#!/usr/bin/perl
use strict;              
use warnings;            
                         
my %Jobs = (             
    Action1 => { status=>'READY', },                                            
    Action1a=> { status=>'READY', prereqs => [ qw(Action1) ], },
    Action2 => { status=>'READY', },
    Action2a=> { status=>'READY', prereqs => [ qw(Action2) ], },
    Action3 => { status=>'READY', prereqs => [ qw(Action1a Action2a) ], },
    Action4 => { status=>'READY', prereqs => [ qw(Action3) ], },
);                       
                         
my @task_list = sort keys %Jobs;
                         
my $cnt=0;               
while (@task_list) {     
    ++$cnt;              
    print "\nTIME: $cnt\n";
    for (sort keys %Jobs) {
        printf "%-16.16s %-10.10s %u\n",
            $_, $Jobs{$_}{status}, is_ready($_);
    }                    
                         
    # Clean out the items that are already done
    @task_list = grep { $Jobs{$_}{status} ne 'DONE' } @task_list;
                         
    # Each time we wake up, get list of tasks ready to go and fire
    # them off           
    my @ready = grep { is_ready($_) } @task_list;
    $Jobs{$_}{status}="RUNNING" for @ready;
                         
    # Fake code to pretend to monitor tasks & update job list
    for (@task_list) {   
        $Jobs{$_}{status}="DONE"
           if $Jobs{$_}{status} eq "RUNNING" and rand() < 0.25;
    }                    
    sleep 1;             
}                        
                         
sub is_ready {           
    my $task=shift;      
    return 0 if $Jobs{$task}{status} ne 'READY';
    return 1 if ! exists $Jobs{$task}{prereqs};
    for (@{$Jobs{$task}{prereqs}}) {
        return 0 if $Jobs{$_}{status} ne 'DONE';
    }                    
    return 1;            
}