/*
 * 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();
 }
 }

}