In theory and somewhat in practice Perl 6 neatly handles this for you with Supplies and taps handling signals in a thread safe sort of way. See "System events exposed as Supplies" in the Perl 6 design documents. The Perl 6 solution inspired me to write some Perl 5 code with similar capability that I have included below. Note that like the Perl 6 solution my code will "as is" do the actual handling of SIGINTs sequentially but it should be quite easy to add some parallel threads if wanted.

use strict;
use warnings;

use threads;
use Thread::Queue;

my $q = Thread::Queue->new();    # A new empty queue
my $thr = threads->create(
    sub {
        # Thread will loop until no more work
        while (defined(my $item = $q->dequeue())) {
            print "starting work on $item\n";
            sleep 5;
            print "finished work on $item\n";
        }
    }
);

my $item = 1;
{
    local $SIG{INT} = sub { $q->enqueue($item++) };
    kill 'INT', $$;
    sleep 2;
    kill 'INT', $$;
    sleep 2;
}
$q->enqueue(undef); # I think in more modern Thread::Queue has $q->end
$thr->join();
[download]