Thread.sleep在ExecutorService循环中导致意外行为

Question

In below test class just "before" is outputted.

But if I removed Thread.sleep the following is outputted :

before
after
before
after
before
after
before
after
before
after
before
after
before
after
before
after
before
after
before
after

Which is what I expect.

When I use Thread.sleep I think that there should be a 1000ms delay between each output of

before
after

Why is this not occuring & how can the code be amended so that the generated output is same regardless of calling sleep or not ?

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import org.junit.Test;

public class RunExecutorTest {

    private ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

    private class RunTest implements Runnable {
        public void run() {

            System.out.println("before");

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            System.out.println("after");
        }
    }

    @Test
    public void testRun() {

        Runnable r = new RunTest();

        for(int counter = 0; counter < 10; ++counter) {  
            executor.execute(r);
        }
    }

}

Update from reading comment below "@user470184 It doesn't work in junit test cases because Junit kills all threads when the main thread completes. – Sotirios Delimanolis" if I add

try {
    Thread.sleep(10000);
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

at the end of test method then it works as expected.

Answer 1

When I use Thread.sleep I think that there should be a 1000ms delay between each output of

before after

Why is this not occuring & how can the code be amended so that the generated output is same regardless of calling sleep or not ?

The delay is clearly between before and after , not between each iteration of those

System.out.println("before");

try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}

System.out.println("after");

yielding

before
...1000 millis
after
before
...1000 millis
after

Perhaps I've misunderstood your question.

You do have a Thread pool of 1 thread.

private ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

All of this will be output sequentially.

---

As for why it's failing with JUnit, JUnit kills all threads when its main Thread completes execution. You cannot really control this (short of implementing your own wait mechanism).