java - 在 Java 中使用 Thread#stop() 来终止一个正在运行的线程是否可以接受？

Question

遗憾的是，在 Java 中对字符串使用正则表达式时无法指定超时。因此，如果您没有严格控制将哪些模式应用于哪些输入，您最终可能会拥有消耗大量 CPU 的线程，同时无休止地尝试将(设计不佳的)模式与(恶意的？)输入匹配。

我知道 Thread#stop() 被弃用的原因(参见 http://download.oracle.com/javase/1.5.0/docs/guide/misc/threadPrimitiveDeprecation.html )。它们以可能在 ThreadDeath 异常情况下损坏的对象为中心，然后这些对象会污染您正在运行的 JVM 环境并可能导致细微的错误。

对于比我对 JVM 的工作原理有更深入了解的任何人，我的问题是:如果需要停止的线程没有持有任何(明显的)监视器或对使用的对象的引用程序的其余部分，那么可以接受使用 Thread#stop() 吗？

我创建了一个相当防御性的解决方案，以便能够处理具有超时的正则表达式匹配。我很高兴收到任何评论或评论，尤其是关于这种方法可能导致的问题，尽管我努力避免这些问题。

谢谢!

import java.util.concurrent.Callable;

public class SafeRegularExpressionMatcher {

    // demonstrates behavior for regular expression running into catastrophic backtracking for given input
    public static void main(String[] args) {
        SafeRegularExpressionMatcher matcher = new SafeRegularExpressionMatcher(
                "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", "(x+x+)+y", 2000);
        System.out.println(matcher.matches());
    }

    final String stringToMatch;

    final String regularExpression;

    final int timeoutMillis;

    public SafeRegularExpressionMatcher(String stringToMatch, String regularExpression, int timeoutMillis) {
        this.stringToMatch = stringToMatch;
        this.regularExpression = regularExpression;
        this.timeoutMillis = timeoutMillis;
    }

    public Boolean matches() {
        CallableThread<Boolean> thread = createSafeRegularExpressionMatchingThread();
        Boolean result = tryToGetResultFromThreadWithTimeout(thread);
        return result;
    }

    private CallableThread<Boolean> createSafeRegularExpressionMatchingThread() {
        final String stringToMatchForUseInThread = new String(stringToMatch);
        final String regularExpressionForUseInThread = new String(regularExpression);
        Callable<Boolean> callable = createRegularExpressionMatchingCallable(stringToMatchForUseInThread,
                regularExpressionForUseInThread);
        CallableThread<Boolean> thread = new CallableThread<Boolean>(callable);
        return thread;
    }

    private Callable<Boolean> createRegularExpressionMatchingCallable(final String stringToMatchForUseInThread,
            final String regularExpressionForUseInThread) {
        Callable<Boolean> callable = new Callable<Boolean>() {
            public Boolean call() throws Exception {
                return Boolean.valueOf(stringToMatchForUseInThread.matches(regularExpressionForUseInThread));
            }
        };
        return callable;
    }

    private Boolean tryToGetResultFromThreadWithTimeout(CallableThread<Boolean> thread) {
        startThreadAndApplyTimeout(thread);
        Boolean result = processThreadResult(thread);
        return result;
    }

    private void startThreadAndApplyTimeout(CallableThread<Boolean> thread) {
        thread.start();
        try {
            thread.join(timeoutMillis);
        } catch (InterruptedException e) {
            throwRuntimeException("Interrupt", e);
        }
    }

    private Boolean processThreadResult(CallableThread<Boolean> thread) {
        Boolean result = null;
        if (thread.isAlive()) {
            killThread(thread); // do not use anything from the thread anymore, objects may be damaged!
            throwRuntimeException("Timeout", null);
        } else {
            Exception exceptionOccurredInThread = thread.getException();
            if (exceptionOccurredInThread != null) {
                throwRuntimeException("Exception", exceptionOccurredInThread);
            } else {
                result = thread.getResult();
            }
        }
        return result;
    }

    private void throwRuntimeException(String situation, Exception e) {
        throw new RuntimeException(situation + " occured while applying pattern /" + regularExpression + "/ to input '"
                + stringToMatch + " after " + timeoutMillis + "ms!", e);
    }

    /**
     * This method uses {@link Thread#stop()} to kill a thread that is running wild. Although it is acknowledged that
     * {@link Thread#stop()} is inherently unsafe, the assumption is that the thread to kill does not hold any monitors on or
     * even references to objects referenced by the rest of the JVM, so it is acceptable to do this.
     * 
     * After calling this method nothing from the thread should be used anymore!
     * 
     * @param thread Thread to stop
     */
    @SuppressWarnings("deprecation")
    private static void killThread(CallableThread<Boolean> thread) {
        thread.stop();
    }

    private static class CallableThread<V> extends Thread {

        private final Callable<V> callable;

        private V result = null;

        private Exception exception = null;

        public CallableThread(Callable<V> callable) {
            this.callable = callable;
        }

        @Override
        public void run() {
            try {
                V result = compute();
                setResult(result);
            } catch (Exception e) {
                exception = e;
            } catch (ThreadDeath e) {
                cleanup();
            }
        }

        private V compute() throws Exception {
            return callable.call();
        }

        private synchronized void cleanup() {
            result = null;
        }

        private synchronized void setResult(V result) {
            this.result = result;
        }

        public synchronized V getResult() {
            return result;
        }

        public synchronized Exception getException() {
            return exception;
        }

    }

}

编辑:

感谢 dawce 将我指向 this solution我已经能够在不需要额外线程的情况下解决我原来的问题。我已经在那里发布了代码。感谢所有回复的人。

Answer 1

如果您确定 Thread.stop() 是您唯一可用的解决方案，则可以使用它。您可能需要关闭并重新启动您的应用程序以确保其处于良好状态。

注意:线程可以捕获并忽略 ThreadDeath，因此不能保证停止所有线程。

另一种停止线程的方法是在不同的进程中运行它。这可以根据需要被杀死。这仍然会使资源处于不一致的状态(如锁定文件)，但这种情况不太可能也更容易控制。

当然，最好的解决方案是修复代码，使其一开始就不会这样做，而是尊重 Thread.interrupt()。