linux多线程学习(六)——信号量实现同步

信号量的互斥同步都是通过PV原语来操作的，我们可以通过注册两个信号量，让它们在互斥的问题上互动，从而达到同步。通过下面实例就可以很容易理解：

 

[cpp] view plain copy

1. #include <stdlib.h>      
2. #include <stdio.h>      
3. #include <unistd.h>      
4. #include <pthread.h>      
5. #include <semaphore.h>      
6. #include <errno.h>      
7.       
8. #define  return_if_fail(p)  if((p) == 0){printf ("[%s]:func error!/n", __func__);return;}      
9.       
10. typedef struct _PrivInfo      
11. {      
12.   sem_t s1;      
13.   sem_t s2;      
14.   time_t end_time;      
15. }PrivInfo;      
16.       
17. static void info_init (PrivInfo* thiz);      
18. static void info_destroy (PrivInfo* thiz);      
19. static void* pthread_func_1 (PrivInfo* thiz);      
20. static void* pthread_func_2 (PrivInfo* thiz);      
21.       
22. int main (int argc, char** argv)      
23. {      
24.   pthread_t pt_1 = 0;      
25.   pthread_t pt_2 = 0;      
26.   int ret = 0;      
27.   PrivInfo* thiz = NULL;      
28.         
29.   thiz = (PrivInfo* )malloc (sizeof (PrivInfo));      
30.   if (thiz == NULL)      
31.   {      
32.     printf ("[%s]: Failed to malloc priv.\n");      
33.     return -1;      
34.   }      
35.       
36.   info_init (thiz);      
37.       
38.   ret = pthread_create (&pt_1, NULL, (void*)pthread_func_1, thiz);      
39.   if (ret != 0)      
40.   {      
41.     perror ("pthread_1_create:");      
42.   }      
43.       
44.   ret = pthread_create (&pt_2, NULL, (void*)pthread_func_2, thiz);      
45.   if (ret != 0)      
46.   {      
47.      perror ("pthread_2_create:");      
48.   }      
49.       
50.   pthread_join (pt_1, NULL);      
51.   pthread_join (pt_2, NULL);      
52.       
53.   info_destroy (thiz);      
54.         
55.   return 0;      
56. }      
57.       
58. static void info_init (PrivInfo* thiz)      
59. {      
60.   return_if_fail (thiz != NULL);      
61.       
62.   thiz->end_time = time(NULL) + 10;      
63.         
64.   sem_init (&thiz->s1, 0, 1);      
65.   sem_init (&thiz->s2, 0, 0);      
66.       
67.   return;      
68. }      
69.       
70. static void info_destroy (PrivInfo* thiz)      
71. {      
72.   return_if_fail (thiz != NULL);      
73.       
74.   sem_destroy (&thiz->s1);      
75.   sem_destroy (&thiz->s2);      
76.       
77.   free (thiz);      
78.   thiz = NULL;      
79.       
80.   return;      
81. }      
82.       
83. static void* pthread_func_1 (PrivInfo* thiz)      
84. {      
85.   return_if_fail (thiz != NULL);      
86.       
87.   while (time(NULL) < thiz->end_time)      
88.   {      
89.     sem_wait (&thiz->s2);      
90.     printf ("pthread1: pthread1 get the lock.\n");      
91.       
92.     sem_post (&thiz->s1);      
93.     printf ("pthread1: pthread1 unlock\n");      
94.       
95.     sleep (1);      
96.   }      
97.       
98.   return;      
99. }      
100.       
101. static void* pthread_func_2 (PrivInfo* thiz)      
102. {      
103.   return_if_fail (thiz != NULL);      
104.       
105.   while (time (NULL) < thiz->end_time)      
106.   {      
107.     sem_wait (&thiz->s1);      
108.     printf ("pthread2: pthread2 get the unlock.\n");      
109.       
110.     sem_post (&thiz->s2);      
111.     printf ("pthread2: pthread2 unlock.\n");      
112.       
113.     sleep (1);      
114.   }      
115.       
116.   return;      
117. }      

pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock
pthread2: pthread2 get the unlock.
pthread2: pthread2 unlock.
pthread1: pthread1 get the lock.
pthread1: pthread1 unlock

通过执行结果后，可以看出，会先执行线程二的函数，然后再执行线程一的函数。它们两就实现了同步。在上大学的时候，虽然对这些概念知道，可都没有实践过，所以有时候时间一久就会模糊甚至忘记，到了工作如果还保持这么一种状态，那就太可怕了。虽然现在外面的技术在不断的变化更新，可是不管怎么变，其核心技术还是依旧的，所以我们必须要打好自己的基础，再学习其他新的知识，那时候再学新的知识也会觉得比较简单的。闲话多说了两句，在下一篇文章中，我们将会实现一个经典的实例回顾这段时间对多线程的学习，那就是消费者和生产者。