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 import jdk.internal.misc.VM; 30 31 /** 32 * Package-private utility class containing data structures and logic 33 * governing the virtual-machine shutdown sequence. 34 * 35 * @author Mark Reinhold 36 * @since 1.3 37 * 38 * @see java.io.Console 39 * @see ApplicationShutdownHooks 40 * @see java.io.DeleteOnExitHook 41 */ 42 43 class Shutdown { 44 45 // The system shutdown hooks are registered with a predefined slot. 46 // The list of shutdown hooks is as follows: 47 // (0) Console restore hook 48 // (1) ApplicationShutdownHooks that invokes all registered application 49 // shutdown hooks and waits until they finish 50 // (2) DeleteOnExit hook 51 private static final int MAX_SYSTEM_HOOKS = 10; 52 private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS]; 53 54 // the index of the currently running shutdown hook to the hooks array 55 private static int currentRunningHook = -1; 56 57 /* The preceding static fields are protected by this lock */ 58 private static class Lock { }; 59 private static Object lock = new Lock(); 60 61 /* Lock object for the native halt method */ 62 private static Object haltLock = new Lock(); 63 64 /** 65 * Add a new system shutdown hook. Checks the shutdown state and 66 * the hook itself, but does not do any security checks. 67 * 68 * The registerShutdownInProgress parameter should be false except 69 * registering the DeleteOnExitHook since the first file may 70 * be added to the delete on exit list by the application shutdown 71 * hooks. 72 * 73 * @params slot the slot in the shutdown hook array, whose element 74 * will be invoked in order during shutdown 75 * @params registerShutdownInProgress true to allow the hook 76 * to be registered even if the shutdown is in progress. 77 * @params hook the hook to be registered 78 * 79 * @throws IllegalStateException 80 * if registerShutdownInProgress is false and shutdown is in progress; or 81 * if registerShutdownInProgress is true and the shutdown process 82 * already passes the given slot 83 */ 84 static void add(int slot, boolean registerShutdownInProgress, Runnable hook) { 85 if (slot < 0 || slot >= MAX_SYSTEM_HOOKS) { 86 throw new IllegalArgumentException("Invalid slot: " + slot); 87 } 88 synchronized (lock) { 89 if (hooks[slot] != null) 90 throw new InternalError("Shutdown hook at slot " + slot + " already registered"); 91 92 if (!registerShutdownInProgress) { 93 if (currentRunningHook >= 0) 94 throw new IllegalStateException("Shutdown in progress"); 95 } else { 96 if (VM.isShutdown() || slot <= currentRunningHook) 97 throw new IllegalStateException("Shutdown in progress"); 98 } 99 100 hooks[slot] = hook; 101 } 102 } 103 104 /* Run all system shutdown hooks. 105 * 106 * The system shutdown hooks are run in the thread synchronized on 107 * Shutdown.class. Other threads calling Runtime::exit, Runtime::halt 108 * or JNI DestroyJavaVM will block indefinitely. 109 * 110 * ApplicationShutdownHooks is registered as one single hook that starts 111 * all application shutdown hooks and waits until they finish. 112 */ 113 private static void runHooks() { 114 synchronized (lock) { 115 /* Guard against the possibility of a daemon thread invoking exit 116 * after DestroyJavaVM initiates the shutdown sequence 117 */ 118 if (VM.isShutdown()) return; 119 } 120 121 for (int i=0; i < MAX_SYSTEM_HOOKS; i++) { 122 try { 123 Runnable hook; 124 synchronized (lock) { 125 // acquire the lock to make sure the hook registered during 126 // shutdown is visible here. 127 currentRunningHook = i; 128 hook = hooks[i]; 129 } 130 if (hook != null) hook.run(); 131 } catch (Throwable t) { 132 if (t instanceof ThreadDeath) { 133 ThreadDeath td = (ThreadDeath)t; 134 throw td; 135 } 136 } 137 } 138 139 // set shutdown state 140 VM.shutdown(); 141 } 142 143 /* Notify the VM that it's time to halt. */ 144 static native void beforeHalt(); 145 146 /* The halt method is synchronized on the halt lock 147 * to avoid corruption of the delete-on-shutdown file list. 148 * It invokes the true native halt method. 149 */ 150 static void halt(int status) { 151 synchronized (haltLock) { 152 halt0(status); 153 } 154 } 155 156 static native void halt0(int status); 157 158 /* Invoked by Runtime.exit, which does all the security checks. 159 * Also invoked by handlers for system-provided termination events, 160 * which should pass a nonzero status code. 161 */ 162 static void exit(int status) { 163 synchronized (lock) { 164 if (status != 0 && VM.isShutdown()) { 165 /* Halt immediately on nonzero status */ 166 halt(status); 167 } 168 } 169 synchronized (Shutdown.class) { 170 /* Synchronize on the class object, causing any other thread 171 * that attempts to initiate shutdown to stall indefinitely 172 */ 173 beforeHalt(); 174 runHooks(); 175 halt(status); 176 } 177 } 178 179 180 /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon 181 * thread has finished. Unlike the exit method, this method does not 182 * actually halt the VM. 183 */ 184 static void shutdown() { 185 synchronized (Shutdown.class) { 186 runHooks(); 187 } 188 } 189 190 }