c++多线程并发 基础入门 --互斥量mutex, 原子变量atomic

1. 没有mutex

#include 
#include 
#include 

int globalVariable = 0;

void task1()
{
    for(int i = 0; i < 1000000; i++)
 	{
        globalVariable++;
        globalVariable--;
    }
}

int main(int argc, const char * argv[]) 
{
    std::thread t1(task1);
    std::thread t2(task1);
    
    t1.join();
    t2.join();
    
    std::cout<<"current value is "< 
xcode, command+r 运行结果为1，本来++和-- ，最后结果为0才对的，但是最后结果为1。
 current value is 1
 Program ended with exit code: 0
 
2. 加上mutex
 
#include 
#include 
#include 

std::mutex mtx;
int globalVariable = 0;

void task1()
{
    for(int i = 0; i < 1000000; i++)
    {
        mtx.lock();
        globalVariable++;
        globalVariable--;
        mtx.unlock();
    }
}

int main(int argc, const char * argv[]) {

    std::thread t1(task1);
    std::thread t2(task1);
    
    t1.join();
    t2.join();
    
    std::cout<<"current value is "< 
xcode, command+r 运行结果为0, 正确。
 current value is 1
 锁之间的代码叫做临界区