Threading problems... help?

perm.rb

#!/usr/bin/ruby

require 'openssl'
require 'base64'
require 'rubygems'
require 'aws'

# Open master s3 connection
master_s3 = Aws::S3.new(
 'key',
 'secret_key'
)

# Setup queue
q = Queue.new

# Select the bucket
bucket = master_s3.bucket('assets-bucket-name')

# Iterate over the keys
bucket.keys.each do |key|
  while q.size >= 60
    puts "sleeping because queue size is #{q.size}"
    sleep 1
  end

  q << Thread.new(key) do |key|
    puts "Working on #{key}"    
    Aws::S3::Grantee.new(key, 'user_id_of_cloudfront_user', 'READ', :apply)
    q.pop
  end
end

# It freezes here... but only after multiple thousands of threads...
until q.empty?
  sleep 1
end