Java线程的优先级

线程优先级

• Java提供一个线程调度器来监控程序中启动后进入就绪状态的所有线程，线程调度器按照优先级决定应该调度哪个线程来执行。
• 线程的优先级用数字表示，范围从1~10

Thread.MIN_PRIORITY = 1;
Thread.MAX_PRIORITY = 10;
Thread.NORM_PRIORITY = 5;

• 使用以下方式改变或获取优先级

  getPriority().setPriority(int xxx)
  

优先级的设定建议在start()高度前

优先级低只是意味着获得调度的概率低，并不是优先级低就不会被调用了，这都是看CPU的调度

package com.xiao.state;

//测试线程的优先级
public class TestPriority extends Thread{

    public static void main(String[] args) {
        //主线程默认优先线
        System.out.printf(Thread.currentThread().getName()+"---"+Thread.currentThread().getPriority());

        MyPriority myPriority = new MyPriority();

        Thread t1 = new Thread(myPriority);
        Thread t2 = new Thread(myPriority);
        Thread t3 = new Thread(myPriority);
        Thread t4 = new Thread(myPriority);
        Thread t5 = new Thread(myPriority);
        Thread t6 = new Thread(myPriority);

        //先设置优先级，再启动
        t1.start();

        t2.setPriority(1);
        t2.start();

        t3.setPriority(4);
        t3.start();

        t4.setPriority(Thread.MAX_PRIORITY);
        t4.start();

//        t5.setPriority(-1);
//        t5.start();
//
//        t6.setPriority(11);
//        t6.start();

    }

}
class MyPriority implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"---"+Thread.currentThread().getPriority());
    }
}

守护（daemon）线程

• 线程分为用户线程和守护线程
• 虚拟机必须确保用户线程执行完毕
• 虚拟机不用等待守护线程执行完毕
• 如，后台记录操作日记，监控内存，垃圾回收等待...

package com.xiao.state;

//测试守护线程
//上帝守护你
public class TestDaemon {

    public static void main(String[] args) {
        God god = new God();
        You you = new You();

        Thread thread = new Thread(god);
        thread.setDaemon(true); //默认是false表示是用心线程，正常的线程都是用户线程...
        thread.start(); //上帝守护线程启动
        new Thread(you).start(); //你用户线程启动

    }
    
}

//上帝
class God implements Runnable{
    @Override
    public void run() {
        while (true){
            System.out.println("上帝保护着你");
        }
    }
}

class You implements Runnable{

    @Override
    public void run() {
        for (int i = 0; i < 2650; i++) {
            System.out.println("一生都开心");
            
        }
        System.out.println("=====goodbye! world====");
    }
}

线程优先级和守护线程