1 /*
2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
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.security.PrivilegedAction;
29 import java.security.AccessController;
30 import sun.misc.JavaLangAccess;
31 import sun.misc.SharedSecrets;
32 import sun.misc.VM;
33
34 final class Finalizer extends FinalReference<Object> { /* Package-private; must be in
35 same package as the Reference
36 class */
37
38 private static ReferenceQueue<Object> queue = new ReferenceQueue<>();
39 private static Finalizer unfinalized = null;
40 private static final Object lock = new Object();
41
42 private Finalizer
43 next = null,
44 prev = null;
45
46 private boolean hasBeenFinalized() {
47 return (next == this);
48 }
49
50 private void add() {
51 synchronized (lock) {
52 if (unfinalized != null) {
53 this.next = unfinalized;
54 unfinalized.prev = this;
55 }
56 unfinalized = this;
57 }
58 }
59
60 private void remove() {
61 synchronized (lock) {
62 if (unfinalized == this) {
63 if (this.next != null) {
64 unfinalized = this.next;
65 } else {
66 unfinalized = this.prev;
67 }
68 }
69 if (this.next != null) {
70 this.next.prev = this.prev;
71 }
72 if (this.prev != null) {
73 this.prev.next = this.next;
74 }
75 this.next = this; /* Indicates that this has been finalized */
76 this.prev = this;
77 }
78 }
79
80 private Finalizer(Object finalizee) {
81 super(finalizee, queue);
82 add();
83 }
84
85 /* Invoked by VM */
86 static void register(Object finalizee) {
87 new Finalizer(finalizee);
88 }
89
90 private void runFinalizer(JavaLangAccess jla) {
91 synchronized (this) {
92 if (hasBeenFinalized()) return;
93 remove();
94 }
95 try {
96 Object finalizee = this.get();
97 if (finalizee != null && !(finalizee instanceof java.lang.Enum)) {
98 jla.invokeFinalize(finalizee);
99
100 /* Clear stack slot containing this variable, to decrease
101 the chances of false retention with a conservative GC */
102 finalizee = null;
103 }
104 } catch (Throwable x) { }
105 super.clear();
106 }
107
108 /* Create a privileged secondary finalizer thread in the system thread
109 group for the given Runnable, and wait for it to complete.
110
111 This method is used by both runFinalization and runFinalizersOnExit.
112 The former method invokes all pending finalizers, while the latter
113 invokes all uninvoked finalizers if on-exit finalization has been
114 enabled.
115
116 These two methods could have been implemented by offloading their work
117 to the regular finalizer thread and waiting for that thread to finish.
118 The advantage of creating a fresh thread, however, is that it insulates
119 invokers of these methods from a stalled or deadlocked finalizer thread.
120 */
121 private static void forkSecondaryFinalizer(final Runnable proc) {
122 AccessController.doPrivileged(
123 new PrivilegedAction<Void>() {
124 public Void run() {
125 ThreadGroup tg = Thread.currentThread().getThreadGroup();
126 for (ThreadGroup tgn = tg;
127 tgn != null;
128 tg = tgn, tgn = tg.getParent());
129 Thread sft = new Thread(tg, proc, "Secondary finalizer");
130 sft.start();
131 try {
132 sft.join();
133 } catch (InterruptedException x) {
134 /* Ignore */
135 }
136 return null;
137 }});
138 }
139
140 /* Called by Runtime.runFinalization() */
141 static void runFinalization() {
142 if (!VM.isBooted()) {
143 return;
144 }
145
146 final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
147 forkSecondaryFinalizer(new Runnable() {
148 private volatile boolean running;
149 public void run() {
150 if (running)
151 return;
152 running = true;
153 for (;;) {
154 Finalizer f = (Finalizer)queue.poll();
155 if (f == null) break;
156 f.runFinalizer(jla);
157 }
158 }
159 });
160 }
161
162 /* Invoked by java.lang.Shutdown */
163 static void runAllFinalizers() {
164 if (!VM.isBooted()) {
165 return;
166 }
167
168 final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
169 forkSecondaryFinalizer(new Runnable() {
170 private volatile boolean running;
171 public void run() {
172 if (running)
173 return;
174 running = true;
175 for (;;) {
176 Finalizer f;
177 synchronized (lock) {
178 f = unfinalized;
179 if (f == null) break;
180 unfinalized = f.next;
181 }
182 f.runFinalizer(jla);
183 }}});
184 }
185
186 private static class FinalizerThread extends Thread {
187 private volatile boolean running;
188 FinalizerThread(ThreadGroup g) {
189 super(g, "Finalizer");
190 }
191 public void run() {
192 if (running)
193 return;
194
195 // Finalizer thread starts before System.initializeSystemClass
196 // is called. Wait until JavaLangAccess is available
197 while (!VM.isBooted()) {
198 // delay until VM completes initialization
199 try {
200 VM.awaitBooted();
201 } catch (InterruptedException x) {
202 // ignore and continue
203 }
204 }
205 final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
206 running = true;
207 for (;;) {
208 try {
209 Finalizer f = (Finalizer)queue.remove();
210 f.runFinalizer(jla);
211 } catch (InterruptedException x) {
212 // ignore and continue
213 }
214 }
215 }
216 }
217
218 static {
219 ThreadGroup tg = Thread.currentThread().getThreadGroup();
220 for (ThreadGroup tgn = tg;
221 tgn != null;
222 tg = tgn, tgn = tg.getParent());
223 Thread finalizer = new FinalizerThread(tg);
224 finalizer.setPriority(Thread.MAX_PRIORITY - 2);
225 finalizer.setDaemon(true);
226 finalizer.start();
227 }
228
229 }