source: trunk/essentials/dev-lang/perl/ext/Thread/lock.tx

BEGIN {
    eval { require Config; import Config };
    if ($@) {
        print "1..0 # Skip: no Config\n";
        exit(0);
    }
}

use Thread;

$level = 0;

sub worker
{
    my $num = shift;
    my $i;
    print "thread $num starting\n";
    for ($i = 1; $i <= 20; $i++) {
        print "thread $num iteration $i\n";
        select(undef, undef, undef, rand(10)/100);
        {
            lock($lock);
            warn "thread $num saw non-zero level = $level\n" if $level;
            $level++;
            print "thread $num has lock\n";
            select(undef, undef, undef, rand(10)/100);
            $level--;
        }
        print "thread $num released lock\n";
    }
}

for ($t = 1; $t <= 5; $t++) {
    new Thread \&worker, $t;
}