com.blogspot.mydailyjava.weaklockfree

Class WeakConcurrentMap<K,V>

java.lang.Object

java.lang.ref.ReferenceQueue<K>

com.blogspot.mydailyjava.weaklockfree.WeakConcurrentMap<K,V>

All Implemented Interfaces:

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

Direct Known Subclasses:

WeakConcurrentMap.WithInlinedExpunction

public class WeakConcurrentMap<K,V>
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 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	WeakConcurrentMap.WithInlinedExpunction<K,V> A WeakConcurrentMap where stale entries are removed as a side effect of interacting with this map.

Constructor Summary

Constructors

Constructor and Description
WeakConcurrentMap(boolean cleanerThread)
WeakConcurrentMap(boolean cleanerThread, boolean reuseKeys)

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)
Thread	getCleanerThread()
V	getIfPresent(K key)
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)
void	run()

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, toString, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

WeakConcurrentMap

public WeakConcurrentMap(boolean cleanerThread)

Parameters:

cleanerThread - true if a thread should be started that removes stale entries.

WeakConcurrentMap

public WeakConcurrentMap(boolean cleanerThread,
                         boolean reuseKeys)

Parameters:

cleanerThread - true if a thread should be started that removes stale entries.

reuseKeys - true if the lookup keys should be reused via a ThreadLocal. Note that setting this to true may result in class loader leaks. See isPersistentClassLoader(ClassLoader) for more details.

Method Detail

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.

getCleanerThread

public Thread getCleanerThread()

Returns:

The cleaner thread or null if no such thread was set.

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>>