If you don't need to share any variables or anything, my Async::Event::Interval can help you. It forks off a separate process and performs work outside of the main process based on a callback subroutine within the script (you can name this sub whatever you want). Here's a basic example. The 1 in the call to new() is how often the event fires, in seconds (floating point seconds work), so for 30 minutes, you'd put 1800. The callback sub is the work you want the event to do. I've tested it on Strawberry perl v5.24.1, and the same version on Linux.

use warnings;
use strict;

use Async::Event::Interval;
 
my $event
    = Async::Event::Interval->new(1, \&callback);
 
$event->start;

my $c = 1;

while (1){
    print "$c: in the main process...\n";
    $c++;
    sleep 10;
}

sub callback {
    print "we're alive!\n";
}
[download]

Output:

1: in the main process...
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
we're alive!
2: in the main process...
we're alive!
we're alive!
[download]

Thanks for you response, I will give this a try and see if it gives me what I want<\p>

Perhaps you could use alarm (but see this for portability issues) to trigger a $SIG{ ALRM } callback that sends the "I'm alive" message.

Update: Corrected mis-matched brackets in text.

To answer your question as stated, I would look first at an event loop, which in my preference would be AnyEvent. You might particularly consider the section in the tutorial headed Timers and other event sources to implement your 30-minute schedule.

The second function is for the script to send an "I'm alive" email every 30 mins or so

That, however is the intriguing part. I cannot think why you would want this - it sounds much more likely that you'd want to be alerted every 30 minutes or so if it wasn't alive - ie. in normal operation it's quiet, but when it is not running you receive an "I'm dead" email.

Either way the trivial solution is not a Perl one but an O/S one: a cron job to run every 30 minutes which checks the process is running and sends your email if it is (or is not, as preferred).

Thanks, I will have a look at AnyEvent and I agree with your comment about the alert email if the script isn't running but that is not what the user requested.

I also wish it was a Linux machine so I can use cron but the script will be running in Windows and the request was for a "simple, single program" solution to use their words.<\p>

I also wish it was a Linux machine so I can use cron

FYI, Windows does have a chron "equivalent". It is called Task Scheduler. It has both a Windows and a command line interface. Something like "run program X every 30 minutes" is possible. I've used Task Scheduler to periodically run a Perl script before without problems.

Update with a few comments and considerations: I wouldn't necessarily interpret the user request for "one program" as a hard and fast design implementation limitation. It appears that the main point appears to be something reliable. Simple often, but not always yields reliable.

For the "wait for emergency" function, you could have a simple loop that does blocking I/O on that port while waiting for the "Emergency" message. If you get messages fairly regularly that are not "emergencies", blocking I/O would fine fine.

For the once per 30 minute "watchdog on the monitor for emergency" function. In applications that I've worked on, more than the "process is running" is often required. The thing to be verified is: "is the thing that is monitoring for an emergency" really doing actual work(processing messages looking for an emergency)? You could have the main monitoring function do something that is observable by the "watchdog" process. Perhaps simply incrementing the name of a zero length file for every message it looks at? If the watchdog function determines that no messages are being processed by the monitoring function, it would conclude that something is amiss in addition to making sure that the monitor process is actually "running", i.e. in the process table.

You may find the select method shown by tybalt89 in Re: UDP Client and Server in one of interest too

Based on my understanding on reading your problem, you are trying to do two things with a single script.

I may go for,
For first point - Schedule a cron job for every minute and do the monitoring stuff using perl script (you may select monitor option while running the script by passing argument as monitor)
For second point - Schedule a cron job for every 30 minutes and send alert email using perl script(you may select alert option while running the same script by passing argument as alert)

For last one "how to convert it into exe" - Please use PP you can look into one of the recent post by marto here
Re: How to convert bunch of perl file + other dependent Input files Into a single executable