线程优先级

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
• 可以使用个体Priority()查看线程的优先级，setPriority(int)设置线程的优先级

源码

 /**
  * The minimum priority that a thread can have.
  */
 public final static int MIN_PRIORITY = 1;

/**
  * The default priority that is assigned to a thread.
  */
 public final static int NORM_PRIORITY = 5;

 /**
  * The maximum priority that a thread can have.
  */
 public final static int MAX_PRIORITY = 10;

public final void setPriority(int newPriority) {
    ThreadGroup g;
    checkAccess();
    if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
        throw new IllegalArgumentException();
    }
    if((g = getThreadGroup()) != null) {
        if (newPriority > g.getMaxPriority()) {
            newPriority = g.getMaxPriority();
        }
        setPriority0(priority = newPriority);
    }
}

/**
 * Returns this thread's priority.
 *
 * @return  this thread's priority.
 * @see     #setPriority
 */
public final int getPriority() {
    return priority;
}

例子

package MultiProcess;

//测试线程的优先级
public class TestPriority extends Thread{
    public static void main(String[] args) {
        //主线程默认优先级
        System.out.println(Thread.currentThread().getName() + "-->" +
                Thread.currentThread().getPriority());

        MyPriority myPriority = new MyPriority();

        Thread thread1 = new Thread(myPriority);
        Thread thread2 = new Thread(myPriority);

        thread1.setPriority(2);
        thread2.setPriority(8);

        thread1.start();
        thread2.start();

    }
}

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

结果
main-->5
Thread-1-->8
Thread-0-->2