1 /*
2 * junixsocket
3 *
4 * Copyright 2009-2024 Christian Kohlschütter
5 *
6 * Licensed under the Apache License, Version 2.0 (the "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.newsclub.net.unix.rmi;
19
20 import java.lang.ref.WeakReference;
21 import java.util.ArrayList;
22 import java.util.List;
23
24 import com.kohlschutter.annotations.compiletime.SuppressFBWarnings;
25
26 /**
27 * Simplifies handling shutdown hooks.
28 *
29 * @author Christian Kohlschütter
30 */
31 final class ShutdownHookSupport {
32 private static final List<Thread> HOOKS = ("true".equals(System.getProperty(
33 "org.newsclub.net.unix.rmi.collect-shutdown-hooks", "false"))) ? new ArrayList<>() : null;
34
35 /**
36 * Registers a shutdown hook to be executed upon Runtime shutdown.
37 *
38 * NOTE: Only a weak reference to the hook is stored.
39 *
40 * @param hook The hook to register.
41 * @return The thread, to be used with #removeShutdownHook
42 */
43 public static Thread addWeakShutdownHook(ShutdownHook hook) {
44 Thread t = new ShutdownThread(new WeakReference<>(hook));
45 Runtime.getRuntime().addShutdownHook(t);
46 if (HOOKS != null) {
47 synchronized (HOOKS) {
48 HOOKS.add(t);
49 }
50 }
51 return t;
52 }
53
54 // only for unit testing
55 @SuppressFBWarnings({"RU_INVOKE_RUN"})
56 @SuppressWarnings("DoNotCall" /* errorprone */)
57 static void runHooks() {
58 if (HOOKS != null) {
59 List<Thread> list;
60 synchronized (HOOKS) {
61 list = new ArrayList<>(HOOKS);
62 HOOKS.clear();
63 }
64 for (Thread t : list) {
65 t.run(); // NOPMD -- code coverage fails if we call .start()
66 }
67 }
68 }
69
70 /**
71 * Something that wants to be called upon Runtime shutdown.
72 *
73 * @author Christian Kohlschütter
74 */
75 interface ShutdownHook {
76 /**
77 * Called upon Runtime shutdown.
78 *
79 * When you implement this method, make sure to check that the given Thread matches the current
80 * thread, e.g.: <code>
81 * if (thread != Thread.currentThread() || !(thread instanceof ShutdownThread)) {
82 * throw new IllegalStateException("Illegal caller"); }
83 * </code>
84 *
85 * @param thread The current Thread.
86 * @throws Exception Most likely ignored
87 */
88 @SuppressFBWarnings("THROWS_METHOD_THROWS_CLAUSE_BASIC_EXCEPTION")
89 void onRuntimeShutdown(Thread thread) throws Exception;
90 }
91
92 /**
93 * The Thread that will be called upon Runtime shutdown.
94 *
95 * @author Christian Kohlschütter
96 */
97 static final class ShutdownThread extends Thread {
98 private final WeakReference<ShutdownHook> ref;
99
100 ShutdownThread(WeakReference<ShutdownHook> ref) {
101 super();
102 this.ref = ref;
103 }
104
105 @Override
106 public void run() {
107 ShutdownHook hook = ref.get();
108 ref.clear();
109 try {
110 if (hook != null) {
111 hook.onRuntimeShutdown(this);
112 }
113 } catch (Exception e) {
114 // ignore
115 }
116 }
117 }
118 }