java多线程系列7-停止线程
本文主要总结在java中停止线程的方法
在java中有以下三种方法可以终止正在运行的线程:
1、使用退出标志
2、使用stop方法强行终止线程,但是不推荐,因为stop和suspend、resume一样都是过时的方法
3、使用interrup方法中断线程
停止不了的线程
本例将使用interrupt方法来停止进程,看看效果:
public class MyThread extends Thread { @Override public void run() { super.run(); for (int i = 0; i < 1234; i++) { System.out.println("i=" + (i + 1)); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(2000); thread.interrupt(); } catch (InterruptedException e) { System.out.println("main catch"); e.printStackTrace(); } } }
可以看出,线程没有停止
判断线程是否是停止状态
在java的SDK中,Thread.java类里提供了两种方法:
(1)this.interrupted():测试当前线程是否已经中断
(2)this.isInterrupted():测试线程是否已经中断
首先看一下interrupted()
实战验证一下:
public class MyThread extends Thread { @Override public void run() { super.run(); for (int i = 0; i < 10000; i++) { System.out.println("i=" + (i + 1)); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(1000); thread.interrupt(); System.out.println("是否停止1?="+thread.interrupted()); System.out.println("是否停止2?="+thread.interrupted()); } catch (InterruptedException e) { System.out.println("main catch"); e.printStackTrace(); } System.out.println("end!"); } }
运行结果如下:
.......................
i=9998
i=9999
i=10000
是否停止1?=false
是否停止2?=false
end!
由于interrupted是测试当前线程,当前线程为main,一直没有中断,所以返回两个false
将代码修改一下:
public class Run { public static void main(String[] args) { Thread.currentThread().interrupt(); System.out.println("是否停止1?=" + Thread.interrupted()); System.out.println("是否停止2?=" + Thread.interrupted()); System.out.println("end!"); } }
返回如下信息:
是否停止1?=true
是否停止2?=false
end!
由于interrupted方法有清除状态的功能,所以第二次返回false
再看看isInterrupted()方法
public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(1000); thread.interrupt(); System.out.println("是否停止1?=" + thread.isInterrupted()); System.out.println("是否停止2?=" + thread.isInterrupted()); } catch (InterruptedException e) { System.out.println("main catch"); e.printStackTrace(); } System.out.println("end!"); } }
运行结果:
i=123367
i=123368
是否停止1?=true
是否停止2?=true
i=123369
i=123370
i=123371
i=123372
总结:
(1)this.interrupted():测试当前线程是否已经中断,执行后具有将状态标志清除为false的功能
(2)this.isInterrupted():测试线程是否已经中断,但不清除状态标志
能停止的线程--异常法
可以在线程中用for语句来判断一下线程是否是停止状态,如果是停止状态,则后面的代码不再运行即可
public class MyThread extends Thread { @Override public void run() { super.run(); try { for (int i = 0; i < 500000; i++) { if (this.interrupted()) { System.out.println("已经是停止状态了,我要退出了!"); throw new InterruptedException(); } System.out.println("i=" + (i + 1)); } System.out.println("我在for下面"); } catch (InterruptedException e) { System.out.println("进MyThread.java类run方法中的catch了!"); e.printStackTrace(); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(2000); thread.interrupt(); } catch (InterruptedException e) { System.out.println("main catch"); e.printStackTrace(); } System.out.println("end!"); } }
在sleep中停止
如果线程在sleep状态下停止线程,有什么效果呢?
public class MyThread extends Thread { @Override public void run() { super.run(); try { System.out.println("run begin"); Thread.sleep(200000); System.out.println("run end"); } catch (InterruptedException e) { System.out.println("在沉睡中被停止!进入catch!" + this.isInterrupted()); e.printStackTrace(); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(200); thread.interrupt(); } catch (InterruptedException e) { System.out.println("main catch"); e.printStackTrace(); } System.out.println("end!"); } }
运行结果:
run begin
end!
在沉睡中被停止!进入catch!false
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at com.wuyudong.test1.MyThread.run(MyThread.java:9)
结果说明如果在sleep状态下停止线程,会进入catch语句,并且清除停止状态值,使之变成false
下面进行相反的操作,修改一下:
public class MyThread extends Thread { @Override public void run() { super.run(); try { for (int i = 0; i < 100000; i++) { System.out.println("i=" + (i + 1)); } System.out.println("run begin"); Thread.sleep(200000); System.out.println("run end"); } catch (InterruptedException e) { System.out.println("先停止,再遇到了sleep!进入catch!"); e.printStackTrace(); } } } public class Run { public static void main(String[] args) { MyThread thread = new MyThread(); thread.start(); thread.interrupt(); System.out.println("end!"); } }
运行结果如下:
i=100000
run begin
先停止,再遇到了sleep!进入catch!
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at com.wuyudong.test1.MyThread.run(MyThread.java:12)
能停止的线程--暴力停止
使用stop方法停止线程是十分暴力的
public class MyThread extends Thread { private int i = 0; @Override public void run() { super.run(); try { while (true) { i++; System.out.println("i=" + i); Thread.sleep(1000); } } catch (InterruptedException e) { System.out.println("先停止,再遇到了sleep!进入catch!"); e.printStackTrace(); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(8000); thread.stop(); } catch (Exception e) { e.printStackTrace(); } } }
运行结果如下:
i=1
i=2
i=3
i=4
i=5
i=6
i=7
i=8
方法stop与异常
调用stop方法的时候会抛出java.lang.ThreadDeath异常,但是通常此异常不需要显式地捕捉
public class MyThread extends Thread { private int i = 0; @Override public void run() { super.run(); try { while (true) { i++; System.out.println("i=" + i); Thread.sleep(1000); } } catch (InterruptedException e) { System.out.println("先停止,再遇到了sleep!进入catch!"); e.printStackTrace(); } } } public class Run { public static void main(String[] args) { try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(8000); thread.stop(); } catch (Exception e) { e.printStackTrace(); } } }
使用return停止线程
将方法interrupt与return结合使用也能实现停止线程的效果
public class MyThread extends Thread { private int i = 0; @Override public void run() { super.run(); while(true){ if(this.isInterrupted()){ System.out.println("停止了!"); return; } System.out.println("timer="+System.currentTimeMillis()); } } } public class Run { public static void main(String[] args) throws InterruptedException{ try { MyThread thread = new MyThread(); thread.start(); Thread.sleep(2000); thread.interrupt(); } catch (Exception e) { e.printStackTrace(); } } }
运行结果如下:
timer=1452841019023
timer=1452841019023
timer=1452841019023
timer=1452841019023
停止了!