Java 线程工厂 : Why does one use of works but other doesn't?

Question

在以下程序中，代码在 second() 方法中尝试对 Future 执行 get() 时挂起!这是为什么？两个执行器服务之间的唯一区别是它们使用的 ThreadFactory。我使用 newSingleThreadExecutor 还是 newFixedThreadPool 计数为 1 都没有关系。

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

您的第一个工厂创建一个运行指定可运行对象的线程:

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

而在您的第二个工厂中，您只是忘记了向创建的线程提供可运行对象:

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

因此，在您的第二种情况下，runnable 永远不会运行，因此 future 永远不会获得值(value)。

将第二种情况的线程创建改成

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