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
31
32 final class Finalizer extends FinalReference<Object> { /* Package-private; must be in
33 same package as the Reference
34 class */
35
36 /* A native method that invokes an arbitrary object's finalize method is
37 required since the finalize method is protected
38 */
39 static native void invokeFinalizeMethod(Object o) throws Throwable;
40
41 private static ReferenceQueue<Object> queue = new ReferenceQueue<>();
42 private static Finalizer unfinalized = null;
43 private static final Object lock = new Object();
44
45 private Finalizer
46 next = null,
47 prev = null;
48
49 private boolean hasBeenFinalized() {
50 return (next == this);
51 }
52
53 private void add() {
54 synchronized (lock) {
55 if (unfinalized != null) {
56 this.next = unfinalized;
57 unfinalized.prev = this;
58 }
59 unfinalized = this;
60 }
61 }
62
63 private void remove() {
64 synchronized (lock) {
65 if (unfinalized == this) {
66 if (this.next != null) {
67 unfinalized = this.next;
68 } else {
69 unfinalized = this.prev;
70 }
71 }
72 if (this.next != null) {
73 this.next.prev = this.prev;
74 }
75 if (this.prev != null) {
76 this.prev.next = this.next;
77 }
78 this.next = this; /* Indicates that this has been finalized */
79 this.prev = this;
80 }
81 }
82
83 private Finalizer(Object finalizee) {
84 super(finalizee, queue);
85 add();
86 }
87
88 /* Invoked by VM */
89 static void register(Object finalizee) {
90 new Finalizer(finalizee);
91 }
92
93 private void runFinalizer() {
94 synchronized (this) {
95 if (hasBeenFinalized()) return;
96 remove();
97 }
98 try {
99 Object finalizee = this.get();
100 if (finalizee != null && !(finalizee instanceof java.lang.Enum)) {
101 invokeFinalizeMethod(finalizee);
102 /* Clear stack slot containing this variable, to decrease
103 the chances of false retention with a conservative GC */
104 finalizee = null;
105 }
106 } catch (Throwable x) { }
107 super.clear();
108 }
109
110 /* Create a privileged secondary finalizer thread in the system thread
111 group for the given Runnable, and wait for it to complete.
112
113 This method is used by both runFinalization and runFinalizersOnExit.
114 The former method invokes all pending finalizers, while the latter
115 invokes all uninvoked finalizers if on-exit finalization has been
116 enabled.
117
118 These two methods could have been implemented by offloading their work
119 to the regular finalizer thread and waiting for that thread to finish.
120 The advantage of creating a fresh thread, however, is that it insulates
121 invokers of these methods from a stalled or deadlocked finalizer thread.
122 */
123 private static void forkSecondaryFinalizer(final Runnable proc) {
124 AccessController.doPrivileged(
125 new PrivilegedAction<Void>() {
126 public Void run() {
127 ThreadGroup tg = Thread.currentThread().getThreadGroup();
128 for (ThreadGroup tgn = tg;
129 tgn != null;
130 tg = tgn, tgn = tg.getParent());
131 Thread sft = new Thread(tg, proc, "Secondary finalizer");
132 sft.start();
133 try {
134 sft.join();
135 } catch (InterruptedException x) {
136 /* Ignore */
137 }
138 return null;
139 }});
140 }
141
142 /* Called by Runtime.runFinalization() */
143 static void runFinalization() {
144 forkSecondaryFinalizer(new Runnable() {
145 private volatile boolean running;
146 public void run() {
147 if (running)
148 return;
149 running = true;
150 for (;;) {
151 Finalizer f = (Finalizer)queue.poll();
152 if (f == null) break;
153 f.runFinalizer();
154 }
155 }
156 });
157 }
158
159 /* Invoked by java.lang.Shutdown */
160 static void runAllFinalizers() {
161 forkSecondaryFinalizer(new Runnable() {
162 private volatile boolean running;
163 public void run() {
164 if (running)
165 return;
166 running = true;
167 for (;;) {
168 Finalizer f;
169 synchronized (lock) {
170 f = unfinalized;
171 if (f == null) break;
172 unfinalized = f.next;
173 }
174 f.runFinalizer();
175 }}});
176 }
177
178 private static class FinalizerThread extends Thread {
179 private volatile boolean running;
180 FinalizerThread(ThreadGroup g) {
181 super(g, "Finalizer");
182 }
183 public void run() {
184 if (running)
185 return;
186 running = true;
187 for (;;) {
188 try {
189 Finalizer f = (Finalizer)queue.remove();
190 f.runFinalizer();
191 } catch (InterruptedException x) {
192 continue;
193 }
194 }
195 }
196 }
197
198 static {
199 ThreadGroup tg = Thread.currentThread().getThreadGroup();
200 for (ThreadGroup tgn = tg;
201 tgn != null;
202 tg = tgn, tgn = tg.getParent());
203 Thread finalizer = new FinalizerThread(tg);
204 finalizer.setPriority(Thread.MAX_PRIORITY - 2);
205 finalizer.setDaemon(true);
206 finalizer.start();
207 }
208
209 }