org.apache.openjpa.lib.util.concurrent

Class ConcurrentReferenceHashMap

java.lang.Object

java.util.AbstractMap

org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashMap

All Implemented Interfaces:

Cloneable, Map, ConcurrentMap, ReferenceMap, SizedMap

public class ConcurrentReferenceHashMap
extends AbstractMap
implements ConcurrentMap, ReferenceMap, SizedMap, Cloneable

This class implements a HashMap which has limited synchronization and reference keys or values(but not both). In particular mutators are generally synchronized while accessors are generally not. Additionally the Iterators returned by this class are not "fail-fast", but instead try to continue to iterate over the data structure after changes have been made. Finally purging of the reference queue is only done inside mutators. Null keys are not supported if keys use references. Null values are not supported if values use references. This class is based heavily on the WeakHashMap class in the Java collections package.

Nested Class Summary

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

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

Constructor Summary

Constructors

Constructor and Description
ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType) Constructs a new, empty HashMap with a default capacity and load factor.
ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int initialCapacity) Constructs a new, empty HashMap with the specified initial capacity and default load factor.
ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, int initialCapacity, float loadFactor) Constructs a new, empty HashMap with the specified initial capacity and the specified load factor.
ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType, AbstractReferenceMap.ReferenceStrength valueType, Map t) Constructs a new HashMap with the same mappings as the given Map.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all mappings from this HashMap.
Object	clone() Returns a shallow copy of this HashMap.
boolean	containsKey(Object key) Returns true if this HashMap contains a mapping for the specified key.
boolean	containsValue(Object value) Returns true if this HashMap maps one or more keys to the specified value.
Set	entrySet() Returns a Collection view of the mappings contained in this HashMap.
protected boolean	eq(Object x, Object y) Compare two objects.
Object	get(Object key) Returns the value to which this HashMap maps the specified key.
int	getMaxSize() The maximum number of entries, or Integer.MAX_VALUE for no limit.
protected int	hc(Object o) Obtain the hashcode of an object.
boolean	isEmpty() Returns true if this Map contains no key-value mappings.
boolean	isFull() Whether the map is full.
void	keyExpired(Object value) Overridable callback for when a key reference expires.
Set	keySet() Returns a Set view of the keys contained in this HashMap.
void	overflowRemoved(Object key, Object value) Overridable callback for when an overflow entry is automatically removed.
Object	put(Object key, Object value) Associates the specified value with the specified key in this HashMap.
void	putAll(Map t) Copies all of the mappings from the specified Map to this HashMap These mappings will replace any mappings that this HashMap had for any of the keys currently in the specified Map.
Iterator	randomEntryIterator() Iterate over map entries, beginning at an arbitrary (not strictly random) entry.
Object	remove(Object key) Removes the mapping for this key from this HashMap if present.
void	removeExpired() Purge stale entries.
Map.Entry	removeRandom() Remove an arbitrary(not strictly random) entry from the map.
void	setMaxSize(int maxSize) The maximum number of entries, or Integer.MAX_VALUE for no limit.
int	size() Returns the number of key-value mappings in this Map.
void	valueExpired(Object key) Overridable callback for when a value reference expires.
Collection	values() Returns a Collection view of the values contained in this HashMap.

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, putIfAbsent, remove, replace, replace, replaceAll

Constructor Detail

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType,
                                  AbstractReferenceMap.ReferenceStrength valueType,
                                  int initialCapacity,
                                  float loadFactor)

Constructs a new, empty HashMap with the specified initial capacity and the specified load factor.

Parameters:

keyType - the reference type of map keys

valueType - the reference type of map values

initialCapacity - the initial capacity of the HashMap.

loadFactor - a number between 0.0 and 1.0.

Throws:

IllegalArgumentException - if neither keys nor values use hard references, if the initial capacity is less than or equal to zero, or if the load factor is less than or equal to zero

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType,
                                  AbstractReferenceMap.ReferenceStrength valueType,
                                  int initialCapacity)

Constructs a new, empty HashMap with the specified initial capacity and default load factor.

Parameters:

keyType - the reference type of map keys

valueType - the reference type of map values

initialCapacity - the initial capacity of the HashMap.

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType,
                                  AbstractReferenceMap.ReferenceStrength valueType)

Constructs a new, empty HashMap with a default capacity and load factor.

Parameters:

keyType - the reference type of map keys

valueType - the reference type of map values

ConcurrentReferenceHashMap

public ConcurrentReferenceHashMap(AbstractReferenceMap.ReferenceStrength keyType,
                                  AbstractReferenceMap.ReferenceStrength valueType,
                                  Map t)

Constructs a new HashMap with the same mappings as the given Map. The HashMap is created with a capacity of thrice the number of entries in the given Map or 11 (whichever is greater), and a default load factor.

Parameters:

keyType - the reference type of map keys

valueType - the reference type of map values

Method Detail

eq

protected boolean eq(Object x,
                     Object y)

Compare two objects. These might be keys, values, or Entry instances. This implementation uses a normal null-safe object equality algorithm.

Since:

1.0.0

hc

protected int hc(Object o)

Obtain the hashcode of an object. The object might be a key, a value, or an Entry. This implementation just delegates to Object.hashCode()

Since:

1.0.0

getMaxSize

public int getMaxSize()

Description copied from interface: SizedMap

The maximum number of entries, or Integer.MAX_VALUE for no limit.

Specified by:

getMaxSize in interface SizedMap

setMaxSize

public void setMaxSize(int maxSize)

Description copied from interface: SizedMap

The maximum number of entries, or Integer.MAX_VALUE for no limit.

Specified by:

setMaxSize in interface SizedMap

isFull

public boolean isFull()

Description copied from interface: SizedMap

Whether the map is full.

Specified by:

isFull in interface SizedMap

overflowRemoved

public void overflowRemoved(Object key,
                            Object value)

Description copied from interface: SizedMap

Overridable callback for when an overflow entry is automatically removed.

Specified by:

overflowRemoved in interface SizedMap

size

public int size()

Returns the number of key-value mappings in this Map. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.

Specified by:

size in interface Map

Overrides:

size in class AbstractMap

isEmpty

public boolean isEmpty()

Returns true if this Map contains no key-value mappings. This result is a snapshot, and may not reflect unprocessed entries that will be removed before next attempted access because they are no longer referenced.

Specified by:

isEmpty in interface Map

Overrides:

isEmpty in class AbstractMap

containsValue

public boolean containsValue(Object value)

Returns true if this HashMap maps one or more keys to the specified value.

Specified by:

containsValue in interface Map

Overrides:

containsValue in class AbstractMap

Parameters:

value - value whose presence in this Map is to be tested.

containsKey

public boolean containsKey(Object key)

Returns true if this HashMap contains a mapping for the specified key.

Specified by:

containsKey in interface Map

Overrides:

containsKey in class AbstractMap

Parameters:

key - key whose presence in this Map is to be tested.

get

public Object get(Object key)

Returns the value to which this HashMap maps the specified key. Returns null if the HashMap contains no mapping for this key.

Specified by:

get in interface Map

Overrides:

get in class AbstractMap

Parameters:

key - key whose associated value is to be returned.

put

public Object put(Object key,
                  Object value)

Associates the specified value with the specified key in this HashMap. If the HashMap previously contained a mapping for this key, the old value is replaced.

Specified by:

put in interface Map

Overrides:

put in class AbstractMap

Parameters:

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

value - value to be associated with the specified key.

Returns:

previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the HashMap previously associated null with the specified key.

remove

public Object remove(Object key)

Removes the mapping for this key from this HashMap if present.

Specified by:

remove in interface Map

Overrides:

remove in class AbstractMap

Parameters:

key - key whose mapping is to be removed from the Map.

Returns:

previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the HashMap previously associated null with the specified key.

removeExpired

public void removeExpired()

Description copied from interface: ReferenceMap

Purge stale entries.

Specified by:

removeExpired in interface ReferenceMap

keyExpired

public void keyExpired(Object value)

Description copied from interface: ReferenceMap

Overridable callback for when a key reference expires.

Specified by:

keyExpired in interface ReferenceMap

Parameters:

value - the value for the expired key

valueExpired

public void valueExpired(Object key)

Description copied from interface: ReferenceMap

Overridable callback for when a value reference expires.

Specified by:

valueExpired in interface ReferenceMap

Parameters:

key - the key for the expired value

removeRandom

public Map.Entry removeRandom()

Description copied from interface: ConcurrentMap

Remove an arbitrary(not strictly random) entry from the map. This allows implementation of concurrent caches with size ceilings.

Specified by:

removeRandom in interface ConcurrentMap

Returns:

the removed entry, or null if map is empty

randomEntryIterator

public Iterator randomEntryIterator()

Description copied from interface: ConcurrentMap

Iterate over map entries, beginning at an arbitrary (not strictly random) entry.

Specified by:

randomEntryIterator in interface ConcurrentMap

putAll

public void putAll(Map t)

Copies all of the mappings from the specified Map to this HashMap These mappings will replace any mappings that this HashMap had for any of the keys currently in the specified Map.

Specified by:

putAll in interface Map

Overrides:

putAll in class AbstractMap

Parameters:

t - Mappings to be stored in this Map.

clear

public void clear()

Removes all mappings from this HashMap.

Specified by:

clear in interface Map

Overrides:

clear in class AbstractMap

clone

public Object clone()

Returns a shallow copy of this HashMap. The keys and values themselves are not cloned.

Overrides:

clone in class AbstractMap

keySet

public Set keySet()

Returns a Set view of the keys contained in this HashMap. The Set is backed by the HashMap, so changes to the HashMap are reflected in the Set, and vice-versa. The Set supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

keySet in interface Map

Overrides:

keySet in class AbstractMap

values

public Collection values()

Returns a Collection view of the values contained in this HashMap. The Collection is backed by the HashMap, so changes to the HashMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface Map

Overrides:

values in class AbstractMap

entrySet

public Set entrySet()

Returns a Collection view of the mappings contained in this HashMap. Each element in the returned collection is a Map.Entry. The Collection is backed by the HashMap, so changes to the HashMap are reflected in the Collection, and vice-versa. The Collection supports element removal, which removes the corresponding mapping from the HashMap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

entrySet in interface Map

Specified by:

entrySet in class AbstractMap

See Also:

Map.Entry