用interrupt()中斷Java線程

from  http://hapinwater.iteye.com/blog/310558

最近在學習Java線程相關的東西，和大家分享一下，有錯誤之處歡迎大家指正．

假如我們有一個任務如下，交給一個Java線程來執行，如何才能保證調用interrupt()來中斷它呢？

class ATask implements Runnable{

    private double d = 0.0;

    public void run() {
        //死循環執行打印"I am running!" 和做消耗時間的浮點計算
        while (true) {
            System.out.println("I am running!");

            for (int i = 0; i < 900000; i++) {
                d =  d + (Math.PI + Math.E) / d;
            }
            //給線程調度器可以切換到其它進程的信號
            Thread.yield();
        }
    }
}

public class InterruptTaskTest {

    public static void main(String[] args) throws Exception{
        //將任務交給一個線程執行
        Thread t = new Thread(new ATask());
        t.start();

        //運行一斷時間中斷線程
        Thread.sleep(100);
        System.out.println("****************************");
        System.out.println("Interrupted Thread!");
        System.out.println("****************************");
        t.interrupt();
    }
}

運行這個程序，我們發現調用interrupt()後，程序仍在運行，如果不強制結束，程序將一直運行下去，如下所示:

......
I am running!
I am running!
I am running!
I am running!
****************************
Interrupted Thread!
****************************
I am running!
I am running!
I am running!
I am running!
I am running!
....

雖然中斷髮生了，但線程仍然在進行，離開線程有兩種常用的方法：
拋出InterruptedException和用Thread.interrupted()檢查是否發生中斷,下面分別看一下這兩種方法：
1.在阻塞操作時如Thread.sleep()時被中斷會拋出InterruptedException(注意，進行不能中斷的IO操作而阻塞和要獲得對象的鎖調用對象的synchronized方法而阻塞時不會拋出InterruptedException)

class ATask implements Runnable{

    private double d = 0.0;

    public void run() {
        //死循環執行打印"I am running!" 和做消耗時間的浮點計算
        try {
            while (true) {
                System.out.println("I am running!");

                for (int i = 0; i < 900000; i++) {
                    d =  d + (Math.PI + Math.E) / d;
                }
                //休眠一斷時間,中斷時會拋出InterruptedException
                Thread.sleep(50);
            }
        } catch (InterruptedException e) {
            System.out.println("ATask.run() interrupted!");
        }
    }
}

程序運行結果如下:

I am running!
I am running!
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!

可以看到中斷任務時讓任務拋出InterruptedException來離開任務．

2.Thread.interrupted()檢查是否發生中斷.Thread.interrupted()能告訴你線程是否發生中斷,並將清除中斷狀態標記，所以程序不會兩次通知你線程發生了中斷．

class ATask implements Runnable{

    private double d = 0.0;

    public void run() {

        //檢查程序是否發生中斷
        while (!Thread.interrupted()) {
            System.out.println("I am running!");

            for (int i = 0; i < 900000; i++) {
                d = d + (Math.PI + Math.E) / d;
            }
        }

        System.out.println("ATask.run() interrupted!");
    }
}

程序運行結果如下：

I am running!
I am running!
I am running!
I am running!
I am running!
I am running!
I am running!
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!

我們可結合使用兩種方法來達到可以通過interrupt()中斷線程.請看下面例子:

class ATask implements Runnable{

    private double d = 0.0;

    public void run() {

        try {
        //檢查程序是否發生中斷
        while (!Thread.interrupted()) {
            System.out.println("I am running!");
            //point1 before sleep
            Thread.sleep(20);
            //point2 after sleep
            System.out.println("Calculating");
            for (int i = 0; i < 900000; i++) {
                d = d + (Math.PI + Math.E) / d;
            }
        }

        } catch (InterruptedException e) {
            System.out.println("Exiting by Exception");
        }

        System.out.println("ATask.run() interrupted!");
    }
}

在point1之前處point2之後發生中斷會產生兩種不同的結果，可以通過修改InterruptTaskTest main()裏的Thread.sleep()的時間來達到在point1之前產生中斷或在point2之後產生中斷.
如果在point1之前發生中斷，程序會在調用Thread.sleep()時拋出InterruptedException從而結束線程．這和在Thread.sleep()時被中斷是一樣的效果.程序運行結果可能如下：

I am running!
Calculating
I am running!
Calculating
I am running!
Calculating
I am running!
****************************
Interrupted Thread!
****************************
Exiting by Exception
ATask.run() interrupted!

如果在point2之後發生中斷，線程會繼續執行到下一次while判斷中斷狀態時．程序運行結果可能如下：

I am running!
Calculating
I am running!
Calculating
I am running!
Calculating
****************************
Interrupted Thread!
****************************
ATask.run() interrupted!