Semaphore Java控制并发

川长思鸟来 2022-04-05 09:50 262阅读 0赞

前有CountDownLatch模拟并发[https://blog.csdn.net/weixin\_38336658/article/details/81624539][https_blog.csdn.net_weixin_38336658_article_details_81624539]

这一篇讲下Semaphore,可以完成synchorized实现不了的限流功能。

它有几个函数

semaphore.acquire();

拿到一个信号量

semaphore.release();

释放一个信号量

Semaphore semaphore=new Semaphore(10);

10代表有10个信号量，拿完就没有了，会阻塞进行等待释放

注意一点用多线程验证Semaphore的时候，只能存在一个Semaphore，才可以控制并发流量，多个的话就没有意思了。

下面是一个demo：

package com.example.demo.SeMaPhoreTest;
    
    import java.util.Date;
    import java.util.concurrent.Semaphore;
    
    public class MyThread extends Thread{
    
        Semaphore semaphore;
    
        public MyThread(Semaphore semaphore) {
            this.semaphore=semaphore;
        }
    
        @Override
        public void run() {
            super.run();
            try {
                semaphore.acquire();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("start:"+Thread.currentThread().getName()+" "+new Date());
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("end:"+Thread.currentThread().getName()+" "+new Date());
    
            semaphore.release();
        }
    }

package com.example.demo.SeMaPhoreTest;
    
    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.Semaphore;
    
    public class Test {
    
        static CountDownLatch countDownLatch=new CountDownLatch(100);
    
        public static void main(String[] args) {
    
            Semaphore semaphore=new Semaphore(10);
    
            for(int i=0;i<100;i++){
                //System.out.println(i);
                countDownLatch.countDown();
                Thread thread=new MyThread(semaphore);
                thread.start();
            }
    
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
    }

[https_blog.csdn.net_weixin_38336658_article_details_81624539]: https://blog.csdn.net/weixin_38336658/article/details/81624539