8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.ref;
27
28 import jdk.internal.vm.annotation.IntrinsicCandidate;
29
30 /**
31 * Phantom reference objects, which are enqueued after the collector
32 * determines that their referents may otherwise be reclaimed. Phantom
33 * references are most often used to schedule post-mortem cleanup actions.
34 *
35 * <p> Suppose the garbage collector determines at a certain point in time
36 * that an object is <a href="package-summary.html#reachability">
37 * phantom reachable</a>. At that time it will atomically clear
38 * all phantom references to that object and all phantom references to
39 * any other phantom-reachable objects from which that object is reachable.
40 * At the same time or at some later time it will enqueue those newly-cleared
41 * phantom references that are registered with reference queues.
42 *
43 * <p> In order to ensure that a reclaimable object remains so, the referent of
44 * a phantom reference may not be retrieved: The {@code get} method of a
45 * phantom reference always returns {@code null}.
46 * The {@link #refersTo(Object) refersTo} method can be used to test
47 * whether some object is the referent of a phantom reference.
48 * @param <T> the type of the referent
49 *
50 * @author Mark Reinhold
51 * @since 1.2
52 */
53
54 public non-sealed class PhantomReference<T> extends Reference<T> {
83 * do reference processing concurrently.
84 */
85 @Override
86 void clearImpl() {
87 clear0();
88 }
89
90 @IntrinsicCandidate
91 private native void clear0();
92
93 /**
94 * Creates a new phantom reference that refers to the given object and
95 * is registered with the given queue.
96 *
97 * <p> It is possible to create a phantom reference with a {@code null}
98 * queue. Such a reference will never be enqueued.
99 *
100 * @param referent the object the new phantom reference will refer to
101 * @param q the queue with which the reference is to be registered,
102 * or {@code null} if registration is not required
103 */
104 public PhantomReference(T referent, ReferenceQueue<? super T> q) {
105 super(referent, q);
106 }
107
108 }
|
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.ref;
27
28 import java.util.Objects;
29 import jdk.internal.vm.annotation.IntrinsicCandidate;
30
31 /**
32 * Phantom reference objects, which are enqueued after the collector
33 * determines that their referents may otherwise be reclaimed. Phantom
34 * references are most often used to schedule post-mortem cleanup actions.
35 *
36 * <div class="preview-block">
37 * <div class="preview-comment">
38 * The referent must have {@linkplain Objects#hasIdentity(Object) object identity}.
39 * When preview features are enabled, attempts to create a reference
40 * to a {@linkplain Class#isValue value object} result in an {@link IdentityException}.
41 * </div>
42 * </div>
43 *
44 * <p> Suppose the garbage collector determines at a certain point in time
45 * that an object is <a href="package-summary.html#reachability">
46 * phantom reachable</a>. At that time it will atomically clear
47 * all phantom references to that object and all phantom references to
48 * any other phantom-reachable objects from which that object is reachable.
49 * At the same time or at some later time it will enqueue those newly-cleared
50 * phantom references that are registered with reference queues.
51 *
52 * <p> In order to ensure that a reclaimable object remains so, the referent of
53 * a phantom reference may not be retrieved: The {@code get} method of a
54 * phantom reference always returns {@code null}.
55 * The {@link #refersTo(Object) refersTo} method can be used to test
56 * whether some object is the referent of a phantom reference.
57 * @param <T> the type of the referent
58 *
59 * @author Mark Reinhold
60 * @since 1.2
61 */
62
63 public non-sealed class PhantomReference<T> extends Reference<T> {
92 * do reference processing concurrently.
93 */
94 @Override
95 void clearImpl() {
96 clear0();
97 }
98
99 @IntrinsicCandidate
100 private native void clear0();
101
102 /**
103 * Creates a new phantom reference that refers to the given object and
104 * is registered with the given queue.
105 *
106 * <p> It is possible to create a phantom reference with a {@code null}
107 * queue. Such a reference will never be enqueued.
108 *
109 * @param referent the object the new phantom reference will refer to
110 * @param q the queue with which the reference is to be registered,
111 * or {@code null} if registration is not required
112 * @throws IdentityException if the referent is not an
113 * {@link java.util.Objects#hasIdentity(Object) identity object}
114 */
115 public PhantomReference(T referent, ReferenceQueue<? super T> q) {
116 super(referent, q);
117 }
118
119 }
|