一个setitimer问题(linux programming by exmaple)

wangsdu

看了linux programming by examples的第14章，课后习题有个问题想请教一下.
下面是程序
/* ch14-timers.c ---- demonstrate interval timers */

#include <stdio.h>
#include <assert.h>
#include <signal.h>
#include <sys/time.h>

/* handler --- handle SIGALRM */

void handler(int signo)
{
        static const char msg[] = "\n*** Timer expired, you lose ***\n";

        assert(signo == SIGALRM);

        write(2, msg, sizeof(msg) - 1);
        exit(1);
}

/* main --- set up timer, read data with timeout */

int main(void)
{
        struct itimerval tval;
        char string[BUFSIZ];

        timerclear(& tval.it_interval);        /* zero interval means no reset of timer */
        timerclear(& tval.it_value);

        tval.it_value.tv_sec = 10;        /* 10 second timeout */

        (void) signal(SIGALRM, handler);

        printf("You have ten seconds to enter\nyour name, rank, and serial number: ");

        (void) setitimer(ITIMER_REAL, & tval, NULL);
        if (fgets(string, sizeof string, stdin) != NULL) {
                (void) setitimer(ITIMER_REAL, NULL, NULL);        /* turn off timer */
                /* process rest of data, diagnostic print for illustration */
                printf("I'm glad you are being cooperative.\n");
        } else
                printf("\nEOF, eh?  We won't give up so easily!\n");

        exit(0);
}
问题是：
    if (fgets(string, sizeof string, stdin) != NULL) {
(void) setitimer(ITIMER_REAL, NULL, NULL); /* turn off timer */
printf("I'm glad you are being cooperative. \n");
}
else
printf("\nEOF, eh? We won't give up so easily!\n");

上面的setitimer有race condition，假设用户输入在规定时间内输入了字符，如果这时程序被suspend，那么定时器将不能被关闭，因而产生了race condition，我的问题是该怎么做呢？来尽量消除这个race condition???

wangsdu

怎么没人回答啊？？？？难道是太难了？？？

wangsdu

1. /* ch14-timers.c ---- demonstrate interval timers */
   
2. 
   
3. #include <stdio.h>
   
4. #include <assert.h>
   
5. #include <signal.h>
   
6. #include <sys/time.h>
   
7. 
   
8. /* handler --- handle SIGALRM */
   
9. 
   
10. void handler(int signo)
    
11. {
    
12.         static const char msg[] = "\n*** Timer expired, you lose ***\n";
    
13. 
    
14.         assert(signo == SIGALRM);
    
15. 
    
16.         write(2, msg, sizeof(msg) - 1);
    
17.         exit(1);
    
18. }
    
19. 
    
20. /* main --- set up timer, read data with timeout */
    
21. 
    
22. int main(void)
    
23. {
    
24.         struct itimerval tval;
    
25.         char string[BUFSIZ];
    
26. 
    
27.         timerclear(& tval.it_interval);        /* zero interval means no reset of timer */
    
28.         timerclear(& tval.it_value);
    
29. 
    
30.         tval.it_value.tv_sec = 10;        /* 10 second timeout */
    
31. 
    
32.         (void) signal(SIGALRM, handler);
    
33. 
    
34.         printf("You have ten seconds to enter\nyour name, rank, and serial number: ");
    
35. 
    
36.         (void) setitimer(ITIMER_REAL, & tval, NULL);
    
37.         if (fgets(string, sizeof string, stdin) != NULL) {
    
38.                 (void) setitimer(ITIMER_REAL, NULL, NULL);        /* turn off timer */
    
39.                 /* process rest of data, diagnostic print for illustration */
    
40.                 printf("I'm glad you are being cooperative.\n");
    
41.         } else
    
42.                 printf("\nEOF, eh?  We won't give up so easily!\n");
    
43. 
    
44.         exit(0);
    
45. }
    

复制代码