27.多线程原子变量

 1 #include <iostream>
 2 #include <thread>
 3 #include <mutex>
 4 #include <atomic>
 5 using namespace std;
 6 
 7 //全局变量会造成冲突,使得结果不正确
 8 //mutex结果正确,速度慢
 9 //atomic 结果正确,速度快
10 
11 
12 //线程安全,多线程访问不冲突
13 //int num = 0;
14 
15 //原子变量
16 atomic_int num(0);
17 
18 mutex m;//互斥
19 
20 void run()
21 {
22     for (int i = 0; i < 100000; i++)
23     {
24         //m.lock();
25         num++;
26         //m.unlock();
27     }
28 }
29 
30 void main()
31 {
32     clock_t start = clock();
33     thread th1(run);
34     thread th2(run);
35     th1.join();
36     th2.join();
37     clock_t end = clock();
38     cout << num << endl;
39     cout << end - start << "ms" << endl;
40     
41     cin.get();
42 }