为什么ExecutorService不调用UncaughtExceptionHandler？

Question

我偶然发现了一个问题，可以总结如下：

当我手动创建线程（即通过实例化java.lang.Thread）时，UncaughtExceptionHandler将适当地调用它。但是，当我ExecutorService与一起使用时ThreadFactory，处理程序将被忽略。我错过了什么？

public class ThreadStudy {

private static final int THREAD_POOL_SIZE = 1;

public static void main(String[] args) {

    // create uncaught exception handler

    final UncaughtExceptionHandler exceptionHandler = new UncaughtExceptionHandler() {

        @Override
        public void uncaughtException(Thread t, Throwable e) {
            synchronized (this) {
                System.err.println("Uncaught exception in thread '" + t.getName() + "': " + e.getMessage());
            }
        }
    };

    // create thread factory

    ThreadFactory threadFactory = new ThreadFactory() {

        @Override
        public Thread newThread(Runnable r) {
            // System.out.println("creating pooled thread");
            final Thread thread = new Thread(r);
            thread.setUncaughtExceptionHandler(exceptionHandler);
            return thread;
        }
    };

    // create Threadpool

    ExecutorService threadPool = Executors.newFixedThreadPool(THREAD_POOL_SIZE, threadFactory);

    // create Runnable

    Runnable runnable = new Runnable() {

        @Override
        public void run() {
            // System.out.println("A runnable runs...");
            throw new RuntimeException("Error in Runnable");
        }
    };

    // create Callable

    Callable<Integer> callable = new Callable<Integer>() {

        @Override
        public Integer call() throws Exception {
            // System.out.println("A callable runs...");
            throw new Exception("Error in Callable");
        }
    };

    // a) submitting Runnable to threadpool
    threadPool.submit(runnable);

    // b) submit Callable to threadpool
    threadPool.submit(callable);

    // c) create a thread for runnable manually
    final Thread thread_r = new Thread(runnable, "manually-created-thread");
    thread_r.setUncaughtExceptionHandler(exceptionHandler);
    thread_r.start();

    threadPool.shutdown();
    System.out.println("Done.");
}
}

我期望：消息“未捕获的异常…”的三倍

我得到：消息一次（由手动创建的线程触发）。

在Windows 7和Mac OS X 10.5上用Java 1.6复制。

Answer 1

因为异常不会被捕获。

您的ThreadFactory生成的线程没有直接赋予您的Runnable或Callable。相反，您获得的Runnable是内部Worker类，例如，请参阅ThreadPoolExecutor
$ Worker。尝试System.out.println()在示例中为newThread提供Runnable。

该Worker捕获您提交的作业中的所有RuntimeException。

您可以在ThreadPoolExecutor＃afterExecute方法中获取异常。