[英]RT timer strange behavior
我正在学习如何使用 RT 计时器来创建周期性事件。 我尝试使用基于 timer_create 文档示例的示例。
预期的行为是每 5 秒产生一个周期性事件,同时主执行休眠 30 秒,但我得到以下行为。
定时器在主执行休眠时被创建和初始化。 5 秒后定时器事件产生,相应的处理程序被调用,当处理程序函数完成时,主执行被唤醒,经过的时间是 5 秒,但必须是 30 秒。
/* gcc main.c -Wall -Wextra -lrt -o timer */
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <time.h>
/* Macros *********************************************************************/
#define CLOCKID CLOCK_REALTIME
/* Real-time signals number */
#define RT_SIGNAL_NUM SIGRTMIN
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE);} while (0)
#define MAIN_SLEEP 30
#define TIMER_TIME 5
/* Global data ****************************************************************/
struct itimerspec gIts;
timer_t gTimerId;
/* Functions ******************************************************************/
static void handler(int sig, siginfo_t *si, void *uc)
{
int or;
timer_t *tidp;
/* Note: calling printf() from a signal handler is not
strictly correct, since printf() is not async-signal-safe;
see signal(7) */
printf("Caught signal %d\n", sig);
signal(sig, SIG_IGN);
}
void main(int argc, char *argv[])
{
struct sigevent sev;
long long freq_nanosecs;
sigset_t mask;
struct sigaction sa;
time_t begin, end;
double time_spent;
(void) argc;
(void) argv;
/* Establish handler for Real-time signal */
printf("Establishing handler for signal %d\n", RT_SIGNAL_NUM);
/* If SA_SIGINFO is specified in sa_flags, then sa_sigaction (instead of
* sa_handler) specifies the signal-handling function for signum.
*/
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = handler;
/* the Signal no would be masked. */
sigemptyset(&sa.sa_mask);
/* Change the action taken by a process on receipt of a specific signal. */
if (-1 == sigaction(RT_SIGNAL_NUM, &sa, NULL))
{
errExit("sigaction");
}
/* Configure timer:
* SIGEV_SIGNAL: Upon timer expiration, generate the signal sigev_signo for
* the process.
*/
sev.sigev_notify = SIGEV_SIGNAL;
sev.sigev_signo = RT_SIGNAL_NUM;
sev.sigev_value.sival_ptr = &gTimerId;
/* Create and init the timer */
if (-1 == timer_create(CLOCKID, &sev, &gTimerId))
{
errExit("timer_create");
}
printf("timer ID is 0x%lx\n", (long) gTimerId);
/* Start the timer */
gIts.it_value.tv_sec = TIMER_TIME ;
gIts.it_value.tv_nsec = 0;
gIts.it_interval.tv_sec = TIMER_TIME;
gIts.it_interval.tv_nsec = 0;
if (-1 == timer_settime(gTimerId, 0, &gIts, NULL))
{
errExit("timer_settime");
}
/* Sleep for a while; meanwhile, the timer may expire multiple times */
struct itimerspec currTime;
printf("Main Sleep for %d seconds\n", MAIN_SLEEP);
begin = time(NULL);
sleep(MAIN_SLEEP);
end = time(NULL);
printf("Main Wake up\n");
time_spent = (double)(end - begin);
timer_gettime(gTimerId, &currTime);
printf("Main sleep elapsed time = %f s %d %d\n",time_spent);
printf("Timer time = %ld s\n",currTime.it_value.tv_sec);
exit(EXIT_SUCCESS);
}
这是执行输出:
Establishing handler for signal 34
timer ID is 0x9522008
Main Sleep for 30 seconds
Caught signal 34
Main Wake up
Main sleep elapsed time = 5.000000 s
Timer time = 4 s
有人可以帮我弄清楚这里发生了什么吗?
提前致谢。
当信号产生时, sleep
功能被中断并立即返回。 引用sleep
的手册页
sleep() 函数会挂起调用线程的执行,直到 [时间已] 过去或将信号传递给线程,并且其操作是调用信号捕获函数或终止线程或进程。
幸运的是, sleep
函数的返回值是剩余的睡眠时间,因此您可以像这样在循环中简单地调用sleep
int t = 30;
while ( t > 0 )
t = sleep( t );
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