多线程-并发基础

高并发： High Concurrency

CPU 多级缓存： 数据 存取 通过高速缓存 cache。一级缓存 二级缓存 三级缓存

时间局部性  空间局部性

缓存一致性 MESI （修改  独享 共享 无效） 

乱序执行优化

 

JAVA虚拟机-内存模型 JMM

堆： 用户对象信息存储

栈： 对象引用、基本类型变量存储，堆区对象的私有拷贝

 

import com.imooc.concurrency.annoations.NodThreadSafe;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

@NodThreadSafe
public class ConcurrentyTest {

    // 请求总数
    public static int countTotle = 5000;
    // 并发执行线程数
    public static int threadTotle = 200;
    public static int sum = 0;

    public static void main(String[] args)throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool(); //线程池
        final Semaphore semaphore = new Semaphore(threadTotle);             //信号量
        final CountDownLatch countDownLatch = new CountDownLatch(countTotle); // 计数器
        for (int i=0;i<countTotle ;i++){
            executorService.execute(() ->{
                try {
                    semaphore.acquire(); // 是否允许被执行
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                countDownLatch.countDown();//计数器 -1
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        System.out.println(sum);
    }

    private static void add() {
        sum++;
    }
}