PR kern/14034: gettimeofday() returns negative value?

[Sabrina Minshall]

What's going one here? Successive calls to gettimeofday 
yields negative elapsed time?

Any fixes?

~~~~negtime.c~~~~

#include <sys/param.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/select.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <unistd.h>

int
time_elapsed(struct timeval *t1, struct timeval *t2)
{
        int s, ms;

        s = t1->tv_sec - t2->tv_sec;
        assert((s >= 0));
        if (s != 0) { 
                if (t1->tv_usec < t2->tv_usec) {
                        s--;
                        t1->tv_usec += 1000000;
                }
        } 
        ms = s * 1000000 + (t1->tv_usec - t2->tv_usec);
        return (ms);
}

int 
main()
{
        struct timeval tv1, tv2;
        int diff;

        if (gettimeofday(&tv1, NULL) < 0) {
                perror("gettimeofday");
        }
        tv2 = tv1;

        for (;;) {
                usleep(2000);
                if (gettimeofday(&tv1, NULL) < 0) {
                        perror("gettimeofday");
                }

                /*
                 * diff in usec.
                 */
                diff = time_elapsed(&tv1, &tv2);
                if (diff < 0) {

                        printf("-ve tvdiff %d\n", diff);
                        printf("%ld %ld %ld %ld\n",
                                        tv1.tv_sec, tv1.tv_usec,
                                        tv2.tv_sec, tv2.tv_usec);
                        assert(0);
                }
                tv2 = tv1;
        }
        return (0);
}


~~~~negtime.c~~~~

hacker ~>./a.out 
-ve tvdiff -979993
948332324 35044 948332324 1015037
assertion "0" failed: file "negtime.c", line 56
Abort



Thanks,


sabrina


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