家人再也不用担心我面试了（一），并发系列之闭锁、栅栏以及信号量

首先记下：闭锁和栅栏是通过线程数+await()方法实现的，而闭锁有一个countDown()方法来减线程数；栅栏是可以循环使用的

           信号量是通过许可证数+acquire()+release()方法实现的。

1.闭锁场景：通过CountDownLatch的构造方法中的parties，通过每次执行countDown()方法，等计数器减为0后,await()方法不再阻塞，继续往下运行其他内容。（三人同时去吃饭，并行三个线程，最后一起吃饭）

new CountDownLatch(2);
//设置计数器为2
 countDownLatch.countDown();
 // 计数器减一
countDownLatch.await();
//是否计数器未0，如果是等待其他线程执行完毕
//后在执行main线程里的其他方法;

2.栅栏场景：所有线程互相等待，直到所有线程都到达某一点时才打开栅栏，然后线程继续执行。（学生刷卡后等待，一块放学回家；或者3人一组回家）

Thread.sleep(500); // 执行到这里睡眠500ms

cyclicBarrier.await(); //等待其他的栅栏工作线程 //执行到这里 //才会继续往下执行

3.信号量场景：车库人员管理车辆进出

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以下例子是搜集各个地方地方汇集的，有部分修改：以下代码是为了自学，如有侵权可能，请联系我删除

package com.zrtl.tms.today.controller;

import java.util.concurrent.CountDownLatch;

/**
          闭锁
 * Created by adminstrator on 2020/5/21.
 */
public class Test {

   private static CountDownLatch latch = new CountDownLatch(3);

    public static void main(String[] args) {
        new Thread(){
            @Override
            public void run(){
                System.out.println("father is coming");
                latch.countDown();
            }
        }.start();

        new Thread(){
            @Override
            public void run(){
                System.out.println("mother is coming");
                latch.countDown();
            }
        }.start();

        new Thread(){
            @Override
            public void run(){
                System.out.println("i am coming");
                latch.countDown();
            }
        }.start();

        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("all together");
    }

}

 

package com.zrtl.tms.today.controller;

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

/**
  栅栏
 * Created by adminstrator on 2020/5/21.
 */
public class Test3 {
    private final int STUDENT_COUNT = 15;

    final CyclicBarrier cyclicBarrier = new CyclicBarrier(5,
            new Runnable() {
                @Override
                public void run() {
                    System.out.println("5个学生可以放行");
                }
            }
    );

    private void goHome() throws BrokenBarrierException, InterruptedException {
        System.out.println(Thread.currentThread().getName()+"学生已刷卡等待回家");
        cyclicBarrier.await();
//        System.out.println(Thread.currentThread().getName()+"回家了");
    }

    public static void main(String[] args) throws InterruptedException {
        final Test3 instance = new Test3();
        int j = 0;
        for(int i=0;i

 

package com.zrtl.tms.today.controller;

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

/**
     信号量
 * Created by adminstrator on 2020/5/21.
 */
public class TestSemaphore {

    private static final Semaphore semaphore = new Semaphore(1);
    private static final ThreadPoolExecutor threadPool = new ThreadPoolExecutor(
            5,10,60, TimeUnit.SECONDS,new LinkedBlockingDeque()
            );

    private static class InformationThread extends Thread{
        private final String name;
        private final int age;

        public InformationThread(String name,int age){
            this.name = name;
            this.age = age;
        }

        @Override
        public void run(){
            try {
                semaphore.acquire();
                System.out.println(Thread.currentThread().getName()+":大家好，我是"+name+"我今年"+age+"岁当前时间为："+System.currentTimeMillis());

                Thread.sleep(1000);

                System.out.println(name+"要准备释放许可证了，当前时间为："+System.currentTimeMillis());
                semaphore.release();

                System.out.println("当前可使用的许可数为："+semaphore.availablePermits());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args){
        String[] name = {"黎明","王五","张杰","王强","赵二","李四","张三"};
        int[] age={26,27,33,45,19,23,41};
        for(int i=0;i<7;i++){
            Thread t1 = new InformationThread(name[i],age[i]);
            threadPool.execute(t1);
        }
    }


}