JVM守护线程和非守护线程

http://blog.sina.com.cn/s/blog_605f5b4f0100udin.htmlJava有两种Thread：守护线程Daemon和用户线程User。任何线程都可以是守护线程Daemon或者用户线程User，他们几乎每个方面都是相同的，唯一的区别是判断虚拟机何时离开：用户线程：Java虚拟机在它所有非守护线程已经离开后自动离开。守护线程：守

buster2014

1357人浏览 · 2016-12-29 11:51:44

buster2014 · 2016-12-29 11:51:44 发布

http://blog.sina.com.cn/s/blog_605f5b4f0100udin.html

Java有两种Thread：守护线程Daemon和用户线程User。

任何线程都可以是守护线程Daemon或者用户线程User，他们几乎每个方面都是相同的，唯一的区别是判断虚拟机何时离开：

用户线程：Java虚拟机在它所有非守护线程已经离开后自动离开。

守护线程：守护线程是用来服务用户线程的，如果没有其他用户线程在运行，那么就没有可服务对象，也没有理由继续下去。

setDaemon(boolean on)方法可以方便地设置线程Daemon模式，true为Daemon模式，false为User模式。该方法必须在线程启动之前调用，当线程运行时调用时会产生异常。

当你在一个守护线程中产生了其他线程，那么这些新产生的线程不用设置Daemon属性，都将是守护线程。用户线程与此相同。

使用下面的程序来说明：

import static java.lang.System.out;
import static java.lang.System.in;

import java.io.IOException;
public class TestMain4 extends Thread{
public TestMain4(){

}

public void run(){
  for(int i=1;i<=50;i++){
   try{
    Thread.sleep(100);
    out.println("this is in TestMain4");
   }catch(InterruptedException ex){
    ex.printStackTrace();
   }
   out.println("TestMain4:"+i);
  }
}

public static void main(String[] args){
  TestMain4 test=new TestMain4();
  TestMain5 test1=new TestMain4.TestMain5();
  test.setDaemon(false);//用户线程,必须结束后才能退出JVM
  test.start();

  test1.setDaemon(true);//守护线程，不需要结束
  test1.start();
  System.out.println("isDaemon="+test.isDaemon());
  System.out.println("isDaemon="+test1.isDaemon());

  try {
  out.print("the input is: "+in.read());
} catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
}
}

static class TestMain5 extends Thread{
  public TestMain5(){

  }

  public void run(){
   for(int i=1;i<=50;i++){
    try{
     Thread.sleep(1000);
     out.println("this is in TestMain5");
    }catch(InterruptedException ex){
     ex.printStackTrace();
    }
    out.println("TestMain5:"+i);
   }
  }
}
}

结果：

isDaemon=false
isDaemon=true
this is in TestMain4
TestMain4:1
this is in TestMain4
TestMain4:2
this is in TestMain4
TestMain4:3
this is in TestMain4
TestMain4:4
this is in TestMain4
TestMain4:5
this is in TestMain4
TestMain4:6
this is in TestMain4
TestMain4:7
this is in TestMain4
TestMain4:8
this is in TestMain4
TestMain4:9
this is in TestMain5
TestMain5:1
this is in TestMain4
TestMain4:10
this is in TestMain4
TestMain4:11
this is in TestMain4
TestMain4:12
this is in TestMain4
TestMain4:13
this is in TestMain4
TestMain4:14
this is in TestMain4
TestMain4:15
this is in TestMain4
TestMain4:16
this is in TestMain4
TestMain4:17
this is in TestMain4
TestMain4:18
this is in TestMain4
TestMain4:19
this is in TestMain5
TestMain5:2
this is in TestMain4
TestMain4:20
this is in TestMain4
TestMain4:21
5this is in TestMain4
TestMain4:22
this is in TestMain4
TestMain4:23
this is in TestMain4
TestMain4:24
this is in TestMain4
TestMain4:25
this is in TestMain4
TestMain4:26
this is in TestMain4
TestMain4:27

this is in TestMain4
TestMain4:28
the input is: 53this is in TestMain4
TestMain4:29
this is in TestMain5
TestMain5:3
this is in TestMain4
TestMain4:30
this is in TestMain4
TestMain4:31
this is in TestMain4
TestMain4:32
this is in TestMain4
TestMain4:33
this is in TestMain4
TestMain4:34
this is in TestMain4
TestMain4:35
this is in TestMain4
TestMain4:36
this is in TestMain4
TestMain4:37
this is in TestMain4
TestMain4:38
this is in TestMain4
TestMain4:39
this is in TestMain5
TestMain5:4
this is in TestMain4
TestMain4:40
this is in TestMain4
TestMain4:41
this is in TestMain4
TestMain4:42
this is in TestMain4
TestMain4:43
this is in TestMain4
TestMain4:44
6this is in TestMain4
TestMain4:45
this is in TestMain4
TestMain4:46
this is in TestMain4
TestMain4:47