#include <stdio.h>
#include <unistd.h>
#include <sys/times.h>
void my_usleep(unsigned int microseconds);
int main()
{
my_usleep(1e6);
my_usleep(1e5);
my_usleep(1e4);
my_usleep(1e3);
my_usleep(1e2);
my_usleep(1);
printf("Finished\n");
}
void my_usleep(unsigned int microseconds)
{
clock_t tick1=-1, tick2=-1;
double dClock = -1;
struct tms tStruct1, tStruct2;
if((tick1 = times(&tStruct1))== -1) printf("Error time 1\n");
usleep(microseconds);
if((tick2 = times(&tStruct2))== -1) printf("Error time 2\n");
if((dClock = sysconf(_SC_CLK_TCK)) < 0) printf("Error sysconf \n");
printf("usleep(%d) takes %6.2f ms\n", microseconds, (1000*(tick2 -
tick1)/dClock) );
return;
}

usleep(1000000) takes 1010.00 ms
usleep(100000) takes 110.00 ms
usleep(10000) takes  20.00 ms
usleep(1000) takes  20.00 ms
usleep(100) takes  20.00 ms
usleep(1) takes  20.00 ms
Finished

2 Antworten zu dieser Frage

1. Antwort von nach einem Tag 0 hilfreich

   Re: usleep takes to much time !

   Hello Lars
   
   I'm not an linux specialist but:
   
   usleep() normaly waits not for microseconds, as you may think, but it waits for systemticks !!!!
   
   The value of dClock gives you the amount of ticks per second ( the value of dClock for your system seems to be 50 equal 20 ms between to ticks). void my_usleep(unsigned int microseconds)
   {
   clock_t tick1=-1, tick2=-1;
   double dClock = -1;
   struct tms tStruct1, tStruct2;
   
   if((tick1 = times(&tStruct1))== -1) printf("Error time 1\n");
   usleep(microseconds);
   if((tick2 = times(&tStruct2))== -1) printf("Error time 2\n");
   if((dClock = sysconf(_SC_CLK_TCK)) < 0) printf("Error
   sysconf \n");
   
   printf("usleep(%d) takes %6.2f ms\n", microseconds,
   (1000*(tick2 -
   tick1)/dClock) );
   return;
   }
   
   
   I get the following output:
   

   
   
   usleep(1000000) takes 1010.00 ms
   
   usleep(100000) takes 110.00 ms
   
   usleep(10000) takes  20.00 ms
   
   usleep(1000) takes  20.00 ms
   
   usleep(100) takes  20.00 ms
   
   usleep(1) takes  20.00 ms
   
   Finished
   
   

   
   
   Please, can anybody tell me why a usleep(1 usec) takes 20 ms ?
   (Linux 2.4, glibc2.2, gcc 2.95.2)
   Peter(TOO)
   

   • Antwort von nach einem Tag 0 hilfreich

     Re^2: usleep takes to much time !

     Hi Peter,
     
     I think you are right. However, I have
     a requirement to wait for exactly x/1000 seconds. I will try to
     realize this with the realtime clock (/dev/rtc), but I'm wondering that there is no other way for this, like
     the funktion "VOID Sleep(DWORD dwMilliseconds)" in win32. This function seems to wait exactly for the specified mseconds.
     Any Idea ?
     
     Thanks for your response.
     Lars Hello Lars
     
     I'm not an linux specialist but:
     
     usleep() normaly waits not for microseconds, as you may
     think, but it waits for systemticks !!!!
     
     The value of dClock gives you the amount of ticks per second (
     the value of dClock for your system seems to be 50 equal 20 ms
     between to ticks).
     
     >....