27.多线程原子变量

#include <iostream>
#include <thread>
#include <mutex>
#include <atomic>
using namespace std;

//全局变量会造成冲突,使得结果不正确
//mutex结果正确,速度慢
//atomic 结果正确,速度快


//线程安全,多线程访问不冲突
//int num = 0;

//原子变量
atomic_int num(0);

mutex m;//互斥

void run()
{
    for (int i = 0; i < 100000; i++)
    {
        //m.lock();
        num++;
        //m.unlock();
    }
}

void main()
{
    clock_t start = clock();
    thread th1(run);
    thread th2(run);
    th1.join();
    th2.join();
    clock_t end = clock();
    cout << num << endl;
    cout << end - start << "ms" << endl;
    
    cin.get();
}