#! /usr/bin/perl
use threads;
use threads::shared;
$|=1;
{
my $l : shared;  # private lexical
sub f() {
  lock($l);      # any f() in any thread is "locked"
  my $tid = threads->tid();
  print "A}$tid}$_[0]\n";
  select undef, undef, undef, rand(2);
  print "B}$tid}$_[0]\n";
}
} # -- end scope for $l

threads->create(\&f, $_) for (qw|foo bar baz|);
$_->join() for threads->list();
__END__