java - 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，会适本地调用 UncaughtExceptionHandler。但是，当我将 ExecutorService 与 ThreadFactory 一起使用时，将省略处理程序。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 上使用 Java 1.6 复制。

Answer 1

因为异常不会被捕获。

您的 ThreadFactory 生成的 Thread 没有直接给您 Runnable 或 Callable。相反，您获得的 Runnable 是一个内部 Worker 类，例如参见 ThreadPoolExecutor$Worker。在示例中为 newThread 提供的 Runnable 上尝试 System.out.println()。

此 Worker 从您提交的作业中捕获任何 RuntimeExceptions。

您可以在 ThreadPoolExecutor#afterExecute 中获得异常。方法。