If you comment out the Thread.pass in this example, under Ruby 1.9.2 at least, the producer runs forever and the consumers never run (or at least don't run until the producer is completely done). WTF?

toy_threads.rb

#!/usr/bin/env ruby

require 'thread'

work = Queue.new
producer = Thread.new do
  (1..10000).each do |i|
    work << i
    sleep 0.1
    puts "P: #{Thread.current.inspect}"
    Thread.pass
  end
end

shutdown = false
consumer = []
2.times do |i|
  consumer << Thread.new do
    while shutdown == false
      item = work.pop
      puts "Processing #{item}"
      Thread.pass
      puts "C: #{Thread.current.inspect}"
    end
  end
end

puts "M: #{Thread.current.inspect}"

Thread.pass
producer.join
while !work.empty?
  sleep 0.1
end

shutdown = true
consumer.each {|x| x.kill}
consumer.each {|x| x.join}

exit 0