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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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	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();
	}
	}

	}

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