In 1.9 mode Enumerator.new spins up a new Generator instance along with a thread...
I discovered this bug when evaluating lazy list options in Ruby. The `Denumerable` class from the facets gem provided an option so I was benchmarking the performance of it. Here are the benchmarks revlaling how slow 1.9 mode is in dealing with Enumerator.new and Enumerator#next: https://gist.github.com/1145736
In 1.8 mode JRuby performs well since it is using the monkeypatched version of Enumerator that facets provides: https://github.com/rubyworks/facets/blob/master/lib/core/facets/enumerator.rb#L37-44
See the IRC log discussion with headius and mabes: http://logs.jruby.org/jruby/2011-08-15.html#T18-44-37