1 /*

     2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package jdk.internal.misc;

    27 

    28 import java.security.AccessControlContext;

    29 import java.security.AccessController;

    30 import java.security.ProtectionDomain;

    31 import java.security.PrivilegedAction;

    32 import java.util.concurrent.atomic.AtomicInteger;

    33 

    34 /**

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

    36  * ThreadGroup and supports the ability to erase ThreadLocals.

    37  */

    38 public final class InnocuousThread extends Thread {

    39     private static final jdk.internal.misc.Unsafe UNSAFE;

    40     private static final long THREAD_LOCALS;

    41     private static final long INHERITABLE_THREAD_LOCALS;

    42     private static final ThreadGroup INNOCUOUSTHREADGROUP;

    43     private static final AccessControlContext ACC;

    44     private static final long INHERITEDACCESSCONTROLCONTEXT;

    45     private static final long CONTEXTCLASSLOADER;

    46 

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

    48     private static String newName() {

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

    50     }

    51 

    52     /**

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

    54      * and its context class loader is set to the system class loader.

    55      */

    56     public static Thread newThread(Runnable target) {

    57         return newThread(newName(), target);

    58     }

    59 

    60     /**

    61      * Returns a new InnocuousThread with its context class loader

    62      * set to the system class loader.

    63      */

    64     public static Thread newThread(String name, Runnable target) {

    65         return new InnocuousThread(INNOCUOUSTHREADGROUP,

    66                                    target,

    67                                    name,

    68                                    ClassLoader.getSystemClassLoader());

    69     }

    70 

    71     /**

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

    73      * Its context class loader is set to null.

    74      */

    75     public static Thread newSystemThread(Runnable target) {

    76         return newSystemThread(newName(), target);

    77     }

    78 

    79     /**

    80      * Returns a new InnocuousThread with null context class loader.

    81      */

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

    83         return new InnocuousThread(INNOCUOUSTHREADGROUP,

    84                                    target, name, null);

    85     }

    86 

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

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

    89         UNSAFE.putObjectRelease(this, INHERITEDACCESSCONTROLCONTEXT, ACC);

    90         UNSAFE.putObjectRelease(this, CONTEXTCLASSLOADER, tccl);

    91     }

    92 

    93     @Override

    94     public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) {

    95         // silently fail

    96     }

    97 

    98     @Override

    99     public void setContextClassLoader(ClassLoader cl) {

   100         // Allow clearing of the TCCL to remove the reference to the system classloader.

   101         if (cl == null)

   102             super.setContextClassLoader(null);

   103         else

   104             throw new SecurityException("setContextClassLoader");

   105     }

   106 

   107     /**

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

   109      */

   110     public final void eraseThreadLocals() {

   111         UNSAFE.putObject(this, THREAD_LOCALS, null);

   112         UNSAFE.putObject(this, INHERITABLE_THREAD_LOCALS, null);

   113     }

   114 

   115     // ensure run method is run only once

   116     private volatile boolean hasRun;

   117 

   118     @Override

   119     public void run() {

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

   121             hasRun = true;

   122             super.run();

   123         }

   124     }

   125 

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

   127     static {

   128         try {

   129             ACC = new AccessControlContext(new ProtectionDomain[] {

   130                 new ProtectionDomain(null, null)

   131             });

   132 

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

   134             UNSAFE = jdk.internal.misc.Unsafe.getUnsafe();

   135             Class<?> tk = Thread.class;

   136             Class<?> gk = ThreadGroup.class;

   137 

   138             THREAD_LOCALS = UNSAFE.objectFieldOffset(tk, "threadLocals");

   139             INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset

   140                     (tk, "inheritableThreadLocals");

   141             INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset

   142                 (tk, "inheritedAccessControlContext");

   143             CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset

   144                 (tk, "contextClassLoader");

   145 

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

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

   148             ThreadGroup group = (ThreadGroup)

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

   150 

   151             while (group != null) {

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

   153                 if (parent == null)

   154                     break;

   155                 group = parent;

   156             }

   157             final ThreadGroup root = group;

   158             INNOCUOUSTHREADGROUP = AccessController.doPrivileged(

   159                 new PrivilegedAction<ThreadGroup>() {

   160                     @Override

   161                     public ThreadGroup run() {

   162                         return new ThreadGroup(root, "InnocuousThreadGroup");

   163                     }

   164                 });

   165         } catch (Exception e) {

   166             throw new Error(e);

   167         }

   168     }

   169 }