2022.10.15线程状态观测

线程状态观测

线程优先级

package com.fei.stata;
​
public class TestPriority extends Thread{
    public static void main(String[] args) {
        System.out.println(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);
        //先设置优先级在启动
        t1.start();
        t2.setPriority(5);
        t2.start();
        t3.setPriority(Thread.MAX_PRIORITY);
        t3.start();
        t4.setPriority(9);
        t4.start();
        t5.setPriority(4);
        t5.start();
        t6.setPriority(6);
        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，后台记录操作日志，监控内存，垃圾回收等待

package com.fei.stata;
​
public class TestDaemon {
    public static void main(String[] args) {
        You you = new You();
        God god = new God();
        Thread thread = new Thread(god);
        thread.setDaemon(true);//默认是False表示是用户线程，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();//you 你用户线程启动
​
​
​
    }
}
//上帝
class God implements Runnable{
    @Override
    public void run() {
        while (true){
            System.out.println("上帝保佑着你");
        }
​
    }
}
//你
class You implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("你活的很开心");
        }
        System.out.println("Goodbye");
​
    }
}
​

线程同步

三大不安全案例

package com.fei.syn;
​
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
        new Thread(buyTicket,"晋儒").start();
        new Thread(buyTicket,"小宪").start();
        new Thread(buyTicket,"海朋").start();
    }
}
class BuyTicket implements Runnable{
    private int ticketNums = 10;
    boolean flag = true;//外部停止方式
    @Override
    public void run() {
        //买票
        while (flag){
            try {
                buy();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
​
    }
    //synchronized:同步方法，上锁只允许一个线程执行，其他线程阻塞
    private synchronized void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNums<=0){
            flag = false;
            return;
        }
        Thread.sleep(100);
        //买票
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
    }
}