Re: strange message before sending mail

Reed Underwood wrote in
 <[email protected]>:
 |On 8/19/26 10:51, Ian Collier via Mutt-dev wrote:
 |> On Wed, Aug 19, 2026 at 01:43:57PM +0200, Vincent Lefevre wrote:
 |>> This is fine. However, I can reproduce the issue many times
 |>> every second with
 |> [redacted]
 |>
 |> That's bizarre.  So it seems the output of time(2) is delayed by
 |> at least one jiffy with respect to the real time.  Vide:
 |>
 |>
 |> #include <stdio.h>
 |> #include <time.h>
 |> #include <sys/time.h>
 |>
 |> int main(void) {
 |>    struct timeval tv;
 |>    time_t t;
 |>    while (1) {
 |>      gettimeofday(&tv, NULL);
 |>      t = time(NULL);
 |>      if (t < tv.tv_sec)
 |>        printf("%ld < %ld.%06d\n", (long)t, (long)tv.tv_sec, (int)tv.tv_us\
 |>        ec);
 |>}
 |>}
 |>
 |>
 |> This produces output on every system I've tested so far, from Centos7
 |> (3.10.0) upwards.  But the generic 6.8.0 kernel on Ubuntu 24.04 (and
 |> all earlier systems) does not produce output for the test that touches a
 |> file.  Whereas Ubuntu 24.04 systems running an OEM kernel (6.17.0) and
 |> all Fedora systems do produce output from both tests.
 |>
 |> This seems to mean that the Linux kernel has changed something about
 |> how the time is obtained when touching a file; but ultimately it is
 |> the time(2) call that is to blame.
 |>
 |> Ian Collier.
 |I can confirm the behavior you describe in Ubuntu 24.04 (6.8.0 kernel).
 |
 |For what it's worth, the behavior is not reproducible in FreeBSD.

Maybe it is because of some strange vdso(7) effect.
And i cannot reproduce it on the Musl C library based AlpineLinux.

  #include <stdio.h>
  #include <time.h>
  #include <sys/time.h>
  int main(void){
    struct timeval tv;
    time_t t;
    unsigned y, n;
    for(y = n = 0; y < 10;){
      gettimeofday(&tv, NULL);
      t = time(NULL);
      if(t < tv.tv_sec)
        ++y;
      else
        ++n;
    }
    printf("%u EQ, %u non-EQ\n", n, y);
    return 0;
  }

results in

  #?1300.00 1/120|sdaoden:tmp$ timeout 10 ./zt
  Terminated
  #?1430.00 1/120|sdaoden:tmp$ timeout 10 ./zt
  Terminated                 timeout 10 ./zt

whereas on GNU based C library (both kernel 6.18), trimmed

  #?0|lecce:tmp$ time ./zt
  52512820 EQ, 10 non-EQ
  real    0m0.915s
  #?0|lecce:tmp$ time ./zt
  6650069 EQ, 10 non-EQ
  real    0m0.124s
  #?0|lecce:tmp$ time ./zt
  6192365 EQ, 10 non-EQ
  real    0m0.118s
  #?0|lecce:tmp$ time ./zt
  14050552 EQ, 10 non-EQ
  real    0m0.345s
  #?0|lecce:tmp$ time ./zt
  15367605 EQ, 10 non-EQ
  real    0m0.377s

Musl impl is

  #?0|lecce:musl.git$ git show master:src/time/time.c
  #include <time.h>
  #include "syscall.h"

  time_t time(time_t *t)
  {
          struct timespec ts;
          __clock_gettime(CLOCK_REALTIME, &ts);
          if (t) *t = ts.tv_sec;
          return ts.tv_sec;
  }

I have not really looked into GNU C library since ~Y2K, and will
not visit that jungle.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)