/*
 * Copyright (c) 1997, 2015, 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.ref;

import java.security.PrivilegedAction;
import java.security.AccessController;
import jdk.internal.misc.JavaLangAccess;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.misc.VM;

final class Finalizer extends FinalReference<Object> { /* Package-private; must be in
                                                          same package as the Reference
                                                          class */

    private static ReferenceQueue<Object> queue = new ReferenceQueue<>();

    /** Head of doubly linked list of Finalizers awaiting finalization. */
    private static Finalizer unfinalized = null;

    /** Lock guarding access to unfinalized list. */
    private static final Object lock = new Object();

    private Finalizer next, prev;

    private Finalizer(Object finalizee) {
        super(finalizee, queue);
        // push onto unfinalized
        synchronized (lock) {
            if (unfinalized != null) {
                this.next = unfinalized;
                unfinalized.prev = this;
            }
            unfinalized = this;
        }
    }

    static ReferenceQueue<Object> getQueue() {
        return queue;
    }

    /* Invoked by VM */
    static void register(Object finalizee) {
        new Finalizer(finalizee);
    }

    private void deregisterAndRunFinalizer(JavaLangAccess jla) {
        synchronized (lock) {
            if (this.next == this)      // already finalized
                return;
            // unlink from unfinalized
            if (unfinalized == this)
                unfinalized = this.next;
            else
                this.prev.next = this.next;
            if (this.next != null)
                this.next.prev = this.prev;
            this.prev = null;
            this.next = this;           // mark as finalized
        }
        runFinalizer(jla);
    }

    private void runFinalizer(JavaLangAccess jla) {
        try {
            Object finalizee = this.get();
            if (finalizee != null && !(finalizee instanceof java.lang.Enum)) {
                jla.invokeFinalize(finalizee);

                /* Clear stack slot containing this variable, to decrease
                   the chances of false retention with a conservative GC */
                finalizee = null;
            }
        } catch (Throwable x) { }
        super.clear();
    }

    /* Create a privileged secondary finalizer thread in the system thread
       group for the given Runnable, and wait for it to complete.

       This method is used by both runFinalization and runFinalizersOnExit.
       The former method invokes all pending finalizers, while the latter
       invokes all uninvoked finalizers if on-exit finalization has been
       enabled.

       These two methods could have been implemented by offloading their work
       to the regular finalizer thread and waiting for that thread to finish.
       The advantage of creating a fresh thread, however, is that it insulates
       invokers of these methods from a stalled or deadlocked finalizer thread.
     */
    private static void forkSecondaryFinalizer(final Runnable proc) {
        AccessController.doPrivileged(
            new PrivilegedAction<>() {
                public Void run() {
                    ThreadGroup tg = Thread.currentThread().getThreadGroup();
                    for (ThreadGroup tgn = tg;
                         tgn != null;
                         tg = tgn, tgn = tg.getParent());
                    Thread sft = new Thread(tg, proc, "Secondary finalizer", 0, false);
                    sft.start();
                    try {
                        sft.join();
                    } catch (InterruptedException x) {
                        Thread.currentThread().interrupt();
                    }
                    return null;
                }});
    }

    /* Called by Runtime.runFinalization() */
    static void runFinalization() {
        if (VM.initLevel() == 0) {
            return;
        }

        forkSecondaryFinalizer(new Runnable() {
            private volatile boolean running;
            public void run() {
                // in case of recursive call to run()
                if (running)
                    return;
                final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
                running = true;
                for (Finalizer f; (f = (Finalizer)queue.poll()) != null; )
                    f.deregisterAndRunFinalizer(jla);
            }
        });
    }

    /* Invoked by java.lang.Shutdown */
    static void runAllFinalizers() {
        if (VM.initLevel() == 0) {
            return;
        }

        forkSecondaryFinalizer(new Runnable() {
            private volatile boolean running;
            public void run() {
                // in case of recursive call to run()
                if (running)
                    return;
                final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
                running = true;
                for (;;) {
                    // "pollFirst" from unfinalized
                    Finalizer f;
                    synchronized (lock) {
                        f = unfinalized;
                        if (f == null) break;
                        unfinalized = f.next;
                        if (unfinalized != null)
                            unfinalized.prev = null;
                        f.next = f; // mark as finalized
                    }
                    f.runFinalizer(jla);
                }}});
    }

    private static class FinalizerThread extends Thread {
        private volatile boolean running;
        FinalizerThread(ThreadGroup g) {
            super(g, null, "Finalizer", 0, false);
        }
        public void run() {
            // in case of recursive call to run()
            if (running)
                return;

            // Finalizer thread starts before System.initializeSystemClass
            // is called.  Wait until JavaLangAccess is available
            while (VM.initLevel() == 0) {
                // delay until VM completes initialization
                try {
                    VM.awaitInitLevel(1);
                } catch (InterruptedException x) {
                    // ignore and continue
                }
            }
            final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();
            running = true;
            for (;;) {
                try {
                    Finalizer f = (Finalizer)queue.remove();
                    f.deregisterAndRunFinalizer(jla);
                } catch (InterruptedException x) {
                    // ignore and continue
                }
            }
        }
    }

    static {
        ThreadGroup tg = Thread.currentThread().getThreadGroup();
        for (ThreadGroup tgn = tg;
             tgn != null;
             tg = tgn, tgn = tg.getParent());
        Thread finalizer = new FinalizerThread(tg);
        finalizer.setPriority(Thread.MAX_PRIORITY - 2);
        finalizer.setDaemon(true);
        finalizer.start();
    }

}