1 /*
   2  * Copyright (c) 2015, 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 package com.sun.org.apache.xml.internal.utils;
  26 
  27 import sun.misc.Unsafe;
  28 
  29 /**
  30  * This is a combination of ThreadControllerWrapper's inner class SafeThread
  31  * that was introduced as a fix for CR 6607339
  32  * and sun.misc.ManagedLocalsThread, a thread that has it's thread locals, and
  33  * inheritable thread locals erased on construction. Except the run method,
  34  * it is identical to sun.misc.ManagedLocalsThread.
  35  */
  36 public class SafeThread extends Thread {
  37 
  38     private static final Unsafe UNSAFE;
  39     private static final long THREAD_LOCALS;
  40     private static final long INHERITABLE_THREAD_LOCALS;
  41 
  42     private volatile boolean ran = false;
  43 
  44     public SafeThread(Runnable target) {
  45         super(target);
  46         eraseThreadLocals();
  47     }
  48 
  49     public SafeThread(Runnable target, String name) {
  50         super(target, name);
  51         eraseThreadLocals();
  52     }
  53 
  54     public SafeThread(ThreadGroup group, Runnable target, String name) {
  55         super(group, target, name);
  56         eraseThreadLocals();
  57     }
  58 
  59     public final void run() {
  60         if (Thread.currentThread() != this) {
  61             throw new IllegalStateException("The run() method in a"
  62                     + " SafeThread cannot be called from another thread.");
  63         }
  64         synchronized (this) {
  65             if (!ran) {
  66                 ran = true;
  67             } else {
  68                 throw new IllegalStateException("The run() method in a"
  69                         + " SafeThread cannot be called more than once.");
  70             }
  71         }
  72         super.run();
  73     }
  74 
  75     /**
  76      * Drops all thread locals (and inherited thread locals).
  77      */
  78     public final void eraseThreadLocals() {
  79         UNSAFE.putObject(this, THREAD_LOCALS, null);
  80         UNSAFE.putObject(this, INHERITABLE_THREAD_LOCALS, null);
  81     }
  82 
  83     static {
  84         UNSAFE = Unsafe.getUnsafe();
  85         Class<?> t = Thread.class;
  86         try {
  87             THREAD_LOCALS = UNSAFE.objectFieldOffset(t.getDeclaredField("threadLocals"));
  88             INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset(t.getDeclaredField("inheritableThreadLocals"));
  89         } catch (Exception e) {
  90             throw new Error(e);
  91         }
  92     }
  93 
  94 }