I was wondering how one may perform a given action every x seconds (or other, perhaps smaller) unit of time. My most logical answer is using Time::HiRes to sleep for x milliseconds, minus the ones the action took us to perform. This involves getting the current time a lot, to see how late we are, and all that.

Operations are possibly blocking, so they may take quite a bit of real time. Doing that seems ridiculusly wasteful, because there are so many system calls. But there is a reason - accuracy can fluxuate, but shouldn't accumilate fluxuations - simply sleeping for a constant time unit is not an option. In other words i'd like the script to correct it's timed interval so that it's somewhat in sync with the system clock.

My idea was something like this (say we want every second, maintaining relative accuracy for periods of a year or so): 

my $x = 10; # the number of iterations to do between each sync
my $int = 10; # the desired interval between actions
my $y = 0; # another iteration limit, for catching up


foo: {
    
    my $time = time();
    
    for (my $i = 0; $i <= $y; $i++){ # catch up with real time from th
+e last loop
        action(); # perform the action
    }

    for (my $i = 0; $i < $x; $i++){
        action();
        sleep $int;
    }

    my $ntime = time();
    
    $y = int ( ($ntime - $time - $x * $int) / $int ); # calculate how 
+many we missed, and round down

    redo foo;
}

[download]
Any suggestions?

-nuffin
zz zZ Z Z #!perl

In reply to Accurately timed reccuring events by nothingmuch

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