foo.rb

require 'thread'

class Queue
  def timed_pop(timeout=0.5)
    @mutex.synchronize {
      while true
        if @que.empty?
          @waiting.push Thread.current
          raise Timeout::Error if @mutex.sleep(timeout) != 0
        else
          return @que.shift
        end
      end
    }
  end
end

q = Queue.new
Thread.new { sleep 0.1; q << 'hello!' }
puts q.timed_pop(0.5)

Output.txt

ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-darwin10.6.0]
~> ruby foo.rb
hello!
~> rvm use jruby
Using /Users/mperham/.rvm/gems/jruby-1.6.0
~> jruby -v
jruby 1.6.0 (ruby 1.8.7 patchlevel 330) (2011-03-15 f3b6154) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_24) [darwin-x86_64-java]
~> jruby foo.rb 
NoMethodError: undefined method `synchronize' for nil:NilClass
  timed_pop at foo.rb:5
     (root) at foo.rb:20
1 ~> jruby --1.9 foo.rb 
NoMethodError: undefined method `synchronize' for nil:NilClass
  timed_pop at foo.rb:5
     (root) at foo.rb:20