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.DontInline;
29 import jdk.internal.HotSpotIntrinsicCandidate;
30 import jdk.internal.misc.JavaLangRefAccess;
31 import jdk.internal.misc.SharedSecrets;
32 import jdk.internal.ref.Cleaner;
33
34 /**
35 * Abstract base class for reference objects. This class defines the
36 * operations common to all reference objects. Because reference objects are
37 * implemented in close cooperation with the garbage collector, this class may
38 * not be subclassed directly.
39 *
40 * @author Mark Reinhold
41 * @since 1.2
42 */
43
44 public abstract class Reference<T> {
45
46 /* A Reference instance is in one of four possible internal states:
47 *
48 * Active: Subject to special treatment by the garbage collector. Some
49 * time after the collector detects that the reachability of the
50 * referent has changed to the appropriate state, it changes the
51 * instance's state to either Pending or Inactive, depending upon
52 * whether or not the instance was registered with a queue when it was
122 /* List of References waiting to be enqueued. The collector adds
123 * References to this list, while the Reference-handler thread removes
124 * them. This list is protected by the above lock object. The
125 * list uses the discovered field to link its elements.
126 */
127 private static Reference<Object> pending = null;
128
129 /* High-priority thread to enqueue pending References
130 */
131 private static class ReferenceHandler extends Thread {
132
133 private static void ensureClassInitialized(Class<?> clazz) {
134 try {
135 Class.forName(clazz.getName(), true, clazz.getClassLoader());
136 } catch (ClassNotFoundException e) {
137 throw (Error) new NoClassDefFoundError(e.getMessage()).initCause(e);
138 }
139 }
140
141 static {
142 // pre-load and initialize InterruptedException and Cleaner classes
143 // so that we don't get into trouble later in the run loop if there's
144 // memory shortage while loading/initializing them lazily.
145 ensureClassInitialized(InterruptedException.class);
146 ensureClassInitialized(Cleaner.class);
147 }
148
149 ReferenceHandler(ThreadGroup g, String name) {
150 super(g, null, name, 0, false);
151 }
152
153 public void run() {
154 while (true) {
155 tryHandlePending(true);
156 }
157 }
158 }
159
160 /**
161 * Try handle pending {@link Reference} if there is one.<p>
162 * Return {@code true} as a hint that there might be another
163 * {@link Reference} pending or {@code false} when there are no more pending
164 * {@link Reference}s at the moment and the program can do some other
165 * useful work instead of looping.
166 *
167 * @param waitForNotify if {@code true} and there was no pending
168 * {@link Reference}, wait until notified from VM
169 * or interrupted; if {@code false}, return immediately
170 * when there is no pending {@link Reference}.
171 * @return {@code true} if there was a {@link Reference} pending and it
172 * was processed, or we waited for notification and either got it
173 * or thread was interrupted before being notified;
174 * {@code false} otherwise.
175 */
176 static boolean tryHandlePending(boolean waitForNotify) {
177 Reference<Object> r;
178 Cleaner c;
179 try {
180 synchronized (lock) {
181 if (pending != null) {
182 r = pending;
183 // 'instanceof' might throw OutOfMemoryError sometimes
184 // so do this before un-linking 'r' from the 'pending' chain...
185 c = r instanceof Cleaner ? (Cleaner) r : null;
186 // unlink 'r' from 'pending' chain
187 pending = r.discovered;
188 r.discovered = null;
189 } else {
190 // The waiting on the lock may cause an OutOfMemoryError
191 // because it may try to allocate exception objects.
192 if (waitForNotify) {
193 lock.wait();
194 }
195 // retry if waited
196 return waitForNotify;
197 }
198 }
199 } catch (OutOfMemoryError x) {
200 // Give other threads CPU time so they hopefully drop some live references
201 // and GC reclaims some space.
202 // Also prevent CPU intensive spinning in case 'r instanceof Cleaner' above
203 // persistently throws OOME for some time...
204 Thread.yield();
205 // retry
206 return true;
207 } catch (InterruptedException x) {
208 // retry
209 return true;
210 }
211
212 // Fast path for cleaners
213 if (c != null) {
214 c.clean();
215 return true;
216 }
217
218 ReferenceQueue<? super Object> q = r.queue;
219 if (q != ReferenceQueue.NULL) q.enqueue(r);
220 return true;
221 }
222
223 static {
224 ThreadGroup tg = Thread.currentThread().getThreadGroup();
225 for (ThreadGroup tgn = tg;
226 tgn != null;
227 tg = tgn, tgn = tg.getParent());
228 Thread handler = new ReferenceHandler(tg, "Reference Handler");
229 /* If there were a special system-only priority greater than
230 * MAX_PRIORITY, it would be used here
231 */
232 handler.setPriority(Thread.MAX_PRIORITY);
233 handler.setDaemon(true);
234 handler.start();
|
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.DontInline;
29 import jdk.internal.HotSpotIntrinsicCandidate;
30 import jdk.internal.misc.JavaLangRefAccess;
31 import jdk.internal.misc.SharedSecrets;
32
33 /**
34 * Abstract base class for reference objects. This class defines the
35 * operations common to all reference objects. Because reference objects are
36 * implemented in close cooperation with the garbage collector, this class may
37 * not be subclassed directly.
38 *
39 * @author Mark Reinhold
40 * @since 1.2
41 */
42
43 public abstract class Reference<T> {
44
45 /* A Reference instance is in one of four possible internal states:
46 *
47 * Active: Subject to special treatment by the garbage collector. Some
48 * time after the collector detects that the reachability of the
49 * referent has changed to the appropriate state, it changes the
50 * instance's state to either Pending or Inactive, depending upon
51 * whether or not the instance was registered with a queue when it was
121 /* List of References waiting to be enqueued. The collector adds
122 * References to this list, while the Reference-handler thread removes
123 * them. This list is protected by the above lock object. The
124 * list uses the discovered field to link its elements.
125 */
126 private static Reference<Object> pending = null;
127
128 /* High-priority thread to enqueue pending References
129 */
130 private static class ReferenceHandler extends Thread {
131
132 private static void ensureClassInitialized(Class<?> clazz) {
133 try {
134 Class.forName(clazz.getName(), true, clazz.getClassLoader());
135 } catch (ClassNotFoundException e) {
136 throw (Error) new NoClassDefFoundError(e.getMessage()).initCause(e);
137 }
138 }
139
140 static {
141 // pre-load and initialize InterruptedException class
142 // so that we don't get into trouble later in the run loop if there's
143 // memory shortage while loading/initializing it lazily.
144 ensureClassInitialized(InterruptedException.class);
145 }
146
147 ReferenceHandler(ThreadGroup g, String name) {
148 super(g, null, name, 0, false);
149 }
150
151 public void run() {
152 while (true) {
153 tryHandlePending(true);
154 }
155 }
156 }
157
158 /**
159 * Try handle pending {@link Reference} if there is one.<p>
160 * Return {@code true} as a hint that there might be another
161 * {@link Reference} pending or {@code false} when there are no more pending
162 * {@link Reference}s at the moment and the program can do some other
163 * useful work instead of looping.
164 *
165 * @param waitForNotify if {@code true} and there was no pending
166 * {@link Reference}, wait until notified from VM
167 * or interrupted; if {@code false}, return immediately
168 * when there is no pending {@link Reference}.
169 * @return {@code true} if there was a {@link Reference} pending and it
170 * was processed, or we waited for notification and either got it
171 * or thread was interrupted before being notified;
172 * {@code false} otherwise.
173 */
174 static boolean tryHandlePending(boolean waitForNotify) {
175 Reference<Object> r;
176 try {
177 synchronized (lock) {
178 r = pending;
179 if (r != null) {
180 // unlink 'r' from 'pending' chain
181 pending = r.discovered;
182 r.discovered = null;
183 } else {
184 // The waiting on the lock may cause an OutOfMemoryError
185 // because it may try to allocate exception objects.
186 if (waitForNotify) {
187 lock.wait();
188 }
189 // retry if waited
190 return waitForNotify;
191 }
192 }
193 } catch (OutOfMemoryError x) {
194 // Give other threads CPU time so they hopefully drop some live references
195 // and GC reclaims some space.
196 Thread.yield();
197 // retry
198 return true;
199 } catch (InterruptedException x) {
200 // retry
201 return true;
202 }
203
204 ReferenceQueue<? super Object> q = r.queue;
205 if (q != ReferenceQueue.NULL) q.enqueue(r);
206 return true;
207 }
208
209 static {
210 ThreadGroup tg = Thread.currentThread().getThreadGroup();
211 for (ThreadGroup tgn = tg;
212 tgn != null;
213 tg = tgn, tgn = tg.getParent());
214 Thread handler = new ReferenceHandler(tg, "Reference Handler");
215 /* If there were a special system-only priority greater than
216 * MAX_PRIORITY, it would be used here
217 */
218 handler.setPriority(Thread.MAX_PRIORITY);
219 handler.setDaemon(true);
220 handler.start();
|