pthread_cleanup_push与pthread_cleanup_pop

zjw0722

apue p295的代码，讲解pthread_cleanup_push和pthread_cleanup_pop的使用，有个地方不太明白，求解释一下。

代码：

1. #include <stdio.h>
   
2. #include <pthread.h>
   
3. 
   
4. void cleanup(void *arg)
   
5. {
   
6.     printf("cleanup : %s \n", (char*)arg);
   
7. }
   
8. 
   
9. void *thr_fn1(void *arg)
   
10. {
    
11.     printf("thread 1 start \n");
    
12.     pthread_cleanup_push(cleanup, const_cast<char*>("thread 1 first handler"));
    
13.     pthread_cleanup_push(cleanup, const_cast<char*>("thread 1 second handler"));
    
14.     printf("thread 1 push complete\n");
    
15. 
    
16.     if (arg)
    
17.     {
    
18.         return ((void*)1);
    
19.     }
    
20.     pthread_cleanup_pop(0);
    
21.     pthread_cleanup_pop(0);
    
22.     return ((void*)1);
    
23. }
    
24. 
    
25. void *thr_fn2(void *arg)
    
26. {
    
27.     printf("thread 2 start\n");
    
28.     pthread_cleanup_push(cleanup, const_cast<char*>("thread 2 first handler"));
    
29.     pthread_cleanup_push(cleanup, const_cast<char*>("thread 2 second handler"));
    
30.     printf("thread 2 push complete\n");
    
31.     if (arg)
    
32.     {
    
33.         pthread_exit((void*)2);
    
34.     }
    
35.     pthread_cleanup_pop(0);
    
36.     pthread_cleanup_pop(0);
    
37.     pthread_exit((void*)2);
    
38. }
    
39. 
    
40. int main(int argc, char **argv)
    
41. {
    
42.     pthread_t tid1, tid2;
    
43.     void *tret;
    
44. 
    
45.     pthread_create(&tid1, NULL, thr_fn1, (void*)1);
    
46.     pthread_create(&tid2, NULL, thr_fn2, (void*)1);
    
47. 
    
48.     pthread_join(tid1, &tret);
    
49.     printf("thread 1 exit code %ld\n", (long)tret);
    
50. 
    
51.     pthread_join(tid2, &tret);
    
52.     printf("thread 2 exit code %ld\n", (long)tret);
    
53. 
    
54.     return 0;
    
55. }
    

复制代码

有些不太明白的地方是：
1、书上说了，如果以0调用pthread_cleanup_push，则清理函数不会被调用，且不论以什么方式调用，pthread_cleanup_pop都会删除上次pthread_cleanup_push调用建立的清理函数。