Java 线程池的工作原理

 

 

  

 

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }
    
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             threadFactory, defaultHandler);
    }
    
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              RejectedExecutionHandler handler) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), handler);
    }
    
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

　

 

 

 

 

 

   

 

import java.util.concurrent.*;

public class ThreadPoolDemo {
    private static ExecutorService pool;

    public static void main(String[] args) {
        //创建优先任务队列的线程池，核心线程池只有1个，线程池最大容量为2，空闲线程的存活时间设为1000毫秒，使用优先任务队列，在这种队列下，前面设置为2的maximumPollSize无效了
        pool = new ThreadPoolExecutor(1, 2, 1000, TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>());

        for (int i = 0; i < 10; i++) {
            pool.execute(new ThreadTest(i));
        }
        pool.shutdown();// 线程池中线程执行完毕后，关闭线程池
    }
}

class ThreadTest implements Runnable, Comparable<ThreadTest> {

    private int priority;

    public ThreadTest(int priority) {
        this.priority = priority;
    }

    //当前对象和其他对象做比较，当前优先级大就返回-1，优先级小就返回1,值越小优先级越高
    public int compareTo(ThreadTest o) {
        return this.priority > o.priority ? -1 : 1;
    }

    public void run() {
        try {
            //让线程阻塞，使后续任务进入缓存队列
            Thread.sleep(1000);
            System.out.println("当前第" + this.priority + "条线程执行\tThreadName：" + Thread.currentThread().getName());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}