High precision time under Linux

Today in the company code to see the use of the time-out function of the Select function as the use of timers, and then organized the following several micro-level Linux timer. In my Ubutu10.10 dual-core environment, the compilation passes.

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2. /*
4. * @FileName: TEST_SLEEP.C
6. * @Author: WZJ
8. * @Brief:
10. *
12. *
14. * @History:
16. *
18. * @Date: February 07, 2012 Tuesday 22:20:00
20. *
22. */
24. #include <stdio.h>
26. #include <stdlib.h>
28. #include <time.h>
30. #include <sys/time.h>
32. #include <errno.h>
34. #include <string.h>
36. #include <unistd.h>
38. #include <sys/types.h>
40. #include <sys/select.h>
46. int main (int argc, char **argv)
48. {
50. unsigned int ntimetestsec = 0;
52. unsigned int ntimetest = 0;
54. struct Timeval tvbegin;
56. struct Timeval tvnow;
58. int ret = 0;
60. unsigned int ndelay = 0;
62. struct Timeval TV;
64. int fd = 1;
66. int i = 0;
68. struct Timespec req;
72. unsigned int delay[20] =
74. {500000, 100000, 50000, 10000, 1000, 900, 500, 100, 10, 1, 0};
76. int nreduce = 0; //Error
80. fprintf (stderr, "%19s%12s%12s%12s\n", "fuction", "Time (USEC)", "Realtime", "reduce");
82. fprintf (stderr, "----------------------------------------------------\ n");
84. For (i = 0; i <; i++)
86. {
88. if (Delay[i] <= 0)
90. Break ;
92. Ndelay = Delay[i];
94. //test Sleep
96. Gettimeofday (&tvbegin, NULL);
98. ret = Usleep (ndelay);
100. if (ret = =-1)
102. {
104. fprintf (stderr, "Usleep error, errno=%d [%s]\n", errno, Strerror (errno));
106. }
108. Gettimeofday (&tvnow, NULL);
110. Ntimetest = (tvnow.tv_sec-tvbegin.tv_sec) * 1000000 + tvnow.tv_usec-tvbegin.tv_usec;
112. Nreduce = Ntimetest-ndelay;
116. fprintf (stderr, "\ t usleep%8u%8u%8d\n", Ndelay, Ntimetest,nreduce);
120. //test Nanosleep
122. Req.tv_sec = ndelay/1000000;
124. Req.tv_nsec = (ndelay%1000000) * 1000;
128. Gettimeofday (&tvbegin, NULL);
130. ret = Nanosleep (&req, NULL);
132. if ( -1 = = ret)
134. {
136. fprintf (stderr, "\ t nanousleep%8u not support\n", ndelay);
138. }
140. Gettimeofday (&tvnow, NULL);
142. Ntimetest = (tvnow.tv_sec-tvbegin.tv_sec) * 1000000 + tvnow.tv_usec-tvbegin.tv_usec;
144. Nreduce = Ntimetest-ndelay;
146. fprintf (stderr, "\ t nanosleep%8u%8u%8d\n", Ndelay, Ntimetest,nreduce);
150. //test Select
152. tv.tv_sec = 0;
154. Tv.tv_usec = Ndelay;
158. Gettimeofday (&tvbegin, NULL);
160. ret = SELECT (0, NULL, NULL, NULL, &TV);
162. if ( -1 = = ret)
164. {
166. fprintf (stderr, "select Error.  errno =%d [%s]\n], errno, strerror (errno));
168. }
172. Gettimeofday (&tvnow, NULL);
174. Ntimetest = (tvnow.tv_sec-tvbegin.tv_sec) * 1000000 + tvnow.tv_usec-tvbegin.tv_usec;
176. Nreduce = Ntimetest-ndelay;
178. fprintf (stderr, "\ t select%8u%8u%8d\n", Ndelay, Ntimetest,nreduce);
182. //pselcet
184. Req.tv_sec = ndelay/1000000;
186. Req.tv_nsec = (ndelay%1000000) * 1000;
190. Gettimeofday (&tvbegin, NULL);
192. ret = pselect (0, NULL, NULL, NULL, &REQ, NULL);
194. if ( -1 = = ret)
196. {
198. fprintf (stderr, "select Error.  errno =%d [%s]\n], errno, strerror (errno));
200. }
204. Gettimeofday (&tvnow, NULL);
206. Ntimetest = (tvnow.tv_sec-tvbegin.tv_sec) * 1000000 + tvnow.tv_usec-tvbegin.tv_usec;
208. Nreduce = Ntimetest-ndelay;
210. fprintf (stderr, "\ t pselect%8u%8u%8d\n", Ndelay, Ntimetest,nreduce);
214. fprintf (stderr, "--------------------------------\ n");
218. }
222. return 0;
224. }

The boss suggested that we use Select () as a timer in the case of high precision requirements, the greatest benefit is that it will not affect signal processing, thread safety, and accuracy can be guaranteed. In this experiment, when the time delay time is longer, select and Pselect performance is poor, when the time is less than 1 milliseconds, their accuracy is improved, performance is comparable with Usleep, nanosleep, sometimes even more accurate than the latter

High precision time under Linux