java.lang.ref
Class ReferenceQueue

java.lang.Object
  java.lang.ref.ReferenceQueue

Direct Known Subclasses:

ReferenceQueue.Null

public class ReferenceQueue

extends Object

Reference queues, to which registered reference objects are appended by the garbage collector after the appropriate reachability changes are detected.

Since:

1.2

Author:

Mark Reinhold

Nested Class Summary

private static class	ReferenceQueue.Lock
private static class	ReferenceQueue.Null

Field Summary

(package private) static ReferenceQueue	ENQUEUED
private Reference	head
private ReferenceQueue.Lock	lock
(package private) static ReferenceQueue	NULL
private long	queueLength

Constructor Summary

ReferenceQueue()
Constructs a new reference-object queue.

Method Summary

(package private) boolean	enqueue(Reference r)
Reference	poll() Polls this queue to see if a reference object is available.
private Reference	reallyPoll()
Reference	remove() Removes the next reference object in this queue, blocking until one becomes available.
Reference	remove(long timeout) Removes the next reference object in this queue, blocking until either one becomes available or the given timeout period expires.

Methods inherited from class java.lang.Object

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

Field Detail

NULL

static ReferenceQueue NULL

ENQUEUED

static ReferenceQueue ENQUEUED

lock

private ReferenceQueue.Lock lock

head

private Reference head

queueLength

private long queueLength

Constructor Detail

ReferenceQueue

public ReferenceQueue()

Constructs a new reference-object queue.

Method Detail

enqueue

boolean enqueue(Reference r)

reallyPoll

private Reference reallyPoll()

poll

public Reference poll()

Polls this queue to see if a reference object is available. If one is available without further delay then it is removed from the queue and returned. Otherwise this method immediately returns null.

Returns:

A reference object, if one was immediately available, otherwise null

remove

public Reference remove(long timeout)
                 throws IllegalArgumentException,
                        InterruptedException

Removes the next reference object in this queue, blocking until either one becomes available or the given timeout period expires.

This method does not offer real-time guarantees: It schedules the timeout as if by invoking the Object.wait(long) method.

Parameters:

timeout - If positive, block for up timeout milliseconds while waiting for a reference to be added to this queue. If zero, block indefinitely.

Returns:

A reference object, if one was available within the specified timeout period, otherwise null

Throws:

IllegalArgumentException - If the value of the timeout argument is negative

InterruptedException - If the timeout wait is interrupted

remove

public Reference remove()
                 throws InterruptedException

Removes the next reference object in this queue, blocking until one becomes available.

Returns:

A reference object, blocking until one becomes available

Throws:

InterruptedException - If the wait is interrupted