Java ThreadFactory：为什么一个使用作品但其他不使用？

Question

In the following program the code hangs while trying to do get() on the Future in the method second() ! Why is that? The only difference between the two executor services are the ThreadFactory they use. It doesn't matter if I use newSingleThreadExecutor or newFixedThreadPool with count of 1.

package me.test;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;

public class ExecutorServiceTest {
    ThreadFactory tf1 = new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {
            Thread t = Executors.defaultThreadFactory().newThread(r);
            t.setDaemon(true);
            t.setName("tf1-thread");
            return t;
        }
    };
    ThreadFactory tf2 = new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread("tf2-thread");
            t.setDaemon(true);
            return t;
        }
    };
    ExecutorService service1 = Executors.newSingleThreadExecutor(tf1);
    ExecutorService service2 = Executors.newSingleThreadExecutor(tf2);
    Callable<Integer> callable = new Callable<Integer>() {
        @Override
        public Integer call() throws Exception {
            return 0;
        }
    };

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorServiceTest executorTest = new ExecutorServiceTest();
        executorTest.first(); // this returns
        executorTest.second(); // this hangs
        System.exit(0);
    }

    void first() throws ExecutionException, InterruptedException {
        Future<Integer> future = service1.submit(callable);
        int result = future.get();
        System.out.println("result=" + result);
    }
    void second() throws ExecutionException, InterruptedException {
        Future<Integer> future = service2.submit(callable);
        int result = future.get();
        System.out.println("result=" + result);
    }
}

Answer 1

Your first factory creates a thread that runs the specified runnable:

Thread t = Executors.defaultThreadFactory().newThread(r);

Whereas in your second factory you simply forgot to provide the runnable to the created thread:

Thread t = new Thread("tf2-thread");

So, in your second case, the runnable is never run, and so the future never gets a value.

Change the thread creation in the second case to

Thread t = new Thread(r, "tf2-thread");