EDU.oswego.cs.dl.util.concurrent

Class CopyOnWriteArraySet

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractSet

EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.lang.Iterable, java.util.Collection, java.util.Set

public class CopyOnWriteArraySet
extends java.util.AbstractSet
implements java.lang.Cloneable, java.io.Serializable

This class implements a java.util.Set that uses a CopyOnWriteArrayList for all of its operations. Thus, it shares the same basic properties:

• It is best suited for applications in which set sizes generally stay small, read-only operations vastly outnumber mutative operations, and you need to prevent interference among threads during traversal.
• Mutative operations(add, set, remove, etc) are fairly expensive since they usually entail copying the entire underlying array.
• Loops involving repeated element-by-element mutative operations are so expensive that they should generally be avoided.
• Iterators do not support the mutative remove operation
• Traversal via iterators is very fast and cannot ever encounter interference from other threads. Iterators rely on unchanging snapshots of the array at the time the iterators were constructed

Sample Usage. Probably the main application of copy-on-write sets are classes that maintain sets of Handler objects that must be multicasted to upon an update command. This is a classic case where you do not want to be holding a synch lock while sending a message, and where traversals normally vastly overwhelm additions.

 class  Handler { void handle(); ... }

 class X {
    private final CopyOnWriteArraySet handlers = new CopyOnWriteArraySet();
    public void addHandler(Handler h) { handlers.add(h); }
   
    private long internalState;
    private synchronized void changeState() { internalState = ...; }
 
    public void update() {
       changeState();
       Iterator it = handlers.iterator();
       while (it.hasNext())
          ((Handler)(it.next()).handle();
    }
 }
 

[ Introduction to this package. ]

See Also:

CopyOnWriteArrayList, Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected CopyOnWriteArrayList	al

Constructor Summary

Constructors

Constructor and Description
CopyOnWriteArraySet() Constructs an empty set
CopyOnWriteArraySet(java.util.Collection c) Constructs a set containing all of the elements of the specified Collection.

Method Summary

Modifier and Type	Method and Description
boolean	add(java.lang.Object o)
boolean	addAll(java.util.Collection c)
void	clear()
boolean	contains(java.lang.Object o)
boolean	containsAll(java.util.Collection c)
boolean	isEmpty()
java.util.Iterator	iterator()
boolean	remove(java.lang.Object o)
boolean	removeAll(java.util.Collection c)
boolean	retainAll(java.util.Collection c)
int	size()
java.lang.Object[]	toArray()
java.lang.Object[]	toArray(java.lang.Object[] a)

Methods inherited from class java.util.AbstractSet

equals, hashCode

Methods inherited from class java.util.AbstractCollection

toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Set

spliterator

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

al

protected final CopyOnWriteArrayList al

Constructor Detail

CopyOnWriteArraySet

public CopyOnWriteArraySet()

Constructs an empty set

CopyOnWriteArraySet

public CopyOnWriteArraySet(java.util.Collection c)

Constructs a set containing all of the elements of the specified Collection.

Method Detail

size

public int size()

Specified by:

size in interface java.util.Collection

Specified by:

size in interface java.util.Set

Specified by:

size in class java.util.AbstractCollection

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface java.util.Collection

Specified by:

isEmpty in interface java.util.Set

Overrides:

isEmpty in class java.util.AbstractCollection

contains

public boolean contains(java.lang.Object o)

Specified by:

contains in interface java.util.Collection

Specified by:

contains in interface java.util.Set

Overrides:

contains in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray()

Specified by:

toArray in interface java.util.Collection

Specified by:

toArray in interface java.util.Set

Overrides:

toArray in class java.util.AbstractCollection

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)

Specified by:

toArray in interface java.util.Collection

Specified by:

toArray in interface java.util.Set

Overrides:

toArray in class java.util.AbstractCollection

clear

public void clear()

Specified by:

clear in interface java.util.Collection

Specified by:

clear in interface java.util.Set

Overrides:

clear in class java.util.AbstractCollection

iterator

public java.util.Iterator iterator()

Specified by:

iterator in interface java.lang.Iterable

Specified by:

iterator in interface java.util.Collection

Specified by:

iterator in interface java.util.Set

Specified by:

iterator in class java.util.AbstractCollection

remove

public boolean remove(java.lang.Object o)

Specified by:

remove in interface java.util.Collection

Specified by:

remove in interface java.util.Set

Overrides:

remove in class java.util.AbstractCollection

containsAll

public boolean containsAll(java.util.Collection c)

Specified by:

containsAll in interface java.util.Collection

Specified by:

containsAll in interface java.util.Set

Overrides:

containsAll in class java.util.AbstractCollection

addAll

public boolean addAll(java.util.Collection c)

Specified by:

addAll in interface java.util.Collection

Specified by:

addAll in interface java.util.Set

Overrides:

addAll in class java.util.AbstractCollection

removeAll

public boolean removeAll(java.util.Collection c)

Specified by:

removeAll in interface java.util.Collection

Specified by:

removeAll in interface java.util.Set

Overrides:

removeAll in class java.util.AbstractSet

retainAll

public boolean retainAll(java.util.Collection c)

Specified by:

retainAll in interface java.util.Collection

Specified by:

retainAll in interface java.util.Set

Overrides:

retainAll in class java.util.AbstractCollection

add

public boolean add(java.lang.Object o)

Specified by:

add in interface java.util.Collection

Specified by:

add in interface java.util.Set

Overrides:

add in class java.util.AbstractCollection