16、JUC:Semaphore-计数信号量

学习过程观看视频：[狂神说Java]
https://www.bilibili.com/video/BV1B7411L7tE?p=13
欢迎大家支持噢，很良心的老师了！

java代码示例：

package com.add;

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

/**
 * Created by zjl
 * 2020/11/24
 **/
public class SemaphoreDemo {
    
    

    public static void main(String[] args) {
    
    

        //可以容纳线程的数量，比作停车位用来限流
        Semaphore semaphore = new Semaphore(3);

        for (int i = 1; i <= 6; i++) {
    
    
            final int temp = i;
            new Thread(()->{
    
    
                try {
    
    
                    semaphore.acquire();  //得到
                    System.out.println("第" + temp + "条线程-------获得--------车位");
                    TimeUnit.SECONDS.sleep(1);
                    System.out.println("第" + temp + "条线程+离开+车位");
                } catch (InterruptedException e) {
    
    
                    e.printStackTrace();
                } finally {
    
    
                    semaphore.release();  //释放
                }
            },String.valueOf(i)).start();
        }
    }
}

运行输出结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/bin/java "-javaagent:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=50075:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/tools.jar:/Users/zhangjianlong/testCode/JUC-study/target/classes:/Users/zhangjianlong/apache-maven-3.6.3/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.add.SemaphoreDemo
第1条线程-------获得--------车位
第3条线程-------获得--------车位
第2条线程-------获得--------车位
第3条线程+离开+车位
第2条线程+离开+车位
第1条线程+离开+车位
第4条线程-------获得--------车位
第6条线程-------获得--------车位
第5条线程-------获得--------车位
第5条线程+离开+车位
第6条线程+离开+车位
第4条线程+离开+车位

Process finished with exit code 0

知识点：

semaphore.acquire(); //获得，如果已经满了，等待，等待被释放为止。

semaphore.release(); //释放，会将当前的信号量释放+1，然后唤醒等待的线程。