1 /*
2 * Copyright (c) 1999, 2018, 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;
27
28
29 /**
30 * Package-private utility class containing data structures and logic
31 * governing the virtual-machine shutdown sequence.
32 *
33 * @author Mark Reinhold
34 * @since 1.3
35 */
36
37 class Shutdown {
38
39 /* Shutdown state */
40 private static final int RUNNING = 0;
41 private static final int HOOKS = 1;
42 private static final int FINALIZERS = 2;
43 private static int state = RUNNING;
44
45 /* Should we run all finalizers upon exit? */
46 private static boolean runFinalizersOnExit = false;
47
48 // The system shutdown hooks are registered with a predefined slot.
49 // The list of shutdown hooks is as follows:
50 // (0) Console restore hook
51 // (1) Application hooks
52 // (2) DeleteOnExit hook
53 private static final int MAX_SYSTEM_HOOKS = 10;
54 private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];
55
56 // the index of the currently running shutdown hook to the hooks array
57 private static int currentRunningHook = 0;
58
59 /* The preceding static fields are protected by this lock */
60 private static class Lock { };
61 private static Object lock = new Lock();
62
63 /* Lock object for the native halt method */
64 private static Object haltLock = new Lock();
65
66 /* Invoked by Runtime.runFinalizersOnExit */
67 static void setRunFinalizersOnExit(boolean run) {
68 synchronized (lock) {
69 runFinalizersOnExit = run;
70 }
71 }
72
73
74 /**
75 * Add a new shutdown hook. Checks the shutdown state and the hook itself,
76 * but does not do any security checks.
77 *
78 * The registerShutdownInProgress parameter should be false except
79 * registering the DeleteOnExitHook since the first file may
80 * be added to the delete on exit list by the application shutdown
81 * hooks.
82 *
83 * @params slot the slot in the shutdown hook array, whose element
84 * will be invoked in order during shutdown
85 * @params registerShutdownInProgress true to allow the hook
86 * to be registered even if the shutdown is in progress.
87 * @params hook the hook to be registered
88 *
89 * @throws IllegalStateException
90 * if registerShutdownInProgress is false and shutdown is in progress; or
91 * if registerShutdownInProgress is true and the shutdown process
92 * already passes the given slot
93 */
94 static void add(int slot, boolean registerShutdownInProgress, Runnable hook) {
95 synchronized (lock) {
96 if (hooks[slot] != null)
97 throw new InternalError("Shutdown hook at slot " + slot + " already registered");
98
99 if (!registerShutdownInProgress) {
100 if (state > RUNNING)
101 throw new IllegalStateException("Shutdown in progress");
102 } else {
103 if (state > HOOKS || (state == HOOKS && slot <= currentRunningHook))
104 throw new IllegalStateException("Shutdown in progress");
105 }
106
107 hooks[slot] = hook;
108 }
109 }
110
111 /* Run all registered shutdown hooks
112 */
113 private static void runHooks() {
114 for (int i=0; i < MAX_SYSTEM_HOOKS; i++) {
115 try {
116 Runnable hook;
117 synchronized (lock) {
118 // acquire the lock to make sure the hook registered during
119 // shutdown is visible here.
120 currentRunningHook = i;
121 hook = hooks[i];
122 }
123 if (hook != null) hook.run();
124 } catch(Throwable t) {
125 if (t instanceof ThreadDeath) {
126 ThreadDeath td = (ThreadDeath)t;
127 throw td;
128 }
129 }
130 }
131 }
132
133 /* Notify the VM that it's time to halt. */
134 static native void beforeHalt();
135
136 /* The halt method is synchronized on the halt lock
137 * to avoid corruption of the delete-on-shutdown file list.
138 * It invokes the true native halt method.
139 */
140 static void halt(int status) {
141 synchronized (haltLock) {
142 halt0(status);
143 }
144 }
145
146 static native void halt0(int status);
147
148 /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */
149 private static native void runAllFinalizers();
150
151
152 /* The actual shutdown sequence is defined here.
153 *
154 * If it weren't for runFinalizersOnExit, this would be simple -- we'd just
155 * run the hooks and then halt. Instead we need to keep track of whether
156 * we're running hooks or finalizers. In the latter case a finalizer could
157 * invoke exit(1) to cause immediate termination, while in the former case
158 * any further invocations of exit(n), for any n, simply stall. Note that
159 * if on-exit finalizers are enabled they're run iff the shutdown is
160 * initiated by an exit(0); they're never run on exit(n) for n != 0 or in
161 * response to SIGINT, SIGTERM, etc.
162 */
163 private static void sequence() {
164 synchronized (lock) {
165 /* Guard against the possibility of a daemon thread invoking exit
166 * after DestroyJavaVM initiates the shutdown sequence
167 */
168 if (state != HOOKS) return;
169 }
170 runHooks();
171 boolean rfoe;
172 synchronized (lock) {
173 state = FINALIZERS;
174 rfoe = runFinalizersOnExit;
175 }
176 if (rfoe) runAllFinalizers();
177 }
178
179
180 /* Invoked by Runtime.exit, which does all the security checks.
181 * Also invoked by handlers for system-provided termination events,
182 * which should pass a nonzero status code.
183 */
184 static void exit(int status) {
185 boolean runMoreFinalizers = false;
186 synchronized (lock) {
187 if (status != 0) runFinalizersOnExit = false;
188 switch (state) {
189 case RUNNING: /* Initiate shutdown */
190 state = HOOKS;
191 break;
192 case HOOKS: /* Stall and halt */
193 break;
194 case FINALIZERS:
195 if (status != 0) {
196 /* Halt immediately on nonzero status */
197 halt(status);
198 } else {
199 /* Compatibility with old behavior:
200 * Run more finalizers and then halt
201 */
202 runMoreFinalizers = runFinalizersOnExit;
203 }
204 break;
205 }
206 }
207 if (runMoreFinalizers) {
208 runAllFinalizers();
209 halt(status);
210 }
211 synchronized (Shutdown.class) {
212 /* Synchronize on the class object, causing any other thread
213 * that attempts to initiate shutdown to stall indefinitely
214 */
215 beforeHalt();
216 sequence();
217 halt(status);
218 }
219 }
220
221
222 /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
223 * thread has finished. Unlike the exit method, this method does not
224 * actually halt the VM.
225 */
226 static void shutdown() {
227 synchronized (lock) {
228 switch (state) {
229 case RUNNING: /* Initiate shutdown */
230 state = HOOKS;
231 break;
232 case HOOKS: /* Stall and then return */
233 case FINALIZERS:
234 break;
235 }
236 }
237 synchronized (Shutdown.class) {
238 sequence();
239 }
240 }
241
242 }