMap<K,V>

putIfAbsent

public V putIfAbsent(K key,
 V value)

Specified by:

putIfAbsent in interface ConcurrentMap<K,V>

Specified by:

putIfAbsent in interface Map<K,V>

computeIfAbsent

public V computeIfAbsent(K key,
 Function<? super K,? extends V> mappingFunction)

If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map unless null. The entire method invocation is performed atomically, so the function is applied at most once per key. Some attempted update operations on this map by other threads may be blocked while computation is in progress, so the computation should be short and simple, and must not attempt to update any other mappings of this map.

Specified by:

computeIfAbsent in interface ConcurrentMap<K,V>

Specified by:

computeIfAbsent in interface Map<K,V>

Parameters:

key - key with which the specified value is to be associated

mappingFunction - the function to compute a value

Returns:

the current (existing or computed) value associated with the specified key, or null if the computed value is null

Throws:

NullPointerException - if the specified key or mappingFunction is null

IllegalStateException - if the computation detectably attempts a recursive update to this map that would otherwise never complete

RuntimeException - or Error if the mappingFunction does so, in which case the mapping is left unestablished

remove

public V remove(Object key)

Specified by:

remove in interface Map<K,V>

Overrides:

remove in class AbstractMap<K,V>

remove

public boolean remove(Object key,
 Object value)

Specified by:

remove in interface ConcurrentMap<K,V>

Specified by:

remove in interface Map<K,V>

replace

public V replace(K key,
 V value)

Specified by:

replace in interface ConcurrentMap<K,V>

Specified by:

replace in interface Map<K,V>

replace

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

Specified by:

replace in interface ConcurrentMap<K,V>

Specified by:

replace in interface Map<K,V>

keySet

public Set<K> keySet()

Specified by:

keySet in interface Map<K,V>

Overrides:

keySet in class AbstractMap<K,V>

ascendingKeySet

public Set<K> ascendingKeySet()

Returns a unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

Returns:

an ascending snapshot view of the keys in this map

ascendingKeySetWithLimit

public Set<K> ascendingKeySetWithLimit(int limit)

Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

Parameters:

limit - the maximum size of the returned set

Returns:

an ascending snapshot view of the keys in this map

Throws:

IllegalArgumentException - if the limit is negative

descendingKeySet

public Set<K> descendingKeySet()

Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

Returns:

a descending snapshot view of the keys in this map

descendingKeySetWithLimit

public Set<K> descendingKeySetWithLimit(int limit)

Returns an unmodifiable snapshot Set view of the keys contained in this map. The set's iterator returns the keys whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

Beware that, unlike in keySet(), obtaining the set is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the keys.

Parameters:

limit - the maximum size of the returned set

Returns:

a descending snapshot view of the keys in this map

Throws:

IllegalArgumentException - if the limit is negative

values

public Collection<V> values()

Specified by:

values in interface Map<K,V>

Overrides:

values in class AbstractMap<K,V>

entrySet

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

Specified by:

entrySet in interface Map<K,V>

Specified by:

entrySet in class AbstractMap<K,V>

ascendingMap

public Map<K,V> ascendingMap()

Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

Returns:

an ascending snapshot view of this map

ascendingMapWithLimit

public Map<K,V> ascendingMapWithLimit(int limit)

Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the ascending order in which its entries are considered eligible for retention, from the least-likely to be retained to the most-likely.

Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

Parameters:

limit - the maximum size of the returned map

Returns:

an ascending snapshot view of this map

Throws:

IllegalArgumentException - if the limit is negative

descendingMap

public Map<K,V> descendingMap()

Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

Returns:

a descending snapshot view of this map

descendingMapWithLimit

public Map<K,V> descendingMapWithLimit(int limit)

Returns an unmodifiable snapshot Map view of the mappings contained in this map. The map's collections return the mappings whose order of iteration is the descending order in which its entries are considered eligible for retention, from the most-likely to be retained to the least-likely.

Beware that obtaining the mappings is NOT a constant-time operation. Because of the asynchronous nature of the page replacement policy, determining the retention ordering requires a traversal of the entries.

Parameters:

limit - the maximum size of the returned map

Returns:

a descending snapshot view of this map

Throws:

IllegalArgumentException - if the limit is negative