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 sun.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 

    49     public InnocuousThread(Runnable target) {

    50         this(INNOCUOUSTHREADGROUP, target,

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

    52     }

    53 

    54     public InnocuousThread(Runnable target, String name) {

    55         this(INNOCUOUSTHREADGROUP, target, name);

    56     }

    57 

    58     public InnocuousThread(ThreadGroup group, Runnable target, String name) {

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

    60         UNSAFE.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, ACC);

    61         UNSAFE.putOrderedObject(this, CONTEXTCLASSLOADER, ClassLoader.getSystemClassLoader());

    62     }

    63 

    64     @Override

    65     public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) {

    66         // silently fail

    67     }

    68 

    69     @Override

    70     public void setContextClassLoader(ClassLoader cl) {

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

    72         if (cl == null)

    73             super.setContextClassLoader(null);

    74         else

    75             throw new SecurityException("setContextClassLoader");

    76     }

    77 

    78     /**

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

    80      */

    81     public final void eraseThreadLocals() {

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

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

    84     }

    85 

    86     // ensure run method is run only once

    87     private volatile boolean hasRun;

    88 

    89     @Override

    90     public void run() {

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

    92             hasRun = true;

    93             super.run();

    94         }

    95     }

    96 

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

    98     static {

    99         try {

   100             ACC = new AccessControlContext(new ProtectionDomain[] {

   101                 new ProtectionDomain(null, null)

   102             });

   103 

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

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

   106             Class<?> tk = Thread.class;

   107             Class<?> gk = ThreadGroup.class;

   108 

   109             THREAD_LOCALS = UNSAFE.objectFieldOffset

   110                     (tk.getDeclaredField("threadLocals"));

   111             INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset

   112                     (tk.getDeclaredField("inheritableThreadLocals"));

   113             INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset

   114                 (tk.getDeclaredField("inheritedAccessControlContext"));

   115             CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset

   116                 (tk.getDeclaredField("contextClassLoader"));

   117 

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

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

   120             ThreadGroup group = (ThreadGroup)

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

   122 

   123             while (group != null) {

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

   125                 if (parent == null)

   126                     break;

   127                 group = parent;

   128             }

   129             final ThreadGroup root = group;

   130             INNOCUOUSTHREADGROUP = AccessController.doPrivileged(

   131                 (PrivilegedAction<ThreadGroup>) () ->

   132                     { return new ThreadGroup(root, "InnocuousThreadGroup"); });

   133         } catch (Exception e) {

   134             throw new Error(e);

   135         }

   136     }

   137 }