单个 Thread.interrupt() 中断不止一次

Question

我创建了 MyTask，它在 run() 中有 3 件事要做。我尝试 interrupt() 持有 MyTask 实例的线程。不幸的是，一旦它被打断，它就会结束，并且只有字符串 First task 会打印在控制台上。

public class MyTask implements Runnable {
    private volatile Thread thread;

    @Override
    public void run() {
        while (!thread.isInterrupted()) {
            System.out.println("First task");
        }
        while (!thread.isInterrupted()) {
            System.out.println("Second task");
        }
        while (!thread.isInterrupted()) {
            System.out.println("Third task");
        }
    }

    public Thread start(){
        thread = new Thread(this);
        thread.start();
        return thread;
    }


    public static void main(String[] args) throws InterruptedException {
        Thread t = new MyTask().start();
        Thread.sleep(1000);
        t.interrupt();
        Thread.sleep(1000);
        t.interrupt();
        Thread.sleep(1000);
        t.interrupt();
    }

}

如果我在 run() 中添加 Thread.sleep(10) 它开始 正常工作 并打印 First task、Second task 和终于在控制台上 Third task。

问题是：为什么 Thread.interrupts() 只有添加 sleep() 才能正常工作？

public class MyTask implements Runnable {
    private volatile Thread thread;

    @Override
    public void run() {
        while (!thread.isInterrupted()) {
            System.out.println("First task");
        }
        try {
            Thread.sleep(10);
        } catch (Exception e) {
        }
        while (!thread.isInterrupted()) {
            System.out.println("Second task");
        }
        try {
            Thread.sleep(10);
        } catch (Exception e) {
        }
        while (!thread.isInterrupted()) {
            System.out.println("Third task");
        }
    }

    public Thread start(){
        thread = new Thread(this);
        thread.start();
        return thread;
    }


    public static void main(String[] args) throws InterruptedException {
        Thread t = new MyTask().start();
        Thread.sleep(1000);
        t.interrupt();
        Thread.sleep(1000);
        t.interrupt();
        Thread.sleep(1000);
        t.interrupt();
    }

}

Answer 1

查看 Thread.sleep(long)

上的 Javadoc

Throws: InterruptedException - if any thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.

因此，添加 sleep 以及捕获（和忽略）任何异常都会导致观察到的行为。

示例：

没有 sleep():

线程以 interrupted = false 开始，因此第一个循环运行s
线程被中断，即现在 interrupted = true
第一个循环检查 interrupted 但不检查运行（再次）
第二个循环检查 interrupted 而根本不检查运行
第 3 次循环检查 interrupted 而根本不检查运行
完成

随着sleep()

线程开始于 interrupted = false
循环 1:
- 检查条件并执行正文，因为 interrupted = false
- 线程被中断，即现在 interrupted = true
- while 条件被检查但是这次 interrupted = true 所以循环结束
- sleep() 被调用，由于线程已被中断，因此抛出异常并再次 interrupted = false
- 异常被捕获（并被忽略），因此继续正常执行
循环 2 和循环 3 重复步骤 2
完成

Answer 2

引用自Interrupts：

When a thread checks for an interrupt by invoking the static method Thread.interrupted, interrupt status is cleared. The non-static isInterrupted method, which is used by one thread to query the interrupt status of another, does not change the interrupt status flag.

含义：将您的代码从 thread.isInterrupted() 更改为 Thread.interrupted()，然后重试。

循环之间的 sleep() 也会通过立即抛出 InterruptedException 来清除该标志（因为当前线程已被中断）

单个 Thread.interrupt() 中断不止一次

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