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InnocuousThread.java
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InnocuousThread.java
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/*
* Copyright (c) 2013, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package jdk.internal.misc;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.ProtectionDomain;
import java.security.PrivilegedAction;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A thread that has no permissions, is not a member of any user-defined
* ThreadGroup and supports the ability to erase ThreadLocals.
*/
public final class InnocuousThread extends Thread {
private static final jdk.internal.misc.Unsafe UNSAFE;
private static final long THREAD_LOCALS;
private static final long INHERITABLE_THREAD_LOCALS;
private static final ThreadGroup INNOCUOUSTHREADGROUP;
private static final AccessControlContext ACC;
private static final long INHERITEDACCESSCONTROLCONTEXT;
private static final long CONTEXTCLASSLOADER;
private static final AtomicInteger threadNumber = new AtomicInteger(1);
private static String newName() {
return "InnocuousThread-" + threadNumber.getAndIncrement();
}
/**
* Returns a new InnocuousThread with an auto-generated thread name,
* and its context class loader is set to the system class loader.
*/
public static Thread newThread(Runnable target) {
return newThread(newName(), target);
}
/**
* Returns a new InnocuousThread with its context class loader
* set to the system class loader.
*/
public static Thread newThread(String name, Runnable target) {
return newThread(name, target, -1);
}
/**
* Returns a new InnocuousThread with its context class loader
* set to the system class loader. The thread priority will be
* set to the given priority.
*/
public static Thread newThread(String name, Runnable target, int priority) {
if (System.getSecurityManager() == null) {
return createThread(name, target, ClassLoader.getSystemClassLoader(), priority);
}
return AccessController.doPrivileged(
new PrivilegedAction<Thread>() {
@Override
public Thread run() {
return createThread(name, target, ClassLoader.getSystemClassLoader(), priority);
}
});
}
/**
* Returns a new InnocuousThread with an auto-generated thread name.
* Its context class loader is set to null.
*/
public static Thread newSystemThread(Runnable target) {
return newSystemThread(newName(), target);
}
/**
* Returns a new InnocuousThread with null context class loader.
*/
public static Thread newSystemThread(String name, Runnable target) {
return newSystemThread(name, target, -1);
}
/**
* Returns a new InnocuousThread with null context class loader.
* Thread priority is set to the given priority.
*/
public static Thread newSystemThread(String name, Runnable target, int priority) {
if (System.getSecurityManager() == null) {
return createThread(name, target, null, priority);
}
return AccessController.doPrivileged(
new PrivilegedAction<Thread>() {
@Override
public Thread run() {
return createThread(name, target, null, priority);
}
});
}
private static Thread createThread(String name, Runnable target, ClassLoader loader, int priority) {
Thread t = new InnocuousThread(INNOCUOUSTHREADGROUP,
target, name, loader);
if (priority >= 0) {
t.setPriority(priority);
}
return t;
}
private InnocuousThread(ThreadGroup group, Runnable target, String name, ClassLoader tccl) {
super(group, target, name, 0L, false);
UNSAFE.putObjectRelease(this, INHERITEDACCESSCONTROLCONTEXT, ACC);
UNSAFE.putObjectRelease(this, CONTEXTCLASSLOADER, tccl);
}
@Override
public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) {
// silently fail
}
@Override
public void setContextClassLoader(ClassLoader cl) {
// Allow clearing of the TCCL to remove the reference to the system classloader.
if (cl == null)
super.setContextClassLoader(null);
else
throw new SecurityException("setContextClassLoader");
}
/**
* Drops all thread locals (and inherited thread locals).
*/
public final void eraseThreadLocals() {
UNSAFE.putObject(this, THREAD_LOCALS, null);
UNSAFE.putObject(this, INHERITABLE_THREAD_LOCALS, null);
}
// ensure run method is run only once
private volatile boolean hasRun;
@Override
public void run() {
if (Thread.currentThread() == this && !hasRun) {
hasRun = true;
super.run();
}
}
// Use Unsafe to access Thread group and ThreadGroup parent fields
static {
try {
ACC = new AccessControlContext(new ProtectionDomain[] {
new ProtectionDomain(null, null)
});
// Find and use topmost ThreadGroup as parent of new group
UNSAFE = jdk.internal.misc.Unsafe.getUnsafe();
Class<?> tk = Thread.class;
Class<?> gk = ThreadGroup.class;
THREAD_LOCALS = UNSAFE.objectFieldOffset(tk, "threadLocals");
INHERITABLE_THREAD_LOCALS = UNSAFE.objectFieldOffset
(tk, "inheritableThreadLocals");
INHERITEDACCESSCONTROLCONTEXT = UNSAFE.objectFieldOffset
(tk, "inheritedAccessControlContext");
CONTEXTCLASSLOADER = UNSAFE.objectFieldOffset
(tk, "contextClassLoader");
long tg = UNSAFE.objectFieldOffset(tk, "group");
long gp = UNSAFE.objectFieldOffset(gk, "parent");
ThreadGroup group = (ThreadGroup)
UNSAFE.getObject(Thread.currentThread(), tg);
while (group != null) {
ThreadGroup parent = (ThreadGroup)UNSAFE.getObject(group, gp);
if (parent == null)
break;
group = parent;
}
final ThreadGroup root = group;
if (System.getSecurityManager() == null) {
INNOCUOUSTHREADGROUP = new ThreadGroup(root, "InnocuousThreadGroup");
} else {
INNOCUOUSTHREADGROUP = AccessController.doPrivileged(
new PrivilegedAction<ThreadGroup>() {
@Override
public ThreadGroup run() {
return new ThreadGroup(root, "InnocuousThreadGroup");
}
});
}
} catch (Exception e) {
throw new Error(e);
}
}
}