EDU.oswego.cs.dl.util.concurrent
Class CopyOnWriteArraySet
AbstractSet
EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet
- Cloneable, java.io.Serializable
public class CopyOnWriteArraySet
extends AbstractSet
implements 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. ]
CopyOnWriteArraySet
public CopyOnWriteArraySet()
Constructs an empty set
CopyOnWriteArraySet
public CopyOnWriteArraySet(Collection c)
Constructs a set containing all of the elements of the specified
Collection.
add
public boolean add(Object o)
addAll
public boolean addAll(Collection c)
contains
public boolean contains(Object o)
containsAll
public boolean containsAll(Collection c)
isEmpty
public boolean isEmpty()
iterator
public Iterator iterator()
remove
public boolean remove(Object o)
removeAll
public boolean removeAll(Collection c)
retainAll
public boolean retainAll(Collection c)
toArray
public Object[] toArray()
toArray
public Object[] toArray(Object[] a)