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 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 new PrivilegedAction<ThreadGroup>() { 132 @Override 133 public ThreadGroup run() { 134 return new ThreadGroup(root, "InnocuousThreadGroup"); 135 } 136 }); 137 } catch (Exception e) { 138 throw new Error(e); 139 } 140 } 141 }