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 * @implNote Based on the implementation of InnocuousForkJoinWorkerThread. 39 */ 40 public final class InnocuousThread extends Thread { 41 private static final Unsafe UNSAFE; 42 private static final long THREAD_LOCALS; 43 private static final long INHERITABLE_THREAD_LOCALS; 44 private static final ThreadGroup INNOCUOUSTHREADGROUP; 45 private static final AccessControlContext ACC; 46 private static final long INHERITEDACCESSCONTROLCONTEXT; 47 private static final long CONTEXTCLASSLOADER; 48 49 private static final AtomicInteger threadNumber = new AtomicInteger(1); 50 private static String newName() { 51 return "InnocuousThread-" + threadNumber.getAndIncrement(); 52 } 53 54 /** 55 * Returns a new InnocuousThread with an auto-generated thread name. 56 * Its context class loader is set to null. 57 */ 58 public static Thread newSystemThread(Runnable target) { 59 return newSystemThread(newName(), target); 60 } 61 62 /** 63 * Returns a new InnocuousThread with null context class loader. 64 */ 65 public static Thread newSystemThread(String name, Runnable target) { 66 return new InnocuousThread(INNOCUOUSTHREADGROUP, 67 target, name, null); 68 } 69 70 public InnocuousThread(Runnable target) { 71 super(INNOCUOUSTHREADGROUP, target, newName()); 72 UNSAFE.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, ACC); 73 eraseThreadLocals(); 74 } 75 76 private InnocuousThread(ThreadGroup group, Runnable target, String name, ClassLoader tccl) { 77 super(group, target, name, 0L); 78 UNSAFE.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, ACC); 79 UNSAFE.putOrderedObject(this, CONTEXTCLASSLOADER, tccl); 80 eraseThreadLocals(); 81 } 82 83 @Override 84 public ClassLoader getContextClassLoader() { 85 // always report system class loader 86 return ClassLoader.getSystemClassLoader(); 87 } 88 89 @Override 90 public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { 91 // silently fail 92 } 93 94 @Override 95 public void setContextClassLoader(ClassLoader cl) { 96 throw new SecurityException("setContextClassLoader"); 97 } 98 99 // ensure run method is run only once 100 private volatile boolean hasRun; 101 102 @Override 103 public void run() { 104 if (Thread.currentThread() == this && !hasRun) { 105 hasRun = true; 106 super.run(); 107 } 108 } 109 110 /** 111 * Drops all thread locals (and inherited thread locals). 112 */ 113 public void eraseThreadLocals() { 114 UNSAFE.putObject(this, THREAD_LOCALS, null); 115 UNSAFE.putObject(this, INHERITABLE_THREAD_LOCALS, null); 116 } 117 118 // Use Unsafe to access Thread group and ThreadGroup parent fields 119 static { 120 try { 121 ACC = new AccessControlContext(new ProtectionDomain[] { 122 new ProtectionDomain(null, null) 123 }); 124 125 // Find and use topmost ThreadGroup as parent of new group 126 UNSAFE = Unsafe.getUnsafe(); 127 Class<?> tk = Thread.class; 128 Class<?> gk = ThreadGroup.class; 129 130 THREAD_LOCALS = UNSAFE.objectFieldOffset 131 (tk.getDeclaredField("threadLocals")); 132 INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset 133 (tk.getDeclaredField("inheritableThreadLocals")); 134 INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset 135 (tk.getDeclaredField("inheritedAccessControlContext")); 136 CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset 137 (tk.getDeclaredField("contextClassLoader")); 138 139 long tg = UNSAFE.objectFieldOffset(tk.getDeclaredField("group")); 140 long gp = UNSAFE.objectFieldOffset(gk.getDeclaredField("parent")); 141 ThreadGroup group = (ThreadGroup) 142 UNSAFE.getObject(Thread.currentThread(), tg); 143 144 while (group != null) { 145 ThreadGroup parent = (ThreadGroup)UNSAFE.getObject(group, gp); 146 if (parent == null) 147 break; 148 group = parent; 149 } 150 final ThreadGroup root = group; 151 INNOCUOUSTHREADGROUP = AccessController.doPrivileged( 152 new PrivilegedAction<ThreadGroup>() { 153 @Override 154 public ThreadGroup run() { 155 return new ThreadGroup(root, "InnocuousThreadGroup"); 156 } 157 }); 158 } catch (Exception e) { 159 throw new Error(e); 160 } 161 } 162 }