第三节. 并发编程之Tools+countDownLatch+Semaphore

JUC编程Tools

包含五个工具类： Excutors、Semaphore、Exchanger、CyclicBarrier、CountDownLatch 

Semaphore

            用于流量控制，限制最大的并发的并发访问数。公共资源池定义 X 个permit
            共享锁，非公平锁   ===>   STATE(AQS)

 

 

Semaphore 常用方法

　　Semaphore semaphore  = new Semaphore(2);

　　void semaphore.acquire(); 

　　/* @param permits the number of permits to acquire
 　　* @param timeout the maximum time to wait for the permits
 　　* @param unit the time unit of the {@code timeout} argument */ 

　　semaphore.tryAcquire(1, 1000, TimeUnit.MILLISECONDS);

　　semaphore.release();

举例 

SemaphoreSample.java

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

/**
 * @description :可用于流量控制，限制最大的并发访问数
 */
public class SemaphoreSample {

    public static void main(String[] args) {
        Semaphore semaphore = new Semaphore(2);
        for (int i=0;i<5;i++){
            new Thread(new Task(semaphore,"yangguo+"+i)).start();
        }
    }

    static class Task extends Thread{
        Semaphore semaphore;

        public Task(Semaphore semaphore,String tname){
            this.semaphore = semaphore;
            this.setName(tname);
        }

        public void run() {
            try {
                // semaphore.tryAcquire(1,  1000, TimeUnit.MILLISECONDS);
                semaphore.tryAcquire();
                System.out.println(Thread.currentThread().getName()+":aquire() at time:"+System.currentTimeMillis());

                Thread.sleep(1000);
                semaphore.release();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }
}

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