module Thread::InheritableThreadVars::ThreadClassExtensions

def new(*, **, &block)
  parent = Thread.current
  super do |*args|
    child = Thread.current
    if child.instance_variable_defined?(:@thread_parent)
      # :nocov:
      raise "@thread_parent has already been declared elsewhere. Bailing out instead of clobbering it!"
      # :nocov:
    end
    child.instance_variable_set("@thread_parent", parent)
    block.call(*args)
  end
end