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