在默认安全管理器下,如果我创建ExecutorService(在这种情况下为ThreadPoolExecutor),我无法将其关闭,shutdown()
只需调用checkPermission("modifyThread")
即可模具:
import java.util.concurrent.*;
class A {
public static void main( String[] args) {
Thread ct = Thread.currentThread();
System.out.println("current thread: " + ct);
ct.checkAccess(); // we have access to our own thread...
ThreadPoolExecutor tpe = new ThreadPoolExecutor(
1, // one core thread
1, // doesn't matter because queue is unbounded
0, TimeUnit.SECONDS, // doesn't matter in this case
new LinkedBlockingQueue<Runnable>(), /* unbound queue for
* our single thread */
new ThreadFactory() {
public Thread newThread(Runnable r) {
// obviously never gets called as we don't add any work
System.out.println("making thread");
return new Thread(r);
}
}
);
tpe.shutdown(); // raises security exception
}
}
Sun JDK:
$ java -Djava.security.manager A. 当前线程:线程[main,5,main] 线程“main”中的异常java.security.AccessControlException:访问被拒绝(java.lang.RuntimePermission modifyThread) 在 java.security.AccessControlContext.checkPermission(AccessControlContext.java:323) 在 java.security.AccessController.checkPermission(AccessController.java:546) 在 java.lang.SecurityManager.checkPermission(SecurityManager.java:532) 在 java.util.concurrent.ThreadPoolExecutor.shutdown(ThreadPoolExecutor.java:1094) 在A.main(A.java:22)
OpenJDK的:
$ java -Djava.security.manager A. 当前线程:线程[main,5,main] 线程“main”中的异常java.security.AccessControlException:访问被拒绝(java.lang.RuntimePermission modifyThread) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:342) at java.security.AccessController.checkPermission(AccessController.java:553) 在java.lang.SecurityManager.checkPermission(SecurityManager.java:549) at java.util.concurrent.ThreadPoolExecutor.checkShutdownAccess(ThreadPoolExecutor.java:711) at java.util.concurrent.ThreadPoolExecutor.shutdown(ThreadPoolExecutor.java:1351) 在A.main(A.java:22)
为什么??????? 什么是创建一个只有你控制并关闭它的线程池的安全隐患?这是实施中的错误,还是我错过了什么?
让我们看看ExecutorService.shutdown的规范是什么......
启动有序关闭,其中先前提交的任务已执行,但不会接受任何新任务。如果已经关闭,调用没有额外的效果。
抛出: SecurityException - 如果存在安全管理器并且关闭此ExecutorService可能会操纵不允许调用者修改的线程,因为它不包含RuntimePermission(“modifyThread”),或者安全管理器的checkAccess方法拒绝访问。
这......和它一样含糊不清。关于在ExecutorService的生命周期中制作的任何“系统线程”,规范说没有,而且它允许你提供自己的线程,这证明应该当你这样做时,请否“系统线程”。 (正如我在上面的示例源中所做的那样)
感觉就像Java SE实现者看到shutdown
可以引发SecurityException
,所以他们就像是,“哦,好吧,我只是在这里添加随机安全检查以确保合规性” ...
问题是,通过阅读OpenJDK源代码(openjdk-6-src-b20-21_jun_2010),结果发现仅方式任何线程都被创建,是通过调用你提供的ThreadFactory(由于我没有创建任何工作而从未在我的测试用例中调用过,我不会调用prestartCoreThread或preStartAllCoreThreads)。因此在OpenJDK的ThreadPoolExecutor中没有明显的原因进行安全检查(就像在sun-jdk-1.6中完成的那样,但是我没有源代码):
/**
* Initiates an orderly shutdown in which previously submitted
* tasks are executed, but no new tasks will be accepted.
* Invocation has no additional effect if already shut down.
*
* @throws SecurityException {@inheritDoc}
*/
public void shutdown() {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(SHUTDOWN);
interruptIdleWorkers();
onShutdown(); // hook for ScheduledThreadPoolExecutor
} finally {
mainLock.unlock();
}
tryTerminate();
}
在做任何事之前都会调用{p> checkShutdownAccess
...
/**
* If there is a security manager, makes sure caller has
* permission to shut down threads in general (see shutdownPerm).
* If this passes, additionally makes sure the caller is allowed
* to interrupt each worker thread. This might not be true even if
* first check passed, if the SecurityManager treats some threads
* specially.
*/
private void checkShutdownAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkPermission(shutdownPerm);
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
for (Worker w : workers)
security.checkAccess(w.thread);
} finally {
mainLock.unlock();
}
}
}
如您所见,无条件地在安全管理器上调用checkPermission(shutdownPerm)
.... shutdownPerm定义为......
private static final RuntimePermission shutdownPerm =
new RuntimePermission(“modifyThread”);
...据我所知,这完全没有意义,因为modifyThread
意味着访问系统线程,并且 没有系统线程在这里玩,事实上,根本没有线程,因为我没有提交任何工作或预启动,即使有线程,他们也是我的线程,因为我传入了{{ 1}}。该规范没有说明神奇的死亡,除了涉及系统线程(它们不是),可能有一个ThreadFactory
。
基本上,为什么我不能删除检查系统线程访问权限的行?我认为没有安全隐含要求它。怎么没有其他人遇到这个问题?我在问题跟踪器上看到了一个帖子,他们通过将对SecurityException
的调用更改为shutdownNow
来“解决”此问题,显然,这并没有为他们解决问题。
答案 0 :(得分:1)
这很简单:你不能在主线程组中做到这一点。它部分是为applet设计的。
从关机方法想法复制为什么?
如果这是一个问题,您可以自由使用PrivilegedAction来调用shutdown。请记住,Thread.interrupt()是无辜的,它也可能看起来throws SecurityException
。
要回答这个问题:只需确保您授予自己的代码权限,您就会感到高兴。或者“modifyThread”也可以自由授予,它主要由applet使用。
对于不受信任的代码:嗯,不受信任的代码甚至不应该处理其ThreadGroup之外的线程,因此提供API来创建ThreadPool,并允许关闭由调用者创建的。您可以根据呼叫者授予权限。
希望这有点帮助(问号的数量清楚地表明了绝望和最大的烦恼)
/*
* Conceptually, shutdown is just a matter of changing the
* runState to SHUTDOWN, and then interrupting any worker
* threads that might be blocked in getTask() to wake them up
* so they can exit. Then, if there happen not to be any
* threads or tasks, we can directly terminate pool via
* tryTerminate. Else, the last worker to leave the building
* turns off the lights (in workerDone).
*
* But this is made more delicate because we must cooperate
* with the security manager (if present), which may implement
* policies that make more sense for operations on Threads
* than they do for ThreadPools. This requires 3 steps:
*
* 1. Making sure caller has permission to shut down threads
* in general (see shutdownPerm).
*
* 2. If (1) passes, making sure the caller is allowed to
* modify each of our threads. This might not be true even if
* first check passed, if the SecurityManager treats some
* threads specially. If this check passes, then we can try
* to set runState.
*
* 3. If both (1) and (2) pass, dealing with inconsistent
* security managers that allow checkAccess but then throw a
* SecurityException when interrupt() is invoked. In this
* third case, because we have already set runState, we can
* only try to back out from the shutdown as cleanly as
* possible. Some workers may have been killed but we remain
* in non-shutdown state (which may entail tryTerminate from
* workerDone starting a new worker to maintain liveness.)
*/
答案 1 :(得分:0)
听起来像是懒惰和/或安全的实现。它不是检查是否涉及其他线程,而是假设有些线程。最好抛出一个安全例外而不是留下潜在的安全漏洞。