use threads;
use strict;

my @fpaths = ('fpath1', 'fpath2');
my %fdata;
foreach (@fpaths) {
    my $data;
    my $child = threads->new(\&check_file, $_, $fdata{$_} = \$data);
}

sub check_file {
    my ($fpath, $arrp) = @_;
    my $handle;
    while (!-e $fpath || !open($handle, $fpath)) { sleep(1); }
    $$arrp = join('', <$handle>);
    close($handle);
}