http://www.perlmonks.org?node_id=367162

eyepopslikeamosquito has asked for the wisdom of the Perl Monks concerning the following question:

This is the third installment of my Perl threads experiments. Again, I have something I don't understand and seek advice before perl-bugging it.

The test program below crashes for me on both Linux and Windows when you use an external sort function -- but not if you use an inline sort block. I am using Perl 5.8.4. Any explanations?

#!/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