Re: usleep

[Stephen Samuel <samuel@bcgreen.com>]

On my box, (a P3/450) usleep seems to have an overhead of about 10000usec
and a minimum response time of about 20000

/* my test prog:
  * (based on yours)
  */

#include <unistd.h>
#include <sys/time.h>

struct timeval tv1,tv2;
#define PAUSE 100000

int main()
{
     while (1)
     {
         int i;
         double sum=0.0,t;
         gettimeofday(&tv2, NULL);
         printf("hello\n");
         for(i = 0; i < 20 ; i++)
         {
                 gettimeofday(&tv1, NULL);
             usleep(PAUSE);
                gettimeofday(&tv2, NULL);
                printf("slept %9.6fs\n", t=tv2.tv_sec+tv2.tv_usec*.000001 -tv1.tv_sec-tv1.tv_usec*.000001 );
                sum+=t;
         }
         printf ("average %9.6fs\n",sum/i);
         sleep (5);
     }
}



Lee Chin wrote:
 > I would think the following code would wait for 1 second each itteration before printing hello, but it waits way too long.  Replacing the for loop body with a
 > usleep(1000000) works great... what am I missing here?
 >
 > Thanks
 > Lee



-- 
Stephen Samuel +1(604)876-0426                samuel@bcgreen.com
		   http://www.bcgreen.com/~samuel/
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