How to check Queue status?

gistfile1.txt

#!/usr/bin/env ruby

q1 = Queue.new
q2 = Queue.new

t1 = Thread.new do
  q2 << (q1.pop + " World")
end

t2 = Thread.new do
  sleep 1
  q1 << "Hello"
end

while ! q2.empty?
  p q2.pop # <<< THIS NEVER HAPPENS
end

p q2.pop

t1.join
t2.join