Examples of PhantomReference

java.lang.ref.PhantomReference
Phantom reference objects, which are enqueued after the collector determines that their referents may otherwise be reclaimed. Phantom references are most often used for scheduling pre-mortem cleanup actions in a more flexible way than is possible with the Java finalization mechanism.
If the garbage collector determines at a certain point in time that the referent of a phantom reference is phantom reachable, then at that time or at some later time it will enqueue the reference.
In order to ensure that a reclaimable object remains so, the referent of a phantom reference may not be retrieved: The get method of a phantom reference always returns null.
Unlike soft and weak references, phantom references are not automatically cleared by the garbage collector as they are enqueued. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable. @version 1.20, 11/17/05 @author Mark Reinhold @since 1.2

Examples of java.lang.ref.PhantomReference

    }
    
    public void testCanUseDifferentMapImplementation() throws InterruptedException {
        String value = new String("value");
        ReferenceQueue refQueue = new ReferenceQueue();
        Reference ref = new PhantomReference(value, refQueue);
        
        Map map = new WeakCache(new TreeMap());
        map.put("key", value);
        value = null;


        int i = 0;
        while (refQueue.poll() == null) {
            ref.get(); // always null
            assertTrue("Value still alive even after "+i+" forced garbage collections", i++ < 5);
            Thread.sleep(10);
            System.gc();
        }
        assertEquals(0, map.size());

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Examples of java.lang.ref.PhantomReference

     * @param interceptor    ignored
     * @param connectionInfo the connection that was released
     * @param action         ignored
     */
    public void handleReleased(final ConnectionTrackingInterceptor interceptor, final ConnectionInfo connectionInfo, final ConnectionReturnAction action) {
        final PhantomReference phantomReference = references.remove(connectionInfo.getManagedConnectionInfo());
        if (phantomReference != null) {
            phantomReference.clear();
        }
    }

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Examples of java.lang.ref.PhantomReference

   * @tests java.lang.ref.PhantomReference#get()
   */
  public void test_get() {
    ReferenceQueue rq = new ReferenceQueue();
    bool = new Boolean(false);
    PhantomReference pr = new PhantomReference(bool, rq);
    assertNull("Same object returned.", pr.get());
  }

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Examples of java.lang.ref.PhantomReference

   *        java.lang.ref.ReferenceQueue)
   */
  public void test_ConstructorLjava_lang_ObjectLjava_lang_ref_ReferenceQueue() throws Exception {
    ReferenceQueue rq = new ReferenceQueue();
    bool = new Boolean(true);
                PhantomReference pr = new PhantomReference(bool, rq);
                // Allow the finalizer to run to potentially enqueue
                Thread.sleep(1000);
                assertTrue("Initialization failed.", !pr.isEnqueued());


                // need a reference to bool so the jit does not optimize it away
    assertTrue("should always pass", bool.booleanValue());


    boolean exception = false;
    try {
      new PhantomReference(bool, null);
    } catch (NullPointerException e) {
      exception = true;
    }
    assertTrue("Should not throw NullPointerException", !exception);
  }

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Examples of java.lang.ref.PhantomReference

     * @param obj the object on which to wait
     */
    public WaitUnreachable(Object obj) {
        this.obj = obj;
        queue = new ReferenceQueue();
        ref = new PhantomReference(obj, queue);
    }

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Examples of java.lang.ref.PhantomReference

        try {
            synchronized (monitor) {
                if (display == null) {
                    return null;
                }
                phantomImage = new PhantomReference(display, refQueue);
                String icon = "images/duke.gif";
                bgImg = ImageIO.read(getClass().getResourceAsStream(icon));
                mt = new MediaTracker(this);
                mt.addImage(bgImg, hashCode());
                mt.addImage(display, hashCode());

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Examples of java.lang.ref.PhantomReference

     * @param interceptor    ignored
     * @param connectionInfo the connection that was released
     * @param action         ignored
     */
    public void handleReleased(final ConnectionTrackingInterceptor interceptor, final ConnectionInfo connectionInfo, final ConnectionReturnAction action) {
        final PhantomReference phantomReference = references.remove(connectionInfo.getManagedConnectionInfo());
        if (phantomReference != null) {
            phantomReference.clear();
        }
    }

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Examples of java.lang.ref.PhantomReference

     * @param obj the object on which to wait
     */
    public WaitUnreachable(Object obj) {
        this.obj = obj;
        queue = new ReferenceQueue();
        ref = new PhantomReference(obj, queue);
    }

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Examples of java.lang.ref.PhantomReference

    ReferenceQueue q = new ReferenceQueue();


    Reference ar = new WeakReference(a);
    Reference br = new WeakReference(b, q);
    Reference cr = new WeakReference(c, q);
    Reference dr = new PhantomReference(d, q);
    Reference er = new MyReference(e, q, "foo");
    
    WeakHashMap<Key,Object> map = new WeakHashMap();
    map.put(new Key("foo"), f);


    a = b = c = d = e = cr = null;
    
    System.out.println("a: " + ar.get());
    System.out.println("b: " + br.get());
    System.out.println("d: " + dr.get());
    System.out.println("e: " + er.get());
    System.out.println("f: " + map.get(new Key("foo")));


    System.gc();


    System.out.println("a: " + ar.get());
    System.out.println("b: " + br.get());
    System.out.println("d: " + dr.get());
    System.out.println("e: " + er.get());
    System.out.println("f: " + map.get(new Key("foo")));


    for (Reference r = q.poll(); r != null; r = q.poll()) {
      System.out.println("polled: " + r.get());

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Examples of java.lang.ref.PhantomReference

        if (target instanceof DisposerTarget) {
            target = ((DisposerTarget)target).getDisposerReferent();
        }
        java.lang.ref.Reference ref;
        if (refType == PHANTOM) {
            ref = new PhantomReference(target, queue);
        } else {
            ref = new WeakReference(target, queue);
        }
        records.put(ref, rec);
    }

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