java - ExecutorService FixThreadPool 作为共享参数不并行运行

Question

我正在尝试在 Java 8 中使用固定线程池，只要它保持在同一函数内，它就可以完美工作。一旦我尝试将执行器共享为参数，它就永远不会并行运行。

这很好用:

```

public static void test2() {

ExecutorService executor =  Executors.newFixedThreadPool(2);
try {
    CompletionService<Integer> myCompletionService = 
               new ExecutorCompletionService<Integer>(executor);


    myCompletionService.submit(()-> {
        try {
            TimeUnit.SECONDS.sleep(5);
            return 123;
        }
        catch (InterruptedException e) {
            throw new IllegalStateException("task interrupted", e);
        }
    });


    CompletionService<Integer> myCompletionService2 = 
               new ExecutorCompletionService<Integer>(executor);
    myCompletionService2.submit(()-> {
        try {
            TimeUnit.SECONDS.sleep(5);
            return 654;
        }
        catch (InterruptedException e) {
            throw new IllegalStateException("task interrupted", e);
        }
    });

    Future<Integer> myFuture = myCompletionService.take();
    Integer x = myFuture.get();
    System.out.println("Result = " + x);

    Future<Integer> myFuture2 = myCompletionService2.take();
    Integer y = myFuture2.get();
    System.out.println("Result = " + y);

    executor.shutdown();
} catch (InterruptedException | ExecutionException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}
}
```

但是一旦我将它们移动到三个函数中，例如:

```

static Integer t1(ExecutorService executor) throws InterruptedException, ExecutionException {
    CompletionService<Integer> myCompletionService = 
               new ExecutorCompletionService<Integer>(executor);


    myCompletionService.submit(()-> {
        try {
            TimeUnit.SECONDS.sleep(5);
            return 123;
        }
        catch (InterruptedException e) {
            throw new IllegalStateException("task interrupted", e);
        }
    });
    Future<Integer> myFuture = myCompletionService.take();
    return myFuture.get();
}

static Integer t2(ExecutorService executor) throws InterruptedException, ExecutionException {
    CompletionService<Integer> myCompletionService2 = 
               new ExecutorCompletionService<Integer>(executor);


    myCompletionService2.submit(()-> {
        try {
            TimeUnit.SECONDS.sleep(5);
            return 456;
        }
        catch (InterruptedException e) {
            throw new IllegalStateException("task interrupted", e);
        }
    });
    Future<Integer> myFuture2 = myCompletionService2.take();
    return myFuture2.get();
}

static void test3() {
    ExecutorService executor =  Executors.newFixedThreadPool(5);
    try {
        Integer x = t1(executor);
        Integer y = t2(executor);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ExecutionException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    executor.shutdown();
}

```现在 test3 将需要 10 秒，我预计它与顶部的测试相同，如果并行运行，则应该需要 5 秒。，

Answer 1

在提交后的 t1 中，您调用 get() 并被阻止，因此仅当第一个任务完成时(5 秒后)，您才从 t1 退出。

在第一个示例中，您提交了两个任务，以便它们开始在单独的线程中执行，然后仅调用 get() 来阻止并等待结果。