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/*
* Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package java.lang;
import jdk.internal.misc.VM;
/**
* Package-private utility class containing data structures and logic
* governing the virtual-machine shutdown sequence.
*
* @author Mark Reinhold
* @since 1.3
*
* @see java.io.Console
* @see ApplicationShutdownHooks
* @see java.io.DeleteOnExitHook
*/
class Shutdown {
// The system shutdown hooks are registered with a predefined slot.
// The list of shutdown hooks is as follows:
// (0) Console restore hook
// (1) ApplicationShutdownHooks that invokes all registered application
// shutdown hooks and waits until they finish
// (2) DeleteOnExit hook
private static final int MAX_SYSTEM_HOOKS = 10;
private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];
// the index of the currently running shutdown hook to the hooks array
private static int currentRunningHook = -1;
/* The preceding static fields are protected by this lock */
private static class Lock { };
private static Object lock = new Lock();
/* Lock object for the native halt method */
private static Object haltLock = new Lock();
/**
* Add a new system shutdown hook. Checks the shutdown state and
* the hook itself, but does not do any security checks.
*
* The registerShutdownInProgress parameter should be false except
* registering the DeleteOnExitHook since the first file may
* be added to the delete on exit list by the application shutdown
* hooks.
*
* @params slot the slot in the shutdown hook array, whose element
* will be invoked in order during shutdown
* @params registerShutdownInProgress true to allow the hook
* to be registered even if the shutdown is in progress.
* @params hook the hook to be registered
*
* @throws IllegalStateException
* if registerShutdownInProgress is false and shutdown is in progress; or
* if registerShutdownInProgress is true and the shutdown process
* already passes the given slot
*/
static void add(int slot, boolean registerShutdownInProgress, Runnable hook) {
if (slot < 0 || slot >= MAX_SYSTEM_HOOKS) {
throw new IllegalArgumentException("Invalid slot: " + slot);
}
synchronized (lock) {
if (hooks[slot] != null)
throw new InternalError("Shutdown hook at slot " + slot + " already registered");
if (!registerShutdownInProgress) {
if (currentRunningHook >= 0)
throw new IllegalStateException("Shutdown in progress");
} else {
if (VM.isShutdown() || slot <= currentRunningHook)
throw new IllegalStateException("Shutdown in progress");
}
hooks[slot] = hook;
}
}
/* Run all system shutdown hooks.
*
* The system shutdown hooks are run in the thread synchronized on
* Shutdown.class. Other threads calling Runtime::exit, Runtime::halt
* or JNI DestroyJavaVM will block indefinitely.
*
* ApplicationShutdownHooks is registered as one single hook that starts
* all application shutdown hooks and waits until they finish.
*/
private static void runHooks() {
synchronized (lock) {
/* Guard against the possibility of a daemon thread invoking exit
* after DestroyJavaVM initiates the shutdown sequence
*/
if (VM.isShutdown()) return;
}
for (int i=0; i < MAX_SYSTEM_HOOKS; i++) {
try {
Runnable hook;
synchronized (lock) {
// acquire the lock to make sure the hook registered during
// shutdown is visible here.
currentRunningHook = i;
hook = hooks[i];
}
if (hook != null) hook.run();
} catch (Throwable t) {
if (t instanceof ThreadDeath) {
ThreadDeath td = (ThreadDeath)t;
throw td;
}
}
}
// set shutdown state
VM.shutdown();
}
/* Notify the VM that it's time to halt. */
static native void beforeHalt();
/* The halt method is synchronized on the halt lock
* to avoid corruption of the delete-on-shutdown file list.
* It invokes the true native halt method.
*/
static void halt(int status) {
synchronized (haltLock) {
halt0(status);
}
}
static native void halt0(int status);
/* Invoked by Runtime.exit, which does all the security checks.
* Also invoked by handlers for system-provided termination events,
* which should pass a nonzero status code.
*/
static void exit(int status) {
synchronized (lock) {
if (status != 0 && VM.isShutdown()) {
/* Halt immediately on nonzero status */
halt(status);
}
}
synchronized (Shutdown.class) {
/* Synchronize on the class object, causing any other thread
* that attempts to initiate shutdown to stall indefinitely
*/
beforeHalt();
runHooks();
halt(status);
}
}
/* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
* thread has finished. Unlike the exit method, this method does not
* actually halt the VM.
*/
static void shutdown() {
synchronized (Shutdown.class) {
runHooks();
}
}
}