Enumerator#each on enumerators created with Enumerator.new in 1.9 mode is slow

The problem here was that the Enumerator.new { } form automatically created a Generator to pump the block. Our Generator by default uses a Thread to pump the block it has been given, and so performance took a hit.

I have a patch locally that appears to fix the problem; essentially, it introduces the "Yielder" class we were missing and uses that for Generator#each rather than the "next" logic which requires a native thread. So far it's passing specs, so it might get into 1.6.4.

More information while I run tests.

Generator is implemented entirely in Ruby, using a Thread, a SizedQueue for transferring values, and finalization to clean everything up if the containing Enumerator gets collected. Normally we only spin up a generator when someone calls Enumerator#next. At this point, we have an eachable object and can choose to use cheaper non-threaded Generator impls. However the Enumerator.new {} form created a threaded generator immediately since the given block has no eachable container. And the threaded generator always used threaded "nexting" logic, even for internal iteration with #each.

My fix (still being tested) introduces the Yielder class and uses instances of that with no threading to implement Generator#each. The idea is that since each (with a block) is explicitly internal iteration, there's no need to spin up a thread for external iteration.

jruby-1_6 and master:

commit a7bc0e77d3bea75fbb1112465bfc515d0a8a1662
Author: Charles Oliver Nutter <headius@headius.com>
Date:   Mon Aug 15 14:48:43 2011 -0500

    Fix JRUBY-5998: Enumerator#each on enumerators created with Enumerator.new in 1.9 mode is slow
    
    Enumerator.new{} form always creates a Generator, just like 1.9.2 does. However, it creates the default Generator form that uses a thread to drive the 
    
    * Use simple internal iteration rather than threaded "nexting" for Enumerator.new{}.each{}
    * Fix a bug in Enumerable#chunk caused by bad arity specification, which caused breakage under non-threaded form

commit 50b6b3caa5134156dd418e3a56292aa1ecc53f23
Author: Charles Oliver Nutter <headius@headius.com>
Date:   Mon Aug 15 14:48:43 2011 -0500

    Fix JRUBY-5998: Enumerator#each on enumerators created with Enumerator.new in 1.9 mode is slow
    
    Enumerator.new{} form always creates a Generator, just like 1.9.2 does. However, it creates the default Generator form that uses a thread to drive the 
    
    * Use simple internal iteration rather than threaded "nexting" for Enumerator.new{}.each{}
    * Fix a bug in Enumerable#chunk caused by bad arity specification, which caused breakage under non-threaded form