Using Alarm to Handle Timing

[chromatic]

As the Perl threads implementation is still undergoing renovation, I've considered other approaches for handling issues of concurrency.

In one of my programs, it would be very useful to have certain tasks executed at certain times. Low-latency and real-time responses aren't critical, but if they happen within a few seconds either way, I'm happy.

Here's an approach I'm testing. Things work fine with my test, but I'd like to know if there are any problems with my concept or execution. Alternately, if there's a better way to do this, feel free to let me know. (Using a separate process or cron is a possibility, but it hampers porting, which is important with this project).

#!/usr/bin/perl -w

use strict;

# we're abusing signals for this trick
$SIG{ALRM} = \&wake_up;
start();

sub start {
    # arbitrary number, could be a variable
    alarm(5);
    while (1) {
        # random time so the handler executes in different spots
        sleep int rand(3);
        print "Here's a line after a sleep.\n";
        sleep int rand(3);
        print "Here's a line after another sleep.\n";
        
        # don't interrupt this chunk
        my $hold = alarm(0);
        print "Suspending alarm with $hold second(s) left.\n";
        sleep int rand(3);
        print "There should never be an alarm right before this.\n";
        
        # interruptions okay now
        alarm($hold);
        sleep int rand(3);
        print "This is the last line of the loop.\n\n";
    }
}

sub wake_up {
    # don't interrupt the interrupt (probably unnecessary)
    $SIG{ALRM} = 'ignore';
    print "\t=> in alarm handler <=\n";
    # reset alarm
    alarm(5);
    # reinstall handler
    $SIG{ALRM} = \&wake_up;
}