DB<25>  use Time::HiRes qw( time sleep );

  DB<26>  print time, "\n";$nextsecond = int time + 1;sleep $nextsecon
+d - time;print time, "\n"
1579981231.91855
1579981232.00031

  DB<27>
[download]

Which is normally not a problem, if the loops body starts with the sleep, before doing something.

Thanks for the lightbulb. I see no error since doing it that way. I wonder if the perldoc for sleep should add something like:

To delay ON each second, don't sleep FOR one second, sleep until the NEXT second, using sleep and time from Time::HiRes:

Explain why this is a subtle trap:

while () {
  print something();
  sleep 1 # WRONG!
}

Calculate the next second:

use Time::HiRes qw/sleep time/;
while () {
  print something();
  sleep do { (int time + 1) - time } # RIGHT!
}

You are missing the conceptual loophole here.

> print something();

So what if something() takes longer than a second?

Your sleep would just skip the missed steps till the following interval.

The clean approach would be to include an exception handling.

Apart from this could the OS be too busy to return in time, that's why sleep only guaranties minimal time.

See Re: missing second of time

> I wonder if the perldoc for sleep should add ...

All these conditions might not be true in your case, but how do you want to include the general case in the docs???

I think this use cases are best covered in a dedicated module.

Update

Might be interesting to compare how setInterval() in JS is handling those cases.

Update

From what I read after searching JS setInterval long running function it seems that delayed calls are queued to be executed later, and this without raising an exception. ... Ugly.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

Time::HiRes::sleep(-0.202505): negative time not invented yet

I tried the second solution with the fudge factor but it goes negative in less than an hour. I'll go back to the original suggestion and make sure the value is not negative before using it to sleep. Thanks again

Try this one

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11111868
use warnings;
use Time::HiRes qw( time sleep );

my $fudgefactor = 0.001;
while(1)
  {
  my $time = time;
  my $nextsecond = int $time + 1;
  my $interval =  $nextsecond - $time - $fudgefactor;
  $interval > 0 and sleep $interval;
  1 while time < $nextsecond;
  printf "%.6f\n", time;
  }
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