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 139 (tk.getDeclaredField("threadLocals")); 140 INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset 141 (tk.getDeclaredField("inheritableThreadLocals")); 142 INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset 143 (tk.getDeclaredField("inheritedAccessControlContext")); 144 CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset 145 (tk.getDeclaredField("contextClassLoader")); 146 147 long tg = UNSAFE.objectFieldOffset(tk.getDeclaredField("group")); 148 long gp = UNSAFE.objectFieldOffset(gk.getDeclaredField("parent")); 149 ThreadGroup group = (ThreadGroup) 150 UNSAFE.getObject(Thread.currentThread(), tg); 151 152 while (group != null) { 153 ThreadGroup parent = (ThreadGroup)UNSAFE.getObject(group, gp); 154 if (parent == null) 155 break; 156 group = parent; 157 } 158 final ThreadGroup root = group; 159 INNOCUOUSTHREADGROUP = AccessController.doPrivileged( 160 new PrivilegedAction<ThreadGroup>() { 161 @Override 162 public ThreadGroup run() { 163 return new ThreadGroup(root, "InnocuousThreadGroup"); 164 } 165 }); 166 } catch (Exception e) { 167 throw new Error(e); 168 } 169 } 170 }