对Java中interrupt、interrupted和isInterrupted的理解

对Java中interrupt、interrupted和isInterrupted的理解

一、示例

public class InterruptDemo {

    public static void main(String[] args) throws InterruptedException {

        Thread t = new Thread(() -> {

            System.out.println(Thread.currentThread().getName() + " start...");

            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                System.out.println(Thread.currentThread().getName() + " into catch");
                System.out.println("isInterrupted: " + Thread.currentThread().isInterrupted());
            }

            System.out.println(Thread.currentThread().getName() + " end...");

        });

        t.start();
        Thread.sleep(1000);

        t.interrupt();

        System.out.println("Main thread end...");

    }

}

输出：

Thread-0 start...
Main thread end...
Thread-0 into catch
isInterrupted: false
Thread-0 end...

本示例新建了一个线程，用主线程启动，主线程睡1s，再调用子线程的interrupt()方法，子线程由于也在睡着，被打断后，输出子线程中断状态。

这里子线程的isInterrupted()方法返回是false，讲道理的话，应该返回的是true才对，因为子线程确实被中断了。Thread.sleep源码注释：

     if any thread has interrupted the current thread. The <i>interrupted status</i> of the current thread is cleared when this exception is thrown.

意思是，如果任何一个线程打断了当前线程，当InterruptedException异常抛出时，那么当前线程的”中断状态“就被清除了。

 

二、Thread类的三个方法

2.1 interrupt

    public void interrupt() {
        if (this != Thread.currentThread())
            checkAccess();

        synchronized (blockerLock) {
            Interruptible b = blocker;
            if (b != null) {
                interrupt0();           // Just to set the interrupt flag
                b.interrupt(this);
                return;
            }
        }
        interrupt0();
    }

该方法的作用是中断线程，调用该方法的线程被设置为”中断状态“。需要特别注意，调用该方法的线程只是将线程设置为中断状态，至于线程是否真的中断，要取决于线程内部的逻辑。

2.2 isInterrupted

public class InterruptDemo {

    public static void main(String[] args) throws InterruptedException {

        Thread t = new Thread(() -> {

            System.out.println(Thread.currentThread().getName() + " start...");

            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                System.out.println(Thread.currentThread().getName() + " into catch");
                System.out.println("isInterrupted: " + Thread.currentThread().isInterrupted());
                Thread.currentThread().interrupt();
                System.out.println("after interrupt...isInterrupted: " + Thread.currentThread().isInterrupted());
            }

            System.out.println(Thread.currentThread().getName() + " end...");

        });

        t.start();
        Thread.sleep(1000);

        t.interrupt();

        System.out.println("Main thread end...");

    }

}

输出

Thread-0 start...
Main thread end...
Thread-0 into catch
isInterrupted: false
after interrupt...isInterrupted: true
Thread-0 end...

从输出结果来看，当再次调用interrupt()方法的时候，isInterrupted的值为true，说明isInterrupt()方法不改变中断状态，只显示当前的中断状态。

2.3 interrupted

public class InterruptDemo {

    public static void main(String[] args) throws InterruptedException {

        Thread t = new Thread(() -> {

            System.out.println(Thread.currentThread().getName() + " start...");

            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                System.out.println(Thread.currentThread().getName() + " into catch");
                System.out.println("isInterrupted: " + Thread.currentThread().isInterrupted());
                Thread.currentThread().interrupt();
                System.out.println("after interrupt...isInterrupted: " + Thread.currentThread().isInterrupted());
                Thread.interrupted();
                System.out.println("after interrupted...isInterrupted: " + Thread.currentThread().isInterrupted());
            }

            System.out.println(Thread.currentThread().getName() + " end...");

        });

        t.start();
        Thread.sleep(1000);

        t.interrupt();

        System.out.println("Main thread end...");

    }

}

输出

Thread-0 start...
Main thread end...
Thread-0 into catch
isInterrupted: false
after interrupt...isInterrupted: true
after interrupted...isInterrupted: false
Thread-0 end...

可以看到，interrupted只是重置了中断状态的静态方法。