C:\>perl -Mthreads -e "my $t = threads->new( sub {} ); $t->join; $t->join;die 2"
Thread already joined at -e line 1.

##</code><code>##

C:\>perl -Mthreads -e "my $t = threads->new( sub {} ); $t->join; eval{$t->join};warn $@;die 2"
Thread already joined at -e line 1.
2 at -e line 1.