线程优先级

线程优先级是通过一个int 变量priority来控制的，优先级范围为1到10，可以通过setPriority(int)来设置，优先级默认为5。

以下是一个示例代码，

package thread;

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.TimeUnit;

public class ThreadPriority {

    private static volatile boolean notStart = true;

    private static volatile boolean notEnd   = true;

    public static void main(String[] args) throws Exception {

        List<Job> jobs = new ArrayList<Job>();

        // 先给不同线程分别给一个不同的优先级并执行线程

        for (int i = 0; i < 10; i++) {

            int priority = i < 5 ? Thread.MIN_PRIORITY : Thread.MAX_PRIORITY;

            Job job = new Job(priority);

            jobs.add(job);

            Thread thread = new Thread(job, "Thread:" + i);

            thread.setPriority(priority);// 设置优先级

            thread.start();

        }

        notStart = false;

        TimeUnit.SECONDS.sleep(10);

        notEnd = false;

        for (Job job : jobs) {

            System.out.println("Job priority:" + job.priority + " ,jobCount:" + job.jobCount);

        }

    }

    static class Job implements Runnable {

        // 线程优先级

        private int  priority;

        private long jobCount;

        // 设置优先级

        public Job(int priority) {

            this.priority = priority;

        }

        @Override

        public void run() {

            while (notStart) {// 如果线程是开着的，

                /**

                 * Causes the currently executing thread object to temporarily pause and allow other threads to execute.

                 */

                Thread.yield();// 那么先停下来，让其他线程执行

            }

            while (notEnd) {

                Thread.yield();

                jobCount++;

            }

        }

    }

}

打印出

Job priority:1 ,jobCount:2847305

Job priority:1 ,jobCount:1

Job priority:1 ,jobCount:16654503

Job priority:1 ,jobCount:9022916

Job priority:1 ,jobCount:2847155

Job priority:10 ,jobCount:9517759

Job priority:10 ,jobCount:11989979

Job priority:10 ,jobCount:9069022

Job priority:10 ,jobCount:24185755

Job priority:10 ,jobCount:9519740

由此可以看出，线程的优先级没有生效，很多优先级1和优先级10的job的技术结果并非常相近，没有明显差异，这表示程序正确性不能依赖线程的优先级的高低