42.死锁

 1 #include <iostream>
 2 #include <thread>
 3 #include <mutex>
 4 using namespace std;
 5 
 6 #define COUNT 100000
 7 
 8 mutex g_mutex1, g_mutex2;//互斥量
 9 
10 void add1(int *a, int *b)
11 {
12     for (int i = 0; i < COUNT; i++)
13     {
14         g_mutex1.lock();
15         (*a)++;
16         
17 
18         g_mutex2.lock();
19         (*b)++;
20         
21         g_mutex2.unlock();
22         g_mutex1.unlock();
23     }
24 }
25 
26 void add2(int *a, int *b)
27 {
28     for (int i = 0; i < COUNT; i++)
29     {
30         g_mutex2.lock();
31         g_mutex1.lock();
32         (*a)++;
33         g_mutex1.unlock();
34         (*b)++;
35         g_mutex2.unlock();
36     }
37 }
38 
39 void main()
40 {
41     int a = 0;
42     int b = 0;
43     thread th1(add1, &a, &b);
44     thread th2(add2, &a, &b);
45 
46     while (1)
47     {
48         cout << a << endl;
49         cout << b << endl;
50         this_thread::sleep_for(chrono::seconds(2));
51     }
52 }

要想解决死锁就需要lock与unlock成对使用,不允许连续使用两个lock

 1 #include <iostream>
 2 #include <thread>
 3 #include <mutex>
 4 using namespace std;
 5 
 6 #define COUNT 100000
 7 
 8 mutex g_mutex1, g_mutex2;//互斥量
 9 
10 void add1(int *a, int *b)
11 {
12     for (int i = 0; i < COUNT; i++)
13     {
14         g_mutex1.lock();
15         (*a)++;
16         g_mutex1.unlock();
17 
18         g_mutex2.lock();
19         (*b)++;
20         g_mutex2.unlock();
21         
22     }
23     cout << "end" << endl;
24 }
25 
26 void add2(int *a, int *b)
27 {
28     for (int i = 0; i < COUNT; i++)
29     {
30         
31         g_mutex1.lock();
32         (*a)++;
33         g_mutex1.unlock();
34         g_mutex2.lock();
35         (*b)++;
36         g_mutex2.unlock();
37         
38     }
39     cout << "end" << endl;
40 }
41 
42 void main()
43 {
44     int a = 0;
45     int b = 0;
46     thread th1(add1, &a, &b);
47     thread th2(add2, &a, &b);
48 
49     while (1)
50     {
51         cout << a << endl;
52         cout << b << endl;
53         this_thread::sleep_for(chrono::seconds(1));
54     }
55 }