Question

在以下程序中，代码在方法get()中Future上尝试second()时会挂起！这是为什么？两个执行程序服务之间的唯一区别是它们使用的ThreadFactory。如果我使用newSingleThreadExecutor或newFixedThreadPool计数为1，则无关紧要。

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的runnable的线程：

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

而在你的第二家工厂，你只是忘了为创建的线程提供runnable：

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

所以，在你的第二种情况下，runnable永远不会运行，因此未来永远不会得到一个值。

将第二种情况下的线程创建更改为

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

Java ThreadFactory：为什么一个人使用作品而其他人不使用？

1 个答案: