I'd use a global shared hash rather than a "singleton object" which is just a fancy name for a global anyway, and gets you into a painful world of shared methods.

Simple and effective, I'd do it like this:

#! perl -slw
use strict;
use threads;
use threads::shared;
use Data::Dump qw[ pp ];
use Time::HiRes qw[ time sleep ];

my $sem :shared;
sub tprint {
    lock $sem;
    print @_;
}

my %config :shared;

sub loadConfig{
    open my $fh, '<', 'junk.config' or die $!;
    lock %config;
    $config{ $_->[0] } = $_->[1] while @{ $_ = [ split ':', <$fh> ] };
    tprint pp \%config;
    tprint "Config refreshed at ", scalar time;
};

$SIG{'INT'} = \&loadConfig;

sub worker {
    my $tid = threads->tid;
    my $telltale = $config{ telltale };
    while( sleep 0.01 ) {
        if( $config{ telltale } ne $telltale ) {
            tprint "[$tid] saw change at ", scalar time();
            $telltale = $config{ telltale };
        }
    }
}

loadConfig();

my @workers = map threads->create( \&worker ), 1 .. 8;

while( threads->list > 1 ) {
    $_->join for threads->list( threads::joinable );
    sleep 0.1;
}


__END__
C:\test>921884.pl
{
  # tied threads::shared::tie
  bill => "leprechaun\n",
  fred => 123
      ,
  telltale => 1
      ,
}
Config refreshed at 1314106074.357
{
  # tied threads::shared::tie
  bill => "leprechaun\n",
  fred => 123
      ,
  telltale => 2
      ,
}
[3] saw change at 1314106084.6591
[4] saw change at 1314106084.66004
[5] saw change at 1314106084.66113
[6] saw change at 1314106084.66309
[1] saw change at 1314106084.66507
[7] saw change at 1314106084.66507
[2] saw change at 1314106084.66612
[8] saw change at 1314106084.66705
Config refreshed at 1314106084.66944
Terminating on signal SIGBREAK(21)
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