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（start）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（优先级高的先调度）。使用getPriority()方法来获取优先级，使用setPriority(int x)方法来改变优先级。

线程的优先级用数字表示，范围从1~10
Thread.MIN_PRIORITY = 1;
Thread.NORM_PRIORITY = 5;
Thread.MAX_PRIORITY = 10;

public class TestPriority {
    public static void main(String[] args) {
        //主线程优先级
        System.out.println(Thread.currentThread().getName()+"--优先级--"+Thread.currentThread().getPriority());

        MyPriority myPriority = new MyPriority();

        Thread t0 = new Thread(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);

        //先设置优先级，再启动
        System.out.println("\n----默认优先级----");
        t1.start();//启动线程，并不会立即执行，等待CPU的调度
        System.out.println("----默认优先级----\n");
        t2.setPriority(3);
        t2.start();

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

        t4.setPriority(Thread.MAX_PRIORITY);//最大优先级
        t4.start();

        t5.setPriority(Thread.MIN_PRIORITY);//最小优先级
        t5.start();

        t0.setPriority(15);//会报错
        t0.start();

    }

}

class MyPriority implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+"--优先级--"+Thread.currentThread().getPriority());
    }
}

运行结果：

main--优先级--5

----默认优先级----
Thread-1--优先级--5
----默认优先级----

Thread-2--优先级--3
Thread-3--优先级--7
Thread-4--优先级--10
Thread-5--优先级--1
Exception in thread "main" java.lang.IllegalArgumentException
	at java.lang.Thread.setPriority(Thread.java:1089)
	at com.study.多线程.demo2.TestPriority.main(TestPriority.java:34)

Process finished with exit code 1

从中我们可以发现，main线程的优先级为5，线程的默认优先级也是5。因为代码量太少，在运行结果中并没有按照优先级高低来执行。所以说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，得看CPU的调度。