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 /**
29 * Reference queues, to which registered reference objects are appended by the
30 * garbage collector after the appropriate reachability changes are detected.
31 *
32 * @author Mark Reinhold
33 * @since 1.2
34 */
35
36 public class ReferenceQueue<T> {
37
38 /**
39 * Constructs a new reference-object queue.
40 */
41 public ReferenceQueue() { }
42
43 private static class Null<S> extends ReferenceQueue<S> {
44 boolean enqueue(Reference<? extends S> r) {
45 return false;
46 }
47 }
66 r.queue = ENQUEUED;
67 r.next = (head == null) ? r : head;
68 head = r;
69 queueLength++;
70 if (r instanceof FinalReference) {
71 sun.misc.VM.addFinalRefCount(1);
72 }
73 lock.notifyAll();
74 return true;
75 }
76 }
77
78 @SuppressWarnings("unchecked")
79 private Reference<? extends T> reallyPoll() { /* Must hold lock */
80 Reference<? extends T> r = head;
81 if (r != null) {
82 head = (r.next == r) ?
83 null :
84 r.next; // Unchecked due to the next field having a raw type in Reference
85 r.queue = NULL;
86 r.next = r;
87 queueLength--;
88 if (r instanceof FinalReference) {
89 sun.misc.VM.addFinalRefCount(-1);
90 }
91 return r;
92 }
93 return null;
94 }
95
96 /**
97 * Polls this queue to see if a reference object is available. If one is
98 * available without further delay then it is removed from the queue and
99 * returned. Otherwise this method immediately returns <tt>null</tt>.
100 *
101 * @return A reference object, if one was immediately available,
102 * otherwise <code>null</code>
103 */
104 public Reference<? extends T> poll() {
105 if (head == null)
147 long end = System.nanoTime();
148 timeout -= (end - start) / 1000_000;
149 if (timeout <= 0) return null;
150 start = end;
151 }
152 }
153 }
154 }
155
156 /**
157 * Removes the next reference object in this queue, blocking until one
158 * becomes available.
159 *
160 * @return A reference object, blocking until one becomes available
161 * @throws InterruptedException If the wait is interrupted
162 */
163 public Reference<? extends T> remove() throws InterruptedException {
164 return remove(0);
165 }
166
167 }
|
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 sun.misc.Unsafe;
29 import java.util.function.Consumer;
30
31 /**
32 * Reference queues, to which registered reference objects are appended by the
33 * garbage collector after the appropriate reachability changes are detected.
34 *
35 * @author Mark Reinhold
36 * @since 1.2
37 */
38
39 public class ReferenceQueue<T> {
40
41 /**
42 * Constructs a new reference-object queue.
43 */
44 public ReferenceQueue() { }
45
46 private static class Null<S> extends ReferenceQueue<S> {
47 boolean enqueue(Reference<? extends S> r) {
48 return false;
49 }
50 }
69 r.queue = ENQUEUED;
70 r.next = (head == null) ? r : head;
71 head = r;
72 queueLength++;
73 if (r instanceof FinalReference) {
74 sun.misc.VM.addFinalRefCount(1);
75 }
76 lock.notifyAll();
77 return true;
78 }
79 }
80
81 @SuppressWarnings("unchecked")
82 private Reference<? extends T> reallyPoll() { /* Must hold lock */
83 Reference<? extends T> r = head;
84 if (r != null) {
85 head = (r.next == r) ?
86 null :
87 r.next; // Unchecked due to the next field having a raw type in Reference
88 r.queue = NULL;
89 // make sure the store to r.next below doesn't float up
90 // before the store to r.queue above because we need this
91 // for correct lock-less iteration in forEach()
92 U.storeFence();
93 r.next = r;
94 queueLength--;
95 if (r instanceof FinalReference) {
96 sun.misc.VM.addFinalRefCount(-1);
97 }
98 return r;
99 }
100 return null;
101 }
102
103 /**
104 * Polls this queue to see if a reference object is available. If one is
105 * available without further delay then it is removed from the queue and
106 * returned. Otherwise this method immediately returns <tt>null</tt>.
107 *
108 * @return A reference object, if one was immediately available,
109 * otherwise <code>null</code>
110 */
111 public Reference<? extends T> poll() {
112 if (head == null)
154 long end = System.nanoTime();
155 timeout -= (end - start) / 1000_000;
156 if (timeout <= 0) return null;
157 start = end;
158 }
159 }
160 }
161 }
162
163 /**
164 * Removes the next reference object in this queue, blocking until one
165 * becomes available.
166 *
167 * @return A reference object, blocking until one becomes available
168 * @throws InterruptedException If the wait is interrupted
169 */
170 public Reference<? extends T> remove() throws InterruptedException {
171 return remove(0);
172 }
173
174 /**
175 * Iterate queue and invoke given action with each Reference.
176 * Suitable for diagnostic purposes.
177 * WARNING: any use of this method should make sure to not
178 * retain the referents of iterated references (in case of
179 * FinalReference(s)) so that their life is not prolonged more
180 * than necessary.
181 */
182 void forEach(Consumer<? super Reference<? extends T>> action) {
183 for (Reference<? extends T> r = head; r != null;) {
184 action.accept(r);
185 Reference rn = r.next;
186 // make sure load of r.queue below doesn't float up before
187 // the load of r.next above. The corresponding stores are
188 // performed in reallyPoll() in reverse order.
189 U.loadFence();
190 if (rn == r) {
191 if (r.queue == ENQUEUED) {
192 // still enqueued -> we reached end of chain
193 r = null;
194 } else {
195 // already dequeued: r.queue == NULL; ->
196 // restart from head when overtaken by queue poller(s)
197 r = head;
198 }
199 } else {
200 // next in chain
201 r = rn;
202 }
203 }
204 }
205
206 /* we need a fence */
207 private static final Unsafe U = Unsafe.getUnsafe();
208 }
|