在单元测试中运行多个线程

Question

Below is a unit test which uses ScheduledExecutorService to execute a scheduled runnable every second :

   import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import org.junit.Test;

public class ConcurrentRequestSimulator {

    private static final int NUMBER_REQUESTS = 4;

    @Test
    public void testGetToDoList() {

        try {
            ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(10);
            scheduler.scheduleAtFixedRate(new RequestThreadInvoker(), 0, 1, TimeUnit.SECONDS);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private final class RequestThreadInvoker implements Runnable {

        public void run() {

            ExecutorService es = Executors.newCachedThreadPool();
            for (int i = 1; i <= NUMBER_REQUESTS; i++) {
                es.execute(new RequestThread());
            }
            es.shutdown();

            while (!es.isTerminated()) {

            }

        }
    }

    private final class RequestThread implements Runnable {

        public void run() {
            try {
                System.out.println("in RequestThread");
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

}

The line System.out.println("in RequestThread"); in RequestThread does not appear to be invoked as no output is displayed to console. I think the issue is that since the test runs to completion, it causes the scheduler to stop scheduling? Can the test be updated so that scheduler is not terminated and RequestThreadInvoker is invoked repeatedly once per second ?

In RequestThreadInvoker I create a new instance of ExecutorService . Could this be causing the issue ?

Answer 1

Adding Thread.sleep(99000); to end of test causes test to wait 99 seconds which is enough time for test to run.

Answer 2

You'll need to block the main test thread (sleep/wait) while the thread pools are running. To perform assertions from one of the separate threads you can use something like concurrentunit .