39.mutex 的lock_guard与unique_lock

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

#define N 100000

mutex g_mutex;

void add(int *p)
{
    for (int i = 0; i < N; i++)
    {
        //拥有mutex所有权,自动加锁自动解锁,读取失败就会一直等待
        //lock_guard<mutex> lgd(g_mutex);
        //unique也能加锁,但是速度比较慢,根据块语句锁定,根据mutex属性能否加锁
        unique_lock<mutex> ulk(g_mutex);
        (*p)++;
    }
}

void main()
{
    int a = 0;
    thread t1(add, &a);
    thread t2(add, &a);
    t1.join();
    t2.join();
    cout << a << endl;
    cin.get();
}