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 %8u not 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