您好,我正在研究这段代码:
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdbool.h>
volatile sig_atomic_t print_flag = true;
static int count = 0;
void timer_handler (int signum)
{
printf ("timer expired %d times\n", ++count);
if(count>20) {
print_flag = false;
}
}
int main ()
{
struct sigaction sa;
struct itimerval timer;
/* Install timer_handler as the signal handler for SIGVTALRM. */
memset (&sa, 0, sizeof (sa));
sa.sa_handler = &timer_handler;
sigaction (SIGALRM, &sa, NULL);
/* Configure the timer to expire after 250 msec... */
timer.it_value.tv_sec = 0;
timer.it_value.tv_usec = 250000;
/* ... and every 250 msec after that. */
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_usec = 250000;
/* Start a virtual timer. It counts down whenever this process is
executing. */
setitimer (ITIMER_REAL, &timer, NULL);
/* Do busy work. */
while (print_flag) {
sleep(1);
}
printf("job done bye bye\n");
exit(0);
}
使用此设置一切正常,我得到此输出
...
timer expired 17 times
timer expired 18 times
timer expired 19 times
timer expired 20 times
timer expired 21 times
job done bye bye
如果我尝试更改代码评论timer.it_interval.tv_usec
和timer.it_interval.tv_usec
并将timer.it_value.tv_sec
和timer.it_value.tv_sec
设置为等于,例如3,那么它不会做他的工作。
但是,如果我像这样保持tv_usec
的明确声明,那就可以了:
timer.it_value.tv_sec = 3;
timer.it_value.tv_usec = 0;
timer.it_interval.tv_sec = 3;
timer.it_interval.tv_usec = 0;
为什么我在两个字段的tv_usec
明确声明上绑定了?
答案 0 :(得分:2)
如果您未初始化*.tv_usec
字段,则其值未定义。如果它包含的值大于999999
或小于0
,则setitimer ()
将失败并显示EINVAL
,如手册页中所述。
您应该自己初始化所有数据。如果您愿意保存一行代码,则可以memset
timer
结构0
sa
{{1}} {{1}}。{/ 1}}。