Linux下的微秒级定时器: usleep, nanosleep, select, pselect
16lz
2021-01-22
今天在公司代码中看到了使用select函数的超时功能作定时器的用法，便整理了如下几个Linux下的微秒级别的定时器。在我的Ubutu10.10 双核环境中，编译通过。
/*
* @FileName: test_sleep.c
* @Author: wzj
* @Brief:
*
*
* @History:
*
* @Date: 2012年02月07日星期二22:20:00
*
*/
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<sys/time.h>
#include<errno.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/select.h>
int main(int argc, char **argv)
{
unsigned int nTimeTestSec = 0;
unsigned int nTimeTest = 0;
struct timeval tvBegin;
struct timeval tvNow;
int ret = 0;
unsigned int nDelay = 0;
struct timeval tv;
int fd = 1;
int i = 0;
struct timespec req;
unsigned int delay[20] =
{500000, 100000, 50000, 10000, 1000, 900, 500, 100, 10, 1, 0};
int nReduce = 0; //误差
fprintf(stderr, "%19s%12s%12s%12s\n", "fuction", "time(usec)", "realtime", "reduce");
fprintf(stderr, "----------------------------------------------------\n");
for (i = 0; i < 20; i++)
{
if (delay[i] <= 0)
break;
nDelay = delay[i];
//test sleep
gettimeofday(&tvBegin, NULL);
ret = usleep(nDelay);
if(ret == -1)
{
fprintf(stderr, "usleep error, errno=%d [%s]\n", errno, strerror(errno));
}
gettimeofday(&tvNow, NULL);
nTimeTest = (tvNow.tv_sec - tvBegin.tv_sec) * 1000000 + tvNow.tv_usec - tvBegin.tv_usec;
nReduce = nTimeTest - nDelay;
fprintf (stderr, "\t usleep %8u %8u %8d\n", nDelay, nTimeTest,nReduce);
//test nanosleep
req.tv_sec = nDelay/1000000;
req.tv_nsec = (nDelay%1000000) * 1000;
gettimeofday(&tvBegin, NULL);
ret = nanosleep(&req, NULL);
if (-1 == ret)
{
fprintf (stderr, "\t nanousleep %8unot support\n", nDelay);
}
gettimeofday(&tvNow, NULL);
nTimeTest = (tvNow.tv_sec - tvBegin.tv_sec) * 1000000 + tvNow.tv_usec - tvBegin.tv_usec;
nReduce = nTimeTest - nDelay;
fprintf (stderr, "\t nanosleep %8u %8u %8d\n", nDelay, nTimeTest,nReduce);
//test select
tv.tv_sec = 0;
tv.tv_usec = nDelay;
gettimeofday(&tvBegin, NULL);
ret = select(0, NULL, NULL, NULL, &tv);
if (-1 == ret)
{
fprintf(stderr, "select error. errno = %d [%s]\n", errno, strerror(errno));
}
gettimeofday(&tvNow, NULL);
nTimeTest = (tvNow.tv_sec - tvBegin.tv_sec) * 1000000 + tvNow.tv_usec - tvBegin.tv_usec;
nReduce = nTimeTest - nDelay;
fprintf (stderr, "\t select %8u %8u %8d\n", nDelay, nTimeTest,nReduce);
//pselcet
req.tv_sec = nDelay/1000000;
req.tv_nsec = (nDelay%1000000) * 1000;
gettimeofday(&tvBegin, NULL);
ret = pselect(0, NULL, NULL, NULL, &req, NULL);
if (-1 == ret)
{
fprintf(stderr, "select error. errno = %d [%s]\n", errno, strerror(errno));
}
gettimeofday(&tvNow, NULL);
nTimeTest = (tvNow.tv_sec - tvBegin.tv_sec) * 1000000 + tvNow.tv_usec - tvBegin.tv_usec;
nReduce = nTimeTest - nDelay;
fprintf (stderr, "\t pselect %8u %8u %8d\n", nDelay, nTimeTest,nReduce);
fprintf (stderr, "--------------------------------\n");
}
return 0;
}
老大建议我们在对精度要求较高的情况下使用select()作为定时器，最大的好处就是不会影响信号处理，线程安全，而且精度能得到保证。在这个实验中，当时间延时时间较长时，select和pselect表现较差，当时间小于1毫秒时，他们的精确度便提高了，表现与usleep、nanosleep不相上下，有时精度甚至超过后者。