Question

我是线程的新手。我怎样才能使t.join工作，调用它的线程等到t执行完毕？

这段代码只会冻结程序，因为线程正在等待自己死掉，对吗？

public static void main(String[] args) throws InterruptedException {
    Thread t0 = new Thready();
    t0.start();

}

@Override
public void run() {
    for (String s : info) {
        try {
            join();
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.printf("%s %s%n", getName(), s);
    }   
}

如果我想要有两个线程，我会怎么做，其中一个线程打印出info数组的一半，然后等待另一个完成，然后再做其余的？

Answer 1

使用类似的东西：

public void executeMultiThread(int numThreads)
   throws Exception
{
    List threads = new ArrayList();

    for (int i = 0; i < numThreads; i++)
    {
        Thread t = new Thread(new Runnable()
        {
            public void run()
            {
                // do your work
            }
        });

        // System.out.println("STARTING: " + t);
        t.start();
        threads.add(t);
    }

    for (int i = 0; i < threads.size(); i++)
    {
        // Big number to wait so this can be debugged
        // System.out.println("JOINING: " + threads.get(i));
        ((Thread)threads.get(i)).join(1000000);
    }

Answer 2

如果otherThread是另一个线程，你可以这样做：

@Override
public void run() {
    int i = 0;
    int half = (info.size() / 2);

    for (String s : info) {
        i++;
        if (i == half) {
        try {
            otherThread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.printf("%s %s%n", getName(), s);
        Thread.yield(); //Give other threads a chance to do their work
    }       
}

Sun的Java教程： http://java.sun.com/docs/books/tutorial/essential/concurrency/join.html

Answer 3

你必须在另一个线程上调用join方法类似的东西：

@Override
public void run() {
    String[] info = new String[] {"abc", "def", "ghi", "jkl"};

    Thread other = new OtherThread();
    other.start();

    for (int i = 0; i < info.length; i++) {
        try {
            if (i == info.length / 2) {
                other.join();    // wait for other to terminate
            }
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.printf("%s %s%n", getName(), info[i]);
    }       
}

Java：如何使用Thread.join

3 个答案: