module Concurrent::Synchronization::AbstractStruct

def pr_underscore(clazz)
  word = clazz.to_s.dup # dup string to workaround JRuby 9.2.0.0 bug https://github.com/jruby/jruby/issues/5229
  word.gsub!(/::/, '/')
  word.gsub!(/([A-Z]+)([A-Z][a-z])/,'\1_\2')
  word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
  word.tr!("-", "_")
  word.downcase!
  word
end