#include <unistd.h>
#include <stdio.h>
#include  <stdlib.h>


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

	unsigned int  timeleft;
	printf("Set the alarm and sleep\n"); 
	//设置定时器，时钟一到就发送一个信号SIGALRM到进程。
	alarm(10);
	sleep(5);
	timeleft = alarm(0); //获得上一个闹钟的剩余时间：5秒 
	printf( "Time left    before cancel, and rearm: %d\n", timeleft );
	
	alarm(timeleft);	
	printf("Hanging around, waiting to die\n"); 
	pause(); //让进程暂停直到信号出现

	return EXIT_SUCCESS;

}

#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int isExit = 1;

//通过调用alarm来设置计时器，然后继续做别的事情。当计时器计时到0时，信号发送，处理函数被调用。
static void timer(int sig) {
	
	static int count = 0;
	count++;
	printf("\ncount = %d\n", count);

	if (sig == SIGALRM)
	{
		printf("timer\n");
	} 
	signal(SIGALRM, timer); //重新注册定时器
	alarm(1);//定时1s
	if (count == 5) 
	{
		alarm(0);
		isExit = 0;		
	}	
	return;
}

//linux定时器的实现
int main(int argc, char *argv[]) {
	
	signal(SIGALRM, timer);//执行定时器函数
	printf("wait 1s\n");
	alarm(1); //定时1s	
	while (isExit)
	{
		
	};
	printf("finish\n");
	return 0;

}