Messages in this thread | | | Date | Mon, 24 Jun 2002 15:44:02 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: gettimeofday problem |
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On Mon, 24 Jun 2002, Salvatore D'Angelo wrote:
> In this piece of code I convert seconds and microseconds in > milliseconds. I think the problem is not in my code, in fact I wrote the > following piece of code in Java, and it does not work too. In the for > loop the 90% of times b > a while for 10% of times not. > > class Prova { > public static void main(....) { > for (;;) { > long a = System.currentTimeMillis(); > long b = System.currentTimeMillis(); > > if (a > b) { > System.out.println("Wrong!!!!!!!!!!!!!"); > } > } > } > } > >
This has been running since I first read your mail about 10:00 this morning. The kernel is 2.4.18
#include <stdio.h> #include <sys/time.h> #define MICRO 1000000 #define ULL unsigned long long int main(void); static ULL tim(void);
static ULL tim() { struct timeval t; (void)gettimeofday(&t, NULL); return (ULL)t.tv_sec * MICRO + (ULL)t.tv_usec; } int main() { ULL a, b, cnt; for(cnt=0;;cnt++) { a = tim(); b = tim(); if(b < a) break; } printf("Failed after %llu\n", cnt); printf("a = %llu, b = %llu\n", a, b); return 0; }
It seems to work fine. That said, I didn't use your code or check for the possibility of a sign-change miscompare. I just made sure I don't have any by using unsigned stuff. You may want to try this code to see if you have a compiler (or coding) problem.
Cheers, Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Windows-2000/Professional isn't.
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