/*

 * Copyright (c) 2013, 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 sun.misc;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.ProtectionDomain;

import java.security.PrivilegedAction;

import java.util.concurrent.atomic.AtomicInteger;

/**

 * A thread that has no permissions, is not a member of any user-defined

 * ThreadGroup and supports the ability to erase ThreadLocals.

 *

 * @implNote Based on the implementation of InnocuousForkJoinWorkerThread.

 */

public final class InnocuousThread extends Thread {

    private static final Unsafe UNSAFE;

    private static final long THREAD_LOCALS;

    private static final long INHERITABLE_THREAD_LOCALS;

    private static final ThreadGroup INNOCUOUSTHREADGROUP;

    private static final AccessControlContext ACC;

    private static final long INHERITEDACCESSCONTROLCONTEXT;

    private static final long CONTEXTCLASSLOADER;

    private static final AtomicInteger threadNumber = new AtomicInteger(1);

    private static String newName() {

        return "InnocuousThread-" + threadNumber.getAndIncrement();

    }

    /**

     * Returns a new InnocuousThread with an auto-generated thread name.

     * Its context class loader is set to null.

     */

    public static Thread newSystemThread(Runnable target) {

        return newSystemThread(newName(), target);

    }

    /**

     * Returns a new InnocuousThread with null context class loader.

     */

    public static Thread newSystemThread(String name, Runnable target) {

        return new InnocuousThread(INNOCUOUSTHREADGROUP,

                                   target, name, null);

    }

    public InnocuousThread(Runnable target) {

        super(INNOCUOUSTHREADGROUP, target, newName());

        UNSAFE.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, ACC);

        eraseThreadLocals();

    }

    private InnocuousThread(ThreadGroup group, Runnable target, String name, ClassLoader tccl) {

        super(group, target, name, 0L);

        UNSAFE.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, ACC);

        UNSAFE.putOrderedObject(this, CONTEXTCLASSLOADER, tccl);

        eraseThreadLocals();

    }

    @Override

    public ClassLoader getContextClassLoader() {

        // always report system class loader

        return ClassLoader.getSystemClassLoader();

    }

    @Override

    public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) {

        // silently fail

    }

    @Override

    public void setContextClassLoader(ClassLoader cl) {

        throw new SecurityException("setContextClassLoader");

    }

    // ensure run method is run only once

    private volatile boolean hasRun;

    @Override

    public void run() {

        if (Thread.currentThread() == this && !hasRun) {

            hasRun = true;

            super.run();

        }

    }

    /**

     * Drops all thread locals (and inherited thread locals).

     */

    public void eraseThreadLocals() {

        UNSAFE.putObject(this, THREAD_LOCALS, null);

        UNSAFE.putObject(this, INHERITABLE_THREAD_LOCALS, null);

    }

    // Use Unsafe to access Thread group and ThreadGroup parent fields

    static {

        try {

            ACC = new AccessControlContext(new ProtectionDomain[] {

                new ProtectionDomain(null, null)

            });

            // Find and use topmost ThreadGroup as parent of new group

            UNSAFE = Unsafe.getUnsafe();

            Class<?> tk = Thread.class;

            Class<?> gk = ThreadGroup.class;

            THREAD_LOCALS = UNSAFE.objectFieldOffset

                (tk.getDeclaredField("threadLocals"));

            INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset

                (tk.getDeclaredField("inheritableThreadLocals"));

            INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset

                (tk.getDeclaredField("inheritedAccessControlContext"));

            CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset

                (tk.getDeclaredField("contextClassLoader"));

            long tg = UNSAFE.objectFieldOffset(tk.getDeclaredField("group"));

            long gp = UNSAFE.objectFieldOffset(gk.getDeclaredField("parent"));

            ThreadGroup group = (ThreadGroup)

                UNSAFE.getObject(Thread.currentThread(), tg);

            while (group != null) {

                ThreadGroup parent = (ThreadGroup)UNSAFE.getObject(group, gp);

                if (parent == null)

                    break;

                group = parent;

            }

            final ThreadGroup root = group;

            INNOCUOUSTHREADGROUP = AccessController.doPrivileged(

                new PrivilegedAction<ThreadGroup>() {

                    @Override

                    public ThreadGroup run() {

                        return new ThreadGroup(root, "InnocuousThreadGroup");

                    }

                });

        } catch (Exception e) {

            throw new Error(e);

        }

    }

}