Java 学习笔记之 线程Priority

线程Priority:

 

线程可以划分优先级，优先级较高的线程得到的CPU资源较多，也就是CPU优先执行优先级较高的线程对象中的任务。

设置线程优先级有助于帮助“线程规划器”确定在下一次选择哪个线程来优先执行。

线程优先级分为10个等级，1-》10

三个常用等级：

线程优先级继承性：

A线程启动了B线程，则B线程的优先级与A线程是一样的。

public class PriorityInheritThread extends Thread {
    @Override
    public void run() {
        System.out.println("1 Run priority = " +  this.getPriority());
        PriorityInheritThread2 thread2 = new PriorityInheritThread2();
        thread2.start();
    }
}

public class PriorityInheritThread2 extends Thread{
    @Override
    public void run() {
        System.out.println("2 Run priority = " +  this.getPriority());
    }
}
public class ThreadRunMain {
    public static void main(String[] args) {
        testPriorityInheritThread();
    }

    public static void testPriorityInheritThread() {
        System.out.println("Main thread begin priority = " + Thread.currentThread().getPriority());
        Thread.currentThread().setPriority(6);
        System.out.println("Main thread end priority = " + Thread.currentThread().getPriority());
        PriorityInheritThread thread1 = new PriorityInheritThread();
        thread1.start();
    }
}

运行结果：

线程规则性：

优先级高的线程总是大部分先执行完。

线程随机性：

当线程优先等级差距很大，谁先执行完和Main线程代码的调用顺序无关。优先级高的线程也不一定每一次都先执行完。

public class RunFastThreadA extends Thread {
    private int count = 0;

    public int getCount() {
        return count;
    }

    @Override
    public void run() {
        while(true){
            count ++;
        }
    }
}

public class RunFastThreadB extends Thread {
    private int count = 0;

    public int getCount() {
        return count;
    }

    @Override
    public void run() {
        while(true){
            count ++;
        }
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testRunFastThread();
    }

    public static void testRunFastThread() {
        try {
            RunFastThreadA a = new RunFastThreadA();
            a.setPriority(Thread.NORM_PRIORITY - 3);
            a.start();
            RunFastThreadB b = new RunFastThreadB();
            b.setPriority(Thread.NORM_PRIORITY + 3);
            b.start();
            Thread.sleep(10000);
            a.stop();
            b.stop();
            System.out.println("a = " + a.getCount());
            System.out.println("b = " + b.getCount());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：