1 /*
2 * Copyright 2017 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.util.internal;
17
18 import io.netty.util.concurrent.FastThreadLocalThread;
19
20 import java.lang.ref.ReferenceQueue;
21 import java.lang.ref.WeakReference;
22 import java.security.AccessController;
23 import java.security.PrivilegedAction;
24 import java.util.Set;
25 import java.util.concurrent.atomic.AtomicBoolean;
26
27 import static io.netty.util.internal.SystemPropertyUtil.getInt;
28 import static java.lang.Math.max;
29
30 /**
31 * Allows a way to register some {@link Runnable} that will executed once there are no references to an {@link Object}
32 * anymore.
33 *
34 * @deprecated The object cleaner is deprecated for removal.
35 */
36 @Deprecated
37 public final class ObjectCleaner {
38 private static final int REFERENCE_QUEUE_POLL_TIMEOUT_MS =
39 max(500, getInt("io.netty.util.internal.ObjectCleaner.refQueuePollTimeout", 10000));
40
41 // Package-private for testing
42 static final String CLEANER_THREAD_NAME = ObjectCleaner.class.getSimpleName() + "Thread";
43 // This will hold a reference to the AutomaticCleanerReference which will be removed once we called cleanup()
44 private static final Set<AutomaticCleanerReference> LIVE_SET = new ConcurrentSet<AutomaticCleanerReference>();
45 private static final ReferenceQueue<Object> REFERENCE_QUEUE = new ReferenceQueue<Object>();
46 private static final AtomicBoolean CLEANER_RUNNING = new AtomicBoolean(false);
47 private static final Runnable CLEANER_TASK = new Runnable() {
48 @Override
49 public void run() {
50 boolean interrupted = false;
51 for (;;) {
52 // Keep on processing as long as the LIVE_SET is not empty and once it becomes empty
53 // See if we can let this thread complete.
54 while (!LIVE_SET.isEmpty()) {
55 final AutomaticCleanerReference reference;
56 try {
57 reference = (AutomaticCleanerReference) REFERENCE_QUEUE.remove(REFERENCE_QUEUE_POLL_TIMEOUT_MS);
58 } catch (InterruptedException ex) {
59 // Just consume and move on
60 interrupted = true;
61 continue;
62 }
63 if (reference != null) {
64 try {
65 reference.cleanup();
66 } catch (Throwable ignored) {
67 // ignore exceptions, and don't log in case the logger throws an exception, blocks, or has
68 // other unexpected side effects.
69 }
70 LIVE_SET.remove(reference);
71 }
72 }
73 CLEANER_RUNNING.set(false);
74
75 // Its important to first access the LIVE_SET and then CLEANER_RUNNING to ensure correct
76 // behavior in multi-threaded environments.
77 if (LIVE_SET.isEmpty() || !CLEANER_RUNNING.compareAndSet(false, true)) {
78 // There was nothing added after we set STARTED to false or some other cleanup Thread
79 // was started already so its safe to let this Thread complete now.
80 break;
81 }
82 }
83 if (interrupted) {
84 // As we caught the InterruptedException above we should mark the Thread as interrupted.
85 Thread.currentThread().interrupt();
86 }
87 }
88 };
89
90 /**
91 * Register the given {@link Object} for which the {@link Runnable} will be executed once there are no references
92 * to the object anymore.
93 *
94 * This should only be used if there are no other ways to execute some cleanup once the Object is not reachable
95 * anymore because it is not a cheap way to handle the cleanup.
96 */
97 public static void register(Object object, Runnable cleanupTask) {
98 AutomaticCleanerReference reference = new AutomaticCleanerReference(object,
99 ObjectUtil.checkNotNull(cleanupTask, "cleanupTask"));
100 // Its important to add the reference to the LIVE_SET before we access CLEANER_RUNNING to ensure correct
101 // behavior in multi-threaded environments.
102 LIVE_SET.add(reference);
103
104 // Check if there is already a cleaner running.
105 if (CLEANER_RUNNING.compareAndSet(false, true)) {
106 final Thread cleanupThread = new FastThreadLocalThread(CLEANER_TASK);
107 cleanupThread.setPriority(Thread.MIN_PRIORITY);
108 // Set to null to ensure we not create classloader leaks by holding a strong reference to the inherited
109 // classloader.
110 // See:
111 // - https://github.com/netty/netty/issues/7290
112 // - https://bugs.openjdk.java.net/browse/JDK-7008595
113 AccessController.doPrivileged(new PrivilegedAction<Void>() {
114 @Override
115 public Void run() {
116 cleanupThread.setContextClassLoader(null);
117 return null;
118 }
119 });
120 cleanupThread.setName(CLEANER_THREAD_NAME);
121
122 // Mark this as a daemon thread to ensure that we the JVM can exit if this is the only thread that is
123 // running.
124 cleanupThread.setDaemon(true);
125 cleanupThread.start();
126 }
127 }
128
129 public static int getLiveSetCount() {
130 return LIVE_SET.size();
131 }
132
133 private ObjectCleaner() {
134 // Only contains a static method.
135 }
136
137 private static final class AutomaticCleanerReference extends WeakReference<Object> {
138 private final Runnable cleanupTask;
139
140 AutomaticCleanerReference(Object referent, Runnable cleanupTask) {
141 super(referent, REFERENCE_QUEUE);
142 this.cleanupTask = cleanupTask;
143 }
144
145 void cleanup() {
146 cleanupTask.run();
147 }
148
149 @Override
150 public Thread get() {
151 return null;
152 }
153
154 @Override
155 public void clear() {
156 LIVE_SET.remove(this);
157 super.clear();
158 }
159 }
160 }