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<>();
        // 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。