http://qs1969.pair.com?node_id=303290

Nitrox has asked for the wisdom of the Perl Monks concerning the following question:

I've written an application that monitors the health of numerous servers and now I need to expand the "alerting" routine.

I'm trying to find the best way to store "windows of time" in a string (or an array of strings) (which is stored in a database and relates to the pager group that is responsible for that particular server). For example, "if server Foo fails and its currently Monday-Friday, 9:00-17:00 then page Group1".

The format that Swatch uses in it's config for the "when" option looked hopeful but only supports one "window". Here's an example: when=range_of_days:range_of_hours So if I wanted to be paged any time of the day on Saturday or Sunday the syntax would be: 7-1:1-24.

That works great for simplex windows but I already need to account for situations like: 

If Foo fails:
    AND its Mon-Sat (any hour)
    OR its Sun !6-8 (any hour except between 6-8am)
THEN
    page Group3

[download]
I also thought about utilizing the crontab syntax, so I went and read through the docs for many of the Schedule::Cron::* modules. Unfortunately I didn't see "the one" that I have envisioned in my head. I'd like to pass a crontab style string to the module and have it simply return true if the passed string would currently trigger an event.

Has anyone done any projects similar to this?

-Nitrox

Replies are listed 'Best First'.
Re: Representing windows of time in a string
by Limbic~Region (Chancellor) on Oct 30, 2003 at 17:03 UTC
    Nitrox,
    As I mentioned in the CB, The Panther has a section on using bitmap vectors to determine scheduling conflicts. It is just a matter of logically AND-ing the two bitmaps.

    Each hour in the week would be one bit. You would be storing a 21 byte bitmap vector. If the bit is set, then there is a problem if the event happens at this hour. The task then is to design a way to parse your range and localtime() into the bitmap vector.

    The following is very basic, but it gives you a fully functional framework. Expand it as you see fit.

    Read more... (1494 Bytes)

    I hope this helps - L~R

[reply]
[d/l]
      L~R, thanks for the full framework! I was headed down the same path and manipulated the examples from the Panther to work with 24 hours per day: 
      #!/usr/bin/perl -w
use strict;

my %base_hours = ( sun => 0, mon => 24, tue => 48, wed => 72 , thu => 
+96, fri => 120, sat => 144 );

my $vector = interval_parse("Sat 9-17, Sun 9-17");

my $bits = unpack("b*", $vector);

print $bits, "\n";

sub interval_parse {
    my ($interval_sequence) = @_;
    my ($time_range) = "";
    foreach my $day_hours (split /,/, $interval_sequence) {
       my ($day, $from, $to) = ($day_hours =~ /([A-Za-z]+).*(\d+)-(\d+
+)/);
       my $base = $base_hours{lc $day};
       $from += $base;
       $to += $base;
       
       for (my $i = $from; $i < $to;  $i++) {
           vec($time_range, $i, 1) = 1;
       }
    }
    return($time_range);
}

      [download]
      Thanks for the pointer!

      -Nitrox

[reply]
[d/l]
Re: Representing windows of time in a string
by simonm (Vicar) on Oct 30, 2003 at 16:50 UTC

    Strictly speaking, crontab schedules define "points" in time when the specific actions are triggered, whereas it seems you need a broader "range" or "set" of time spans.

    It might be overkill, but I think you should be able to accomplish this with the DateTime modules.

    For example, take a look at DateTime::Event::ICal... Using the ICal format, you could express your rules as: 

      my $incident = DateTime->from_epoch( time() ); # your data here
  
  my $ok_down = DateTime::Event::ICal->recur( byday=>["su"], byhour=>[
+6, 7] );
  
  unless ( $ok_down->contains( $incident ) {
    # notify 
  }

    [download]
[reply]
[d/l]
Re: Representing windows of time in a string
by davido (Cardinal) on Oct 30, 2003 at 17:11 UTC
    Advanced Perl Programming, otherwise known as the Panther book from O'Reilly & Assoc. has a discussion that you would probably find beneficial. Chapter two, section three:

    Consider that there are only 24 * 7 = 168 hours in a week, the entire week's schedule can be represented by a bitmap vector of 21 bytes (168 / 8) .... The other cool thing is that you can obtain time conflicts by logically AND-ing two bitmaps.

    The implementation example provided in the book uses vec to construct the bitmaps, and logical 'and' to check for overlaps.

    Hope this helps...


    Dave


    "If I had my life to live over again, I'd be a plumber." -- Albert Einstein
[reply]

Back to Seekers of Perl Wisdom