写一个Linux系统下的定时器demo

以下是一个简单的Linux系统下的定时器demo，使用了C语言和POSIX定时器API：

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>

void timer_handler(int signum)
{
    printf("Timer expired.\n");
}

int main()
{
    timer_t timerid;
    struct sigevent sigev;
    struct itimerspec timer_spec;

    // 创建定时器信号处理函数
    sigev.sigev_notify = SIGEV_SIGNAL;
    sigev.sigev_signo = SIGUSR1;
    sigev.sigev_value.sival_ptr = &timerid;
    if (timer_create(CLOCK_REALTIME, &sigev, &timerid) == -1) {
        perror("timer_create");
        exit(EXIT_FAILURE);
    }

    // 设置定时器时间
    timer_spec.it_value.tv_sec = 5;
    timer_spec.it_value.tv_nsec = 0;
    timer_spec.it_interval.tv_sec = 0;
    timer_spec.it_interval.tv_nsec = 0;
    if (timer_settime(timerid, 0, &timer_spec, NULL) == -1) {
        perror("timer_settime");
        exit(EXIT_FAILURE);
    }

    // 设置定时器信号处理函数
    struct sigaction sa;
    sa.sa_handler = timer_handler;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    if (sigaction(SIGUSR1, &sa, NULL) == -1) {
        perror("sigaction");
        exit(EXIT_FAILURE);
    }

    // 等待定时器信号
    printf("Waiting for timer expiration...\n");
    pause();

    return 0;
}

此程序创建了一个定时器，设置了定时器时间为5秒，并且设置了一个定时器信号处理函数，当定时器时间到时，会触发SIGUSR1信号，从而执行定时器信号处理函数。程序会等待定时器信号的到来，直到定时器时间到达。