com.blogspot.mydailyjava.weaklockfree

Class AbstractWeakConcurrentMap<K,V,L>

java.lang.Object

java.lang.ref.ReferenceQueue<K>

com.blogspot.mydailyjava.weaklockfree.AbstractWeakConcurrentMap<K,V,L>

All Implemented Interfaces:

Iterable<Map.Entry<K,V>>, Runnable

Direct Known Subclasses:

WeakConcurrentMap

public abstract class AbstractWeakConcurrentMap<K,V,L>
extends ReferenceQueue<K>
implements Runnable, Iterable<Map.Entry<K,V>>

A thread-safe map with weak keys. Entries are based on a key's system hash code and keys are considered equal only by reference equality. This class offers an abstract-base implementation that allows to override methods.

This class does not implement the Map interface because this implementation is incompatible with the map contract. While iterating over a map's entries, any key that has not passed iteration is referenced non-weakly.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AbstractWeakConcurrentMap.WeakKey<K>

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractWeakConcurrentMap()
protected	AbstractWeakConcurrentMap(ConcurrentMap<AbstractWeakConcurrentMap.WeakKey<K>,V> target)

Method Summary

Modifier and Type	Method and Description
int	approximateSize() Returns the approximate size of this map where the returned number is at least as big as the actual number of entries.
void	clear() Clears the entire map.
boolean	containsKey(K key)
protected V	defaultValue(K key) Creates a default value.
void	expungeStaleEntries() Cleans all unused references.
V	get(K key)
V	getIfPresent(K key)
protected abstract L	getLookupKey(K key) Override with care as it can cause lookup failures if done incorrectly.
Iterator<Map.Entry<K,V>>	iterator()
V	put(K key, V value)
V	putIfAbsent(K key, V value)
V	putIfProbablyAbsent(K key, V value)
V	remove(K key)
protected abstract void	resetLookupKey(L lookupKey) Resets any reusable state in the lookup key.
void	run()
String	toString()

Methods inherited from class java.lang.ref.ReferenceQueue

poll, remove, remove

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

AbstractWeakConcurrentMap

protected AbstractWeakConcurrentMap()

AbstractWeakConcurrentMap

protected AbstractWeakConcurrentMap(ConcurrentMap<AbstractWeakConcurrentMap.WeakKey<K>,V> target)

Parameters:

target - ConcurrentMap implementation that this class wraps.

Method Detail

getLookupKey

protected abstract L getLookupKey(K key)

Override with care as it can cause lookup failures if done incorrectly. The result must have the same Object.hashCode() as the input and be equal to a weak reference of the key. When overriding this, also override resetLookupKey(L).

resetLookupKey

protected abstract void resetLookupKey(L lookupKey)

Resets any reusable state in the lookup key.

get

public V get(K key)

Parameters:

key - The key of the entry.

Returns:

The value of the entry or the default value if it did not exist.

getIfPresent

public V getIfPresent(K key)

Parameters:

key - The key of the entry.

Returns:

The value of the entry or null if it did not exist.

containsKey

public boolean containsKey(K key)

Parameters:

key - The key of the entry.

Returns:

true if the key already defines a value.

put

public V put(K key,
             V value)

Parameters:

key - The key of the entry.

value - The value of the entry.

Returns:

The previous entry or null if it does not exist.

putIfAbsent

public V putIfAbsent(K key,
                     V value)

Parameters:

key - The key of the entry.

value - The value of the entry.

Returns:

The previous entry or null if it does not exist.

putIfProbablyAbsent

public V putIfProbablyAbsent(K key,
                             V value)

Parameters:

key - The key of the entry.

value - The value of the entry.

Returns:

The previous entry or null if it does not exist.

remove

public V remove(K key)

Parameters:

key - The key of the entry.

Returns:

The removed entry or null if it does not exist.

clear

public void clear()

Clears the entire map.

defaultValue

protected V defaultValue(K key)

Creates a default value. There is no guarantee that the requested value will be set as a once it is created in case that another thread requests a value for a key concurrently.

Parameters:

key - The key for which to create a default value.

Returns:

The default value for a key without value or null for not defining a default value.

expungeStaleEntries

public void expungeStaleEntries()

Cleans all unused references.

approximateSize

public int approximateSize()

Returns the approximate size of this map where the returned number is at least as big as the actual number of entries.

Returns:

The minimum size of this map.

run

public void run()

Specified by:

run in interface Runnable

iterator

public Iterator<Map.Entry<K,V>> iterator()

Specified by:

iterator in interface Iterable<Map.Entry<K,V>>

toString

public String toString()

Overrides:

toString in class Object