.sleep()

.alarm()

.usleep()

.nanosleep()

.clock_nanosleep()

.getitimer()/setitimer()

.timer_create()/timer_settime/timer_gettime()/timer_delete()

.timerfd_create()/timerfd_gettime()/timer_settime()

int timer_create(int clockid,int flags);

//成功返回0

int timerfd_settime(int fd,int flags

const struct itimerspec *new_value

struct itimerspec *old_value);

//成功返回0

struct itimerspec {

struct timespec it_interval; /* Interval for periodic timer */

struct timespec it_value; /* Initial expiration */

};

struct timespec {

time_t tv_sec; /* Seconds */

long tv_nsec; /* Nanoseconds */

};

#include <sys/timerfd.h>

#include <time.h>

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <stdint.h> /* Definition of uint64_t */

#define handle_error(msg) \

do { perror(msg); exit(EXIT_FAILURE); } while (0)

//打印當前定時距首次開始計時的時間

static void print_elapsed_time(void)

{

static struct timespec start;

struct timespec curr;

static int first_call = 1;

int secs, nsecs;

if (first_call) { //獲取開始時間

first_call = 0;

if (clock_gettime(CLOCK_MONOTONIC, &start) == -1)

handle_error("clock_gettime");

}

if (clock_gettime(CLOCK_MONOTONIC, &curr) == -1)

handle_error("clock_gettime");

//時間差等于每次的當前時間減去start的開始時間

secs = curr.tv_sec - start.tv_sec;

nsecs = curr.tv_nsec - start.tv_nsec;

if (nsecs < 0) {

secs--;

nsecs += 1000000000; //相差的納秒數

}

printf("%d.%03d: ", secs, (nsecs + 500000) / 1000000);

}

int main(int argc, char *argv[])

{

struct itimerspec new_value;

int max_exp, fd;

struct timespec now;

uint64_t exp, tot_exp;

ssize_t s;

if ((argc != 2) && (argc != 4)) {

fprintf(stderr, "%s init-secs [interval-secs max-exp]\n",

argv[0]);

exit(EXIT_FAILURE);

}

if (clock_gettime(CLOCK_REALTIME, &now) == -1)

handle_error("clock_gettime");

/* Create a CLOCK_REALTIME absolute timer with initial

expiration and interval as specified in command line */

new_value.it_value.tv_sec = now.tv_sec + atoi(argv[1]);

new_value.it_value.tv_nsec = now.tv_nsec;

if (argc == 2) {

new_value.it_interval.tv_sec = 0;

max_exp = 1;

} else {

new_value.it_interval.tv_sec = atoi(argv[2]); //之后的定時間隔

max_exp = atoi(argv[3]); //定時總次數

}

new_value.it_interval.tv_nsec = 0;

//生成與定時器關聯的文件描述符

fd = timerfd_create(CLOCK_REALTIME, 0);

if (fd == -1)

handle_error("timerfd_create");

if (timerfd_settime(fd, TFD_TIMER_ABSTIME, &new_value, NULL) == -1)

handle_error("timerfd_settime");

//獲取并打印首次首次定時開始的時間

print_elapsed_time();

printf("timer started\n");

for (tot_exp = 0; tot_exp < max_exp;) {

s = read(fd, &exp, sizeof(uint64_t)); //read阻塞等待知道超時發生

if (s != sizeof(uint64_t))

handle_error("read");

tot_exp += exp;

print_elapsed_time();

printf("read: %llu; total=%llu\n",

(unsigned long long) exp,

(unsigned long long) tot_exp);

}

exit(EXIT_SUCCESS);

}