因爲main函數和信號處理函數中都調用getpwnam函數,而在getpwnam函數中會調用malloc和free,如果主函數malloc之後收到SIGALRM信號進入信號處理函數,在信號處理函數裏malloc然後free,而在信號處理函數調用free和main函數也在調用free時,malloc和free維護的數據結構就出現了損壞。
所以在信號處理函數中調用非可重入函數,則其結果是不可預知的。
1.源代碼:
cat -n 10_5.c
1 #include "apue.h"
2 #include <pwd.h>
3
4 static void handler(int signo)
5 {
6 struct passwd *rootptr;
7
8 if ((rootptr = getpwnam("root")) == NULL ){
9 err_sys("getpwnam(root) error");
10 }
11
12 alarm(1);
13 }
14
15 int main()
16 {
17 struct passwd *ptr;
18 signal(SIGALRM,handler);
19 alarm(1);
20
21 for (; ;){
22 if ((ptr = getpwnam("tingbinz")) == NULL)
23 err_sys("getpwnam error");
24 if (strcmp(ptr->pw_name,"tingbinz") != 0)
25 printf("return value corrupted!,pw_name = %s\n",ptr->pwname);
26 }
27 }
2.運行結果:
gcc -ggdb3 -Wall -o call_not_reload_getpwnam 10_5.c
In file included from apue.h:132,
from 10_5.c:1:
error.c: In function `err_doit':
error.c:121: warning: implicit declaration of function `vsnprintf'
error.c:123: warning: implicit declaration of function `snprintf'
./call_not_reload_getpwnam
Alarm Clock