1 /* 2 * Copyright (c) 1999, 2005, 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 * @throw 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 /* The halt method is synchronized on the halt lock 134 * to avoid corruption of the delete-on-shutdown file list. 135 * It invokes the true native halt method. 136 */ 137 static void halt(int status) { 138 synchronized (haltLock) { 139 halt0(status); 140 } 141 } 142 143 static native void halt0(int status); 144 145 /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */ 146 private static native void runAllFinalizers(); 147 148 149 /* The actual shutdown sequence is defined here. 150 * 151 * If it weren't for runFinalizersOnExit, this would be simple -- we'd just 152 * run the hooks and then halt. Instead we need to keep track of whether 153 * we're running hooks or finalizers. In the latter case a finalizer could 154 * invoke exit(1) to cause immediate termination, while in the former case 155 * any further invocations of exit(n), for any n, simply stall. Note that 156 * if on-exit finalizers are enabled they're run iff the shutdown is 157 * initiated by an exit(0); they're never run on exit(n) for n != 0 or in 158 * response to SIGINT, SIGTERM, etc. 159 */ 160 private static void sequence() { 161 synchronized (lock) { 162 /* Guard against the possibility of a daemon thread invoking exit 163 * after DestroyJavaVM initiates the shutdown sequence 164 */ 165 if (state != HOOKS) return; 166 } 167 runHooks(); 168 boolean rfoe; 169 synchronized (lock) { 170 state = FINALIZERS; 171 rfoe = runFinalizersOnExit; 172 } 173 if (rfoe) runAllFinalizers(); 174 } 175 176 177 /* Invoked by Runtime.exit, which does all the security checks. 178 * Also invoked by handlers for system-provided termination events, 179 * which should pass a nonzero status code. 180 */ 181 static void exit(int status) { 182 boolean runMoreFinalizers = false; 183 synchronized (lock) { 184 if (status != 0) runFinalizersOnExit = false; 185 switch (state) { 186 case RUNNING: /* Initiate shutdown */ 187 state = HOOKS; 188 break; 189 case HOOKS: /* Stall and halt */ 190 break; 191 case FINALIZERS: 192 if (status != 0) { 193 /* Halt immediately on nonzero status */ 194 halt(status); 195 } else { 196 /* Compatibility with old behavior: 197 * Run more finalizers and then halt 198 */ 199 runMoreFinalizers = runFinalizersOnExit; 200 } 201 break; 202 } 203 } 204 if (runMoreFinalizers) { 205 runAllFinalizers(); 206 halt(status); 207 } 208 synchronized (Shutdown.class) { 209 /* Synchronize on the class object, causing any other thread 210 * that attempts to initiate shutdown to stall indefinitely 211 */ 212 sequence(); 213 halt(status); 214 } 215 } 216 217 218 /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon 219 * thread has finished. Unlike the exit method, this method does not 220 * actually halt the VM. 221 */ 222 static void shutdown() { 223 synchronized (lock) { 224 switch (state) { 225 case RUNNING: /* Initiate shutdown */ 226 state = HOOKS; 227 break; 228 case HOOKS: /* Stall and then return */ 229 case FINALIZERS: 230 break; 231 } 232 } 233 synchronized (Shutdown.class) { 234 sequence(); 235 } 236 } 237 238 }