JDK源码——CountDownLatch/CyclicBarrier/Semaphore类

让一些线程阻塞直到另一些线程完成一系列操作后才被唤醒，CountDownLatch主要有两个方法，当一个或多个线程调用await方法时，调用线程会被阻塞。其它线程调用countDown方法会将计数器减1(调用countDown方法的线程不会阻塞)，当计数器的值变为零时，因调用await方法被阻塞的线程会被唤醒，继续执行。

package com.zhuangxiaoyan.jdk.juc.JucLock;

import java.util.concurrent.CountDownLatch;


public class CountDownLatchDemo {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(6);

        for (int i = 1; i <= 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "t 上完自习室 离开教室");
                countDownLatch.countDown();
            }, String.valueOf(i)).start();
        }
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + "t……班长最后走人");
    }
}

package com.zhuangxiaoyan.jdk.juc.JucLock;

import java.util.concurrent.CountDownLatch;


public class CountDownLatchDemo {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(6);

        for (int i = 1; i <= 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "t 国 ，被灭");
                countDownLatch.countDown();
            }, Countryenum.forEach_counttryEnum(i).getRetMessage()).start();
        }
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + "t……秦帝国统一天下");
    }
}



package com.zhuangxiaoyan.jdk.juc.JucLock;

import lombok.Getter;


public enum Countryenum {

    ONE(1, "齐"), TWO(2, "楚"), THREE(3, "燕"), FOUR(4, "赵"), FIVE(5, "魏"), SIX(6, "韩");
    @Getter
    private Integer retcode;
    @Getter
    private String retMessage;

    Countryenum(Integer retcode, String retMessage) {
        this.retcode = retcode;
        this.retMessage = retMessage;
    }

    public static Countryenum forEach_counttryEnum(int index){
        Countryenum[] values = Countryenum.values();
        for (Countryenum element:values){
            if (index==element.getRetcode()){
                return element;
            }
        }
        return null;
    }
}

package com.zhuangxiaoyan.jdk.juc.JucLock;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;


public class CyclicBarrierDemo {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier=new CyclicBarrier(7,()->{
            System.out.println("^^^^^^^召唤神龙");
        });
        for (int i=1;i<=7;i++){
            final int Temp=i;
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"t 收集到了第"+Temp+"龙珠");
                try {
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    e.printStackTrace();
                }
            },String.valueOf(i)).start();
        }
    }
}

信号量主要用于两个目的，一个是用于多个共享资源的互斥使用，另一个用于并发线程数的控制。

package com.zhuangxiaoyan.jdk.juc.JucLock;

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


public class SemaphoreDemo {

    public static void main(String[] args) {
        Semaphore semaphore=new Semaphore(3);

        for (int i=1;i<=6;i++){
            new Thread(()->{
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName()+"t抢到车位");
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    }catch (InterruptedException e){
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName()+"t停车3秒后离开车位");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    semaphore.release();
                }
            },String.valueOf(i)).start();
        }
    }
}