What Ruby version does ruby-doc.org refer to? The main page has links to
1.8.6, 1.8.7, and 1.9. Following 1.8.6 for Thread takes me to
http://www.ruby-doc.org/core/classes/Thread.html which lists
Thread.exclusive as an api. However, MRI 1.8.6 does not have such an
api. There are no RubySpecs for it either.