1 /*
2 * junixsocket
3 *
4 * Copyright 2009-2026 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 = newShutdownThread(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 @FunctionalInterface
76 interface ShutdownHook {
77 /**
78 * Called upon Runtime shutdown.
79 *
80 * When you implement this method, make sure to check that the given Thread matches the current
81 * thread, e.g.: <code>
82 * if (thread != Thread.currentThread()) {
83 * throw new IllegalStateException("Illegal caller"); }
84 * </code>
85 *
86 * @param thread The current Thread.
87 * @throws Exception Most likely ignored
88 */
89 @SuppressFBWarnings("THROWS_METHOD_THROWS_CLAUSE_BASIC_EXCEPTION")
90 void onRuntimeShutdown(Thread thread) throws Exception;
91 }
92
93 /**
94 * Create a Thread that will be called upon Runtime shutdown.
95 *
96 * @param ref The shutdown hook (weak reference).
97 */
98 public static Thread newShutdownThread(WeakReference<ShutdownHook> ref) {
99 return new Thread(() -> {
100 ShutdownHook hook = ref.get();
101 ref.clear();
102 try {
103 if (hook != null) {
104 hook.onRuntimeShutdown(Thread.currentThread());
105 }
106 } catch (Exception e) {
107 // ignore
108 }
109 }, "ShutdownHook");
110 }
111 }