Is there a specific reason you cant handle it all in one script/thread/process instead?

use strict;
use warnings;

my %hash;

while(<DATA>){
    my ($key, $value) = split(/\s+/, $_);
    $hash{$key} = $value;
}

foreach(keys %hash){
    if ($_ =~ /this|is|a|test/){
        print "found string \"$_\" and its value is \"$hash{$_}\"\n";
    }
}

__DATA__
this 1
is 2
a 3
test 4
[download]

This would read a logfile and add all of its contents to the hash. Then you can do functions foreach key or value. Honestly, I wouldnt even use a hash or an array, I would just loop through the logfile and do functions foreach line. I cannot comment about threads as I never had any situation that I absolutely needed them myself.

Also, posting some form of code snippet or input data would help as well