Threadz not finishing

gistfile1.rb

require 'rubygems'
require 'threadz'

def dostuff(i)
  sleep 1
  raise "Exception" if i == 4
end

tp = Threadz::ThreadPool.new
batch = tp.new_batch

[1,2,3,4,5].each do |i|
  batch << lambda { dostuff(i) }
end

puts "Wait"
batch.wait_until_done
puts "Comes here"