Perl running two while loop subroutines in parallel

I am looking to run two subroutines in parallel, where both perform the same task on an android handset using ADB commands. With help from SO and other research I have produced the following code below, however I am new to multithreading and I get an error of 'Free to wrong pool' during execution. I am assuming I get this as I am using the $_ variable in both threads, is this correct? I am using Windows7 to run this, but my Perl interpreter crashes on running this script. Any guidance would be greatly appreciated. Thanks.

use strict;
use Win32::OLE;
use EFS_Handle;
use HelperFunctions;
use threads;

#### Various ADB command sequences follow ####
#### Start of multithread to run the same function on different android handsets ####

my @jobs;

push @jobs, threads->create(
    sub {
        print "\n\t" . curTime() . " :\t DUT Time at start of MPLMN search";

        open my $fh1, '>', "output.txt" or die "Cannot open output.txt: $!";
        my $pid1 = open my $log1, "-|", "adb -s 42d8d7dd logcat";

        system('adb -s 42d8d7dd shell input keyevent KEYCODE_ENTER');

        while (<$log1>) {
            $fh1->print($_);
            last if m/Sorted scan results/;
        }
        kill "TERM", $pid1;
        close $log1;
        print "\n\t" . curTime() . " :\t DUT Time at End of MPLMN search\n";
    }
);

push @jobs, threads->create(
    sub {
        print "\n\t" . curTime() . " :\t REF Time at start of MPLMN search";

        open my $fh, '>', "output.txt" or die "Cannot open output.txt: $!";
        my $pid = open my $log, "-|", "adb -s 0123456789ABCDEF logcat";

        system('adb -s 0123456789ABCDEF shell input keyevent KEYCODE_ENTER');

        while (<$log>) {
            $fh->print($_);
            last if m/EVENT_NETWORK_SCAN_COMPLETED/;
        }
        kill "TERM", $pid;
        close $log;
        print "\n\t" . curTime() . " :\t REF Time at End of MPLMN search\n";

    }
);

$_->join for @jobs;