/*

 * 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();

        }

    }

}