pthread_clean_push与pthread_cleanup_pop函数详解

#include
void pthread_cleanup_push(void( *fn)(void*)),(void* arg))

void pthread_cleanup_pop(int excute)

这 两个函数可以安排执行线程退出后需要执行的清理函数，这两个函数和进程退出时的atexit很像。

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#include
atexit(void(*fn)(void ))；

“线程取消函数”即线程被取消或者下面描述的情况发生时自动调用的函数。它一般用于释放一些资源，比如释放锁，以免其它的线程永远 也不能获得锁，而造成死锁。
pthread_cleanup_push()函数执行压栈清理函数的操作，而pthread_cleanup_pop()函数执行从栈中删除清理函数的操作。

在下面三种情况下，pthread_cleanup_push()压栈的“清理函数”会被调用：
1, 线程调用pthread_exit()函数，而不是直接return.
2, 响应取消请求时，也就是有其它的线程对该线程调用pthread_cancel()函数。
3, 本线程调用pthread_cleanup_pop()函数，并且其参数非0
注意：
1.当pthread_cleanup_pop()函数的参数为0时，仅仅在线程调用pthread_exit函数或者其它线程对本线程调用 

     pthread_cancel函数时，才在弹出“清理函数”的同时执行该“清理函数”。
2.注意pthread_exit终止线程与线程直接return终止线程的区别,调用return函数是不会在弹出“清理函数”的同时执行该“清理函数的。
3 .pthread_cleanup_push()函数与pthread_cleanup_pop()函数必须成对的出现在同一个函数中。
例子1.：

1. include <pthread.h>
   
2. #include <sys/types.h>
   
3. #include <stdio.h>
   
4. #include <stdlib.h>
   
5. #include <unistd.h>
   
6. #include <errno.h>
   
7. 
   
8. #define handle_error_en(en, msg) \
   
9. do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
   
10. 
    
11. static int done = 0;
    
12. static int cleanup_pop_arg = 0;
    
13. static int cnt = 0;
    
14. 
    
15. static void cleanup_handler(void *arg)
    
16. {
    
17.         printf("Called clean-up handler\n");
    
18.         cnt = 0;
    
19. }
    
20. 
    
21. static void *thread_start(void *arg)
    
22. {
    
23.         time_t start, curr;
    
24. 
    
25.         printf("New thread started\n");
    
26.         pthread_cleanup_push(cleanup_handler, NULL);
    
27.         curr = start = time(NULL);
    
28.         while(!done){
    
29.                 pthread_testcancel(); /* A cancellation point */
    
30.                 if(curr < time(NULL)){
    
31.                         curr = time(NULL);
    
32.                         printf("cnt = %d\n", cnt); /* A cancellation point */
    
33.                         cnt++;
    
34.                 }
    
35.         }
    
36. 
    
37.         pthread_cleanup_pop(cleanup_pop_arg);
    
38.         return NULL;
    
39. }
    
40. 
    
41. int main(int argc, char *argv[])
    
42. {
    
43.         pthread_t thr;
    
44.         void *res;
    
45. 
    
46.         pthread_create(&thr, NULL, thread_start, NULL);
    
47.         sleep(2); /* Allow new thread to run a while */
    
48. 
    
49.         if(argc > 1){
    
50.                 if(argc > 2)
    
51.                         cleanup_pop_arg = atoi(argv[2]);
    
52.                 done = 1;
    
53. 
    
54.         }else{
    
55.                 printf("Canceling thread\n");
    
56.                 pthread_cancel(thr);
    
57.         }
    
58. 
    
59.         pthread_join(thr, &res);
    
60.         if(res == PTHREAD_CANCELED)
    
61.                 printf("Thread was canceled; cnt = %d\n", cnt);
    
62.         else
    
63.                 printf("Thread terminated normally; cnt = %d\n", cnt);
    
64.         exit(EXIT_SUCCESS);
    
65. }

#include
#include
#include
#include
void clean_fun1(void * arg)
{
printf("this is clean fun1\n");
}
void clean_fun2(void * arg)
{
printf("this is clean fun2\n");
}
void * thread_fun(void * arg)
{
pthread_cleanup_push(clean_fun1,NULL);
pthread_cleanup_push(clean_fun2,NULL);
sleep(100);
//这里要注意,如果将sleep(100);换成while(1);的话,程序会一直暂停.push和pop要成对出现.
//因为while(1);运行的太快,线程不接受cancel信号
//while(1);
pthread_cleanup_pop(0);
pthread_cleanup_pop(0);
return NULL;
}
int main()
{
pthread_t tid1;
int err;
err=pthread_create(&tid1,NULL,thread_fun,NULL);
if(err!=0)
{
perror("pthread_create");
exit(0);
}
sleep(3);
//printf("test\n");
err=pthread_cancel(tid1);
if(err!=0)
{
perror("cancel error:");
exit(0);
}
err=pthread_join(tid1,NULL);
if(err!=0)
{
perror("pthread_join  error:");
exit(0);
}

return 0;
}