in reply to Re: do something no more than 3 times a second
in thread do something no more than 3 times a second

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());
}

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(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.

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Re^3: do something no more than 3 times a second
by rovf (Priest) on Nov 29, 2010 at 07:50 UTC
    This can be done without a busy loop.
    Of course, it can, if you use a HiRes timer. I've suggested the busy loop as an alternative (since the timer was already suggested by JavaFan anyway), in case the OP doesn't want to use the timer. Though doing a busy loop is quite often a bad idea, there *are* cases where it makes more sense than using this kind of timer. I thought that if the OP sees these alternatives, s/he can choose what works best in the current situation.

    -- 
    Ronald Fischer <ynnor@mm.st>
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      If you want a busy loop, just comment out the sleep line. I don't see how that makes any sense, though.

      Of course, it can, if you use a HiRes timer.

      You have to use a timer either way. Or is hires somehow meaningful in that sentence? I don't see why, so could you give a example reason?

      there *are* cases where it makes more sense

      What would be such a case? I can't think of an example where doing a busy loop is acceptable if the system has a notification API. (In this case, sleep is that API since we're only interested in waiting for an amount of time.)

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        If you want a busy loop, just comment out the sleep line.
        This would not fulfil the requirement that at most three service calls must be done. For doing this, you also have to monitor the time (though you don't have to do it using a timer).

        Application where I would do a busy loop instead of using a sleep:

        • I'm running on a system where Time::HiRes is not available
        • I'm running on a system where there isn't going on much more critical stuff except my process, so I don't care eating CPU cycles by a busy loop
        • I find that doing one service call in average takes 0.3 seconds or longer, so I don't consider it worth saving cycles by doing micro-sleeps

        -- 
        Ronald Fischer <ynnor@mm.st>
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