javaSE21/10/4

多线程

线程休眠

• sleep指定当前线程阻塞的毫秒数
• sleep需要抛出InterruptedException
• sleep时间到达后线程进入就绪状态
• sleep可以模拟网络延时，倒计时等
• 每个对象都有一个锁，sleep不会释放锁

模拟网络延时

//模拟网络延时：放大问题的发生概率
public class TestSleep implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i <= 100; i++) {
            System.out.println("正在加载" + i);
            if (i==99){
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        TestSleep testSleep = new TestSleep();
        new Thread(testSleep).start();

    }
}

模拟倒计时

public class TestSleep2 implements Runnable{
    @Override
    public void run() {
        int i = 10;
        while (true){
            System.out.println(i--);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            if (i==0){
                break;
            }
        }
    }

    public static void main(String[] args) {
        TestSleep2 testSleep2 = new TestSleep2();
        new Thread(testSleep2).start();
    }
}

打印系统时间

public class TestSleep2 implements Runnable{
    @Override
    public void run() {
        Date startTime = new Date(System.currentTimeMillis());//获取系统当前时间
        while (true){
            try {
                Thread.sleep(1000);//休眠一秒
                System.out.println(new SimpleDateFormat("HH:mm:ss").format(startTime));//打印系统当前时间
                startTime=new Date(System.currentTimeMillis());//更新时间
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

    public static void main(String[] args) {
        TestSleep2 testSleep2 = new TestSleep2();
        new Thread(testSleep2).start();
    }
}

线程礼让

• 礼让线程，让当前正在执行的线程暂停，但不阻塞
• 将线程从运行状态转为就绪状态
• 让cpu重新调度，礼让不一定成功

public class TestYield implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"开始执行");
        Thread.yield();
        System.out.println(Thread.currentThread().getName()+"执行结束");
    }

    public static void main(String[] args) {
        TestYield testYield = new TestYield();
        new Thread(testYield,"a").start();
        new Thread(testYield,"b").start();
    }
}

线程强制执行（一般不建议使用）

观测线程状态

public class TestState {
    public static void main(String[] args) {
        Thread thread = new Thread(()->{//Lambda表达式，即Runnable实现类
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("结束进程");
            }
        });
        //观察状态
        Thread.State state = thread.getState();
        System.out.println(state);
        thread.start();//开启线程
        state = thread.getState();
        System.out.println(state);
        while (state!=Thread.State.TERMINATED){
            //只要线程不终止，就一直输出状态
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            state = thread.getState();//更新线程状态
            System.out.println(state);
        }
    }
}

线程的优先级

• main方法的默认优先级是5，优先级最小为1，最大为10
• 先设置优先级再执行
• 优先级低只意味着获得调度的概率低

public class Test {
    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);

        t1.start();

        t2.setPriority(2);
        t2.start();

        t3.setPriority(7);
        t3.start();

        t4.setPriority(1);
        t4.start();
    }
}
class MyPriority implements Runnable{
    @Override
    public void run() {
        //输出线程名和线程优先级
        System.out.println(Thread.currentThread().getName()+":"+Thread.currentThread().getPriority());
    }
}