java - 如何调整3个线程的控制流？

// Task 1 -- the main thread
        SimilarityResponse w2vResponse = questionClassifier.compute(questionInfo);

        // Task 2
        String sku = questionInfo.getSku();
        String question = questionInfo.getQuestion();
        Callable<ResponseList> dssmTask = () -> this.dssmCompute(sku, question);
        Future<ResponseList> dssmService = executorService.submit(dssmTask);
        ResponseList dssmResponse;
        try {
            LOGGER.info("start dssm ... {} ", question);
            dssmResponse = dssmService.get(Parameters.getParserTimeLimit(), TimeUnit.MILLISECONDS);
            LOGGER.info("dssmResponse ... {} ", dssmResponse);
        } catch (ExecutionException | InterruptedException e) {
            LOGGER.warn("ExecutionException | InterruptedException");
            e.printStackTrace();
        } catch (TimeoutException te) {
            dssmService.cancel(true);
            LOGGER.warn("DSSM time out for {} {}", sku, question);
        }

        // Task 3
        Callable<ResponseList> stsTask = () -> this.stsCompute(sku, question);
        Future<ResponseList> stsService = executorService.submit(stsTask);
        ResponseList stsResponse;
        try {
            LOGGER.info("start sts ... {} ", question);
            stsResponse = stsService.get(Parameters.getParserTimeLimit(), TimeUnit.MILLISECONDS);
            LOGGER.info("stsResponse ... {} ", stsResponse);
        } catch (ExecutionException | InterruptedException e) {
            LOGGER.warn("ExecutionException | InterruptedException");
            e.printStackTrace();
        } catch (TimeoutException te) {
            stsService.cancel(true);
            LOGGER.warn("STS time out for {} {}", sku, question);
        }

        // Last step == do something for above
        SimilarityResponse ensemble = new SimilarityResponse();
        return ensemble;

在执行最后一步之前，如何确定任务1-3已经完成？当前代码似乎先完成任务1，然后直接返回。

最佳答案

您应该使用CountDownLatch。在您的主线程中创建它的实例，然后将此实例传递给您的任务（可调用对象）。然后，当任务完成时，调用latch.countDown（）。在代码的最后一步中，调用latch.await（）以等待每个任务完成。看起来像这样（如果您的可调用对象是作为lambda创建的）：

final CountDownLatch latch = new CountDownLatch(3);

for(int x = 0; x < 3; x++) {
    service.submit( () -> {
        // do something
        latch.countDown();
    });
}

// in the end wait for tasks to finish
latch.await();