参考：https://blog.csdn.net/lengzijian/article/details/9092367 1.sleep的精度是秒 2.usleep的精度是微妙，不精确 3.select的精度是微妙，精确 struct timeval delay; delay.tv_sec = 0; delay.tv_usec = 20 * 1000; // 20 ms select(0, NULL, NULL, NULL, &delay); 4.nanosleep的精度是纳秒，不精确 unix、linux系统尽量不要使用usleep和sleep而应该使用nanosleep，使用nanosleep应注意判断返回值和错误代码，否则容易造成cpu占用率100%。
/* make: gcc -o test_sleep test_sleep.c */ #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> #define PRINT_USEAGE { \ fprintf(stderr,"\n Usage: %s usec ",argv[0]); \ fprintf(stderr,"\n\n");\ } int main (int argc, char **argv) { unsigned int nTimeTestSec = 0; /* sec */ unsigned int nTimeTest = 0; /* usec */ struct timeval tvBegin; struct timeval tvNow; int ret = 0; unsigned int nDelay = 0; /* usec */ fd_set rfds; 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 */ #if 0 if (argc < 2) { PRINT_USEAGE; exit (1); } nDelay = atoi (argv[1]); #endif fprintf (stderr, "%18s%12s%12s%12s\n", "function", "time(usec)", "realTime", "reduce"); fprintf (stderr, "-------------------------------------------------------------------\n"); for (i = 0; i < 11; i++) { if (delay[i] < 0) break; nDelay = delay[i]; /* test usleep */ gettimeofday (&tvBegin, NULL); ret = usleep (nDelay); if (-1 == ret) { 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 */ gettimeofday (&tvBegin, NULL); req.tv_sec = nDelay / 1000000; req.tv_nsec = (nDelay % 1000000) * 1000; ret = nanosleep (&req, NULL); if (-1 == ret) { fprintf (stderr, "/t nanosleep %8u not support\n", nDelay); } else { 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 */ gettimeofday (&tvBegin, NULL); FD_ZERO (&rfds); FD_SET (fd, &rfds); tv.tv_sec = 0; tv.tv_usec = nDelay; 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); } return 0; }
