This can be done without a busy loop. 

use Time::HiRes qw( time sleep );

use constant {
   TIMES_PER_PERIOD => 3,    # Integer
   PERIOD           => 1.0,  # Fractional seconds
};

my @times = (0) x TIMES_PER_PERIOD;
while (my $r = get_request()) {
   my $wait = ($times[0] + PERIOD) - time();
   if ($wait > 0) {
      sleep($wait);
      redo;  # In case sleep got interrupted.
   }

   do_request($r);
   shift(@times);
   push(@times, time());
}

[download]

(My placement of do_request prevents more than three request from being served per second. Move do_request after the push to prevent more than three requests from being started per second. roboticus and JavaFan used the latter interpretation.)

It's not that useful here. Since the requests are coming from a file, they are coming in as fast as they can be serviced, so waiting is going to be necessary.

In reply to Re^2: do something no more than 3 times a second by ikegami
in thread do something no more than 3 times a second by Anonymous Monk

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