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 = ; 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 = ;
     thread t1(add, &a);
     thread t2(add, &a);
     t1.join();
     t2.join();
     cout << a << endl;
     cin.get();
 }