#!/usr/bin/perl -w

use strict;
use threads;
$|=1;

sub mycmp { length($b) <=> length($a) }

sub do_one_thread {
   my $kid = shift;
   warn "kid $kid before sort\n";
   my @list = ( 'x', 'yy', 'zzz', 'a', 'bb', 'ccc', 'aaaaa', 'z',
                'hello', 's', 'thisisalongname', '1', '2', '3',
                'abc', 'xyz', '1234567890', 'm', 'n', 'p' );
   for my $j (1..1000) {
      # This does not crash
      # for my $k (sort { length($b) <=> length($a) } @list) {}
      # Yet this does
      for my $k (sort mycmp @list) {}
   }
   warn "kid $kid after sort\n";
}

sub do_threads {
   my $nthreads = shift;
   my @kids = ();
   for my $i (1..$nthreads) {
      my $t = threads->new(\&do_one_thread, $i);
      warn "parent $$: continue\n";
      push(@kids, $t);
   }
   for my $t (@kids) {
      warn "parent $$: waiting for join\n";
      $t->join();
      warn "parent $$: thread exited\n";
   }
}

# do_threads(1);      # does not crash
do_threads(2);        # crashes