printf的线程安全性以及cout的线程不安全性验证，以及意外收获

#include <iostream>
#include <thread>
#include <atomic>
#include <ctime>
#include <mutex>

using namespace std;
std::atomic_int a;
//int a;
std::mutex _mutex;

void add_() {
	for (int i = 0; i < 10000; i++) {
		_mutex.lock();
		a++;
		_mutex.unlock();
		//printf("%d\n", a);	//这个有点快啊	3.831
		std::cout << a << std::endl;	
		//cout << a << endl;	//有没有std速度差不多
	}
}

int main()
{
    clock_t startTime, endTime;
	
	//add_();	//一条线程空跑：12.753

	//atomic:11.744		下午再测 5.757s
	//上锁：11.954	下午再测 5.891s
	startTime = clock();//计时开始
	std::thread t1(add_);
	std::thread t2(add_);

	t1.join();
	t2.join();
    endTime = clock();//计时结束
    std::cout << "The run time is: " << (double)(endTime - startTime) / CLOCKS_PER_SEC << "s" << std::endl;
    system("pause");
    return 0;
}