第 23 章 定时器与休眠 (Timers and Sleeping)

#include <sys/time.h>

struct itimerval {
    struct timeval it_interval;     /* 重复间隔 */
    struct timeval it_value;        /* 首次到期 */
};

int setitimer(int which, const struct itimerval *new_value, struct itimerval *old_value);
int getitimer(int which, struct itimerval *curr_value);

// 摘自《The Linux Programming Interface》第 23 章（Listing 23-1 简化）
struct itimerval itv;
itv.it_value.tv_sec = 1; itv.it_value.tv_usec = 800000;
itv.it_interval.tv_sec = 1; itv.it_interval.tv_usec = 0;
setitimer(ITIMER_REAL, &itv, NULL);
/* SIGALRM handler 设 gotAlarm = 1；主循环检查 gotAlarm */

/* 1. 设 SIGALRM handler（不 SA_RESTART） */
struct sigaction sa = {0};
sa.sa_handler = sigalrm_handler;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;                        /* 不自动重启 */
sigaction(SIGALRM, &sa, NULL);

/* 2. 设 timer */
alarm(seconds);                         /* 或 setitimer */

/* 3. 阻塞系统调用 */
n = read(fd, buf, sizeof(buf));

/* 4. 禁用 timer（如果调用提前返回） */
alarm(0);

/* 5. 检查 EINTR */
if (n == -1 && errno == EINTR) { /* 超时 */ }
else { /* 正常 */ }

#include <time.h>
int nanosleep(const struct timespec *req, struct timespec *rem);
int clock_nanosleep(clockid_t clockid, int flags,
                    const struct timespec *request,
                    struct timespec *remain);

struct timespec start, end;
clock_gettime(CLOCK_MONOTONIC, &start);
do_work();
clock_gettime(CLOCK_MONOTONIC, &end);
double elapsed = (end.tv_sec - start.tv_sec) +
                 (end.tv_nsec - start.tv_nsec) / 1e9;

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

timer_t timerid;
struct sigevent sev = {
    .sigev_notify = SIGEV_SIGNAL,           /* 投递信号 */
    .sigev_signo = SIGUSR1,                 /* 或 SIGRTMIN+x */
    .sigev_value.sival_ptr = &timerid       /* sigval 携带数据 */
};
timer_create(CLOCK_MONOTONIC, &sev, &timerid);

struct itimerspec its = {
    .it_value = { .tv_sec = 5, .tv_nsec = 0 },     /* 首次到期 5 秒 */
    .it_interval = { .tv_sec = 1, .tv_nsec = 0 }   /* 之后每秒 */
};
timer_settime(timerid, 0, &its, NULL);

timer_delete(timerid);

#include <sys/timerfd.h>

int tfd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC);

struct itimerspec its = {
    .it_value = { .tv_sec = 5, .tv_nsec = 0 },
    .it_interval = { .tv_sec = 1, .tv_nsec = 0 }
};
timerfd_settime(tfd, 0, &its, NULL);

/* tfd 加入 epoll */
struct epoll_event ev = { .events = EPOLLIN, .data.fd = tfd };
epoll_ctl(epfd, EPOLL_CTL_ADD, tfd, &ev);

/* 事件循环 */
while (1) {
    int n = epoll_wait(epfd, events, MAX, -1);
    for (i = 0; i < n; i++) {
        if (events[i].data.fd == tfd) {
            uint64_t cnt;
            read(tfd, &cnt, sizeof(cnt));
            /* cnt 是到期次数 */
        }
    }
}