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缘由：

学习需要

正文：

参考解答：

alarm()+signal()/sigaction()实现的不那么精确的定时器功能

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h> /* struct timeval */
#include <time.h> /* time() */
#include <errno.h>

#include <inttypes.h>
#include <math.h>
void print_current_time_with_ms(void)
{
    long            ms; // Milliseconds
    time_t          s;  // Seconds
    struct timespec spec;
    clock_gettime(CLOCK_REALTIME, &spec);

    s  = spec.tv_sec;
    ms = round(spec.tv_nsec / 1.0e6); // Convert nanoseconds to milliseconds

    printf("Current time: %"PRIdMAX".%03ld seconds since the Epoch\n", (intmax_t)s, ms);
}

void sigalrm_fn(int sig)
{
	print_current_time_with_ms();
	alarm(2);	// every 2 seconds
	return;
}

int main(void)
{
	signal(SIGALRM, sigalrm_fn);
	alarm(1);	// first call ?
	while(1)
		pause();
	return 0;
}
/* $ ./a.out
Current time: 1501747559.026 seconds since the Epoch
Current time: 1501747561.026 seconds since the Epoch
Current time: 1501747563.028 seconds since the Epoch
Current time: 1501747565.032 seconds since the Epoch
Current time: 1501747567.035 seconds since the Epoch
*/

setitimer()+sigaction()的一个实现

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>

int limit = 10;

/* signal process */
void timeout_info(int signo)
{
    if(limit == 0)
    {
        printf("Sorry, time limit reached.\n");
        return;
    }
    printf("Only %d seconds left.\n", limit--);
}

/* init sigaction */
void init_sigaction(void)
{
    struct sigaction act;

    act.sa_handler = timeout_info;
    act.sa_flags   = 0;
    sigemptyset(&act.sa_mask);
    sigaction(SIGPROF, &act, NULL);
}

/* init */
void init_time(void)
{
    struct itimerval val;

    val.it_value.tv_sec = 1;
    val.it_value.tv_usec = 0;
    val.it_interval = val.it_value;
    setitimer(ITIMER_PROF, &val, NULL);
}

int main(void)
{
    init_sigaction();
    init_time();
    printf("You have only 10 seconds for thinking.\n");

    while(1);
    return 0;
}

多个setitimer()的示例

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <sys/time.h>

#include <inttypes.h>
#include <math.h>
void print_current_time_with_ms(void)
{
    long            ms; // Milliseconds
    time_t          s;  // Seconds
    struct timespec spec;
    clock_gettime(CLOCK_REALTIME, &spec);

    s  = spec.tv_sec;
    ms = round(spec.tv_nsec / 1.0e6); // Convert nanoseconds to milliseconds

    printf("Current time: %"PRIdMAX".%03ld seconds since the Epoch\n", (intmax_t)s, ms);
}

int sec = 5;

void sigroutine(int signo){
	switch (signo) {
		case SIGALRM:
			printf("Catch a signal -- SIGALRM\n");
			print_current_time_with_ms();
			signal(SIGALRM, sigroutine);
			break;
		case SIGVTALRM:
			printf("Catch a signal -- SIGVTALRM\n");
			print_current_time_with_ms();
			signal(SIGVTALRM, sigroutine);
			break;
	}
	return;
}

int main() {
	printf("process id is %d\n", getpid());

	signal(SIGALRM, sigroutine);
	signal(SIGVTALRM, sigroutine);

	struct itimerval value, ovalue, value2; //(1)

	value.it_value.tv_sec = 1;
	value.it_value.tv_usec = 0;
	value.it_interval.tv_sec = 1;
	value.it_interval.tv_usec = 0;
	setitimer(ITIMER_REAL, &value, &ovalue); //(2)

	value2.it_value.tv_sec = 0;
	value2.it_value.tv_usec = 500000;
	value2.it_interval.tv_sec = 0;
	value2.it_interval.tv_usec = 500000;
	setitimer(ITIMER_VIRTUAL, &value2, &ovalue);
	
	for(;;)
		;
	return 0;
}

参考链接：

Linux定时器的使用
http://www.cppblog.com/jerryma/archive/2012/01/31/164704.html

linux下使用select实现精确定时器
http://www.cnblogs.com/jjdiaries/p/3404380.html

Linux下定时器的使用
http://www.jyguagua.com/?p=1700

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