java 线程池 异常 处理 机制 分析

public class ThreadTest {

    public static void main(String[] args) {
        ExecutorService exe = Executors.newFixedThreadPool(10);
        ExecutorCompletionService com  =  new ExecutorCompletionService(exe);
        Future future = com.submit(new Runnable(){
            @Override
            public void run() {
				throw new RuntimeException();
            }},"success");

        try{
            System.out.println(com.take().get());
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

上述代码只有在调用get()时抛出异常，否则不打印任何异常信息，查看源码得到原因如下：

public Future<V> submit(Runnable task, V result) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<V> f = newTaskFor(task, result);
        executor.execute(new QueueingFuture(f));
        return f;
    }

ExecutorCompletionService 的submit方法将Runnable 包装为一个RunnableFuture，而RunnableFuture的实现类为FutureTask，FutureTask的run方法如下：

public void run() {
        sync.innerRun();
    }

void innerRun() {
            if (!compareAndSetState(READY, RUNNING))
                return;

            runner = Thread.currentThread();
            if (getState() == RUNNING) { // recheck after setting thread
                V result;
                try {
                    result = callable.call();
                } catch (Throwable ex) {
                    setException(ex);
                    return;
                }
                set(result);
            } else {
                releaseShared(0); // cancel
            }
        }

可以看出当程序抛出异常时，没有打印任何异常信息，只是调用setException(ex)，将异常信息赋值给 exception变量。当调用future.get()方法时，抛出异常，代码如下：

V innerGet() throws InterruptedException, ExecutionException {
            acquireSharedInterruptibly(0);
            if (getState() == CANCELLED)
                throw new CancellationException();
            if (exception != null)
                throw new ExecutionException(exception);
            return result;
        }