juc包之Semaphore使用

一、好言

最好的生活状态不过就是：一个人，安静而丰盛；两个人，温暖而踏实。

二、背景

看《Java并发编程实战》，第五章，代码练习记载下

三、内容

package com.mouse.moon.threaddemo;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Semaphore;
/**
 * Created by Mahone Wu on 2017/6/16.
 */
public class BoundHashSet {
    private  final Set set ;
    private final Semaphore semaphore;
    public BoundHashSet(int bound){
        this.set = Collections.synchronizedSet(new HashSet());
        semaphore = new Semaphore(bound);
    }
    public boolean add(T o) throws  InterruptedException{
        semaphore.acquire();//获取许可
        boolean wasAdd = false;
        try {
            wasAdd = set.add(o);
            return wasAdd;
        }finally {
            if(!wasAdd){
                semaphore.release();
            }
        }
    }
    public boolean remove(Object o){
        boolean wasRemoved = set.remove(o);
        if(wasRemoved){
            semaphore.release();//释放许可
        }
        return wasRemoved;
    }
}

package com.mouse.moon.threaddemo;
/**
 * Created by Mahone Wu on 2017/6/16.
 */
public class Person {
    private String name;
    private String address;
    public Person(String name, String address) {
        this.name = name;
        this.address = address;
    }
}

package com.mouse.moon.threaddemo;

/**
 * Created by Mahone Wu on 2017/6/16.
 */
public class Main {
    public static void main(String[] args)  {

        final Integer permit = 3;

        Person p1 = new Person("a", "a");
        Person p2 = new Person("b", "b");
        Person p3 = new Person("c", "c");
        Person p4 = new Person("d", "d");
        Person p5 = new Person("e", "e");
        BoundHashSet bhs = new BoundHashSet(permit);
        boolean f1 = false;
        try {
            f1 = bhs.add(p1);
        } catch (InterruptedException e) {
            System.out.println("1");
            e.printStackTrace();
        }
        System.out.println(f1);
        boolean f2 = false;
        try {
            bhs.remove(p1);//这里释放，可以自动修改许可permit大小
            f2 = bhs.add(p2);
        } catch (InterruptedException e) {
            System.out.println("2");
            e.printStackTrace();
        }
        System.out.println(f2);

        boolean f3 = false;
        try {
            f3 = bhs.add(p3);
        } catch (InterruptedException e) {
            System.out.println("3");
            e.printStackTrace();
        }
        System.out.println(f3);

        boolean f4 = false;
        try {
            f4 = bhs.add(p4);
        } catch (InterruptedException e) {
            System.out.println("4");
            e.printStackTrace();
        }
        System.out.println(f4);

        boolean f5 = false;
        try {
            f5 = bhs.add(p5);
        } catch (InterruptedException e) {
            System.out.println("5");
            e.printStackTrace();
        }
        System.out.println(f5);
    }
}

可以看见打印了4个true,并且程序还处理执行中，等待释放一直阻塞到有为至。

image.png

image.png