/*

 * Copyright (c) 2005, 2010, 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 java.util.*;

/*

 * Class to track and run user level shutdown hooks registered through

 * <tt>{@link Runtime#addShutdownHook Runtime.addShutdownHook}</tt>.

 *

 * @see java.lang.Runtime#addShutdownHook

 * @see java.lang.Runtime#removeShutdownHook

 */

class ApplicationShutdownHooks {

    /* The set of registered hooks */

    private static IdentityHashMap<Thread, Thread> hooks;

    static {

        try {

            Shutdown.add(1 /* shutdown hook invocation order */,

                false /* not registered if shutdown in progress */,

                new Runnable() {

                    public void run() {

                        runHooks();

                    }

                }

            );

            hooks = new IdentityHashMap<>();

        } catch (IllegalStateException e) {

            // application shutdown hooks cannot be added if

            // shutdown is in progress.

            hooks = null;

        }

    }

    private ApplicationShutdownHooks() {}

    /* Add a new shutdown hook.  Checks the shutdown state and the hook itself,

     * but does not do any security checks.

     */

    static synchronized void add(Thread hook) {

        if(hooks == null)

            throw new IllegalStateException("Shutdown in progress");

        if (hook.isAlive())

            throw new IllegalArgumentException("Hook already running");

        if (hooks.containsKey(hook))

            throw new IllegalArgumentException("Hook previously registered");

        hooks.put(hook, hook);

    }

    /* Remove a previously-registered hook.  Like the add method, this method

     * does not do any security checks.

     */

    static synchronized boolean remove(Thread hook) {

        if(hooks == null)

            throw new IllegalStateException("Shutdown in progress");

        if (hook == null)

            throw new NullPointerException();

        return hooks.remove(hook) != null;

    }

    /* Iterates over all application hooks creating a new thread for each

     * to run in. Hooks are run concurrently and this method waits for

     * them to finish.

     */

    static void runHooks() {

        Collection<Thread> threads;

        synchronized(ApplicationShutdownHooks.class) {

            threads = hooks.keySet();

            hooks = null;

        }

        for (Thread hook : threads) {

            hook.start();

        }

        for (Thread hook : threads) {

            while (true) {

                try {

                    hook.join();

                    break;

                } catch (InterruptedException ignored) {

                }

            }

        }

    }

}