Java Future.get() 不返回

Question

从下面的代码或 ValueMutationEventHandler，为什么我不能执行 future2.get()，等待 future2 完成然后获取结果？

如果我执行 future2.get()，它将永远等待。

    import java.util.concurrent.BrokenBarrierException;
    import java.util.concurrent.CyclicBarrier;
    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.TimeoutException;

    import junit.framework.Assert;

    import org.junit.Test;

    import com.lmax.disruptor.BatchEventProcessor;
    import com.lmax.disruptor.ClaimStrategy;
    import com.lmax.disruptor.RingBuffer;
    import com.lmax.disruptor.WaitStrategy;

    int numPublisher = 1;
    int numConsumer = 1;
    int parties = numPublisher + numConsumer;
    CyclicBarrier barrier = new CyclicBarrier(parties);

    RingBuffer<ValueEvent> ringBuffer = new RingBuffer<ValueEvent>(
            ValueEvent.EVENT_FACTORY, 8192,
            ClaimStrategy.Option.MULTI_THREADED,
            WaitStrategy.Option.YIELDING
    );

    int iteration = 10;
    ValuePublisher valuePublisher = new ValuePublisher(
            barrier, ringBuffer, iteration
    );

    ExecutorService execService = Executors.newFixedThreadPool(2);
    Future future = execService.submit(valuePublisher);

    ValueMutationEventHandler eventHandler = new ValueMutationEventHandler(Operation.ADDITION);

    BatchEventProcessor<ValueEvent> eventProcessor = new BatchEventProcessor<ValueEvent>(ringBuffer, 
            ringBuffer.newDependencyBarrier(),
            eventHandler
    );

    barrier.await();
    Future future2 = execService.submit(eventProcessor);

    //////////////////////////////
    // Why do I need sleep here? Why doesn't future2.get works?
    /////////////////////////////
    Thread.sleep(1000);

    Assert.assertEquals(eventHandler.getValue(), 45L );

Answer 1

您可以使用 get(long timeout, TimeUnit unit) 以避免等待很长时间并使操作超时。

使用上面而不是 Thread.sleep(1000); ，你不需要 Thread.sleep(int)

如果 Future.get 没有返回某事，你可能需要检查BatchEventProcessor 查看那里发生了什么。如果它不返回任何内容，Future.get 也无法返回任何内容。将调试点放入 BatchEventProcessor 中，以确保它确实在您需要的预期时间范围内返回结果。