module Tins::ThreadLocal

def thread_local(name, default_value = nil)

value _value_ is given, it is used to initialize the variable.
Define a thread local variable named _name_ in this module/class. If the 
def thread_local(name, default_value = nil)
  is_a?(Module) or raise TypeError, "receiver has to be a Module"
  name = name.to_s
  my_id = "__thread_local_#{__id__}__"
  ObjectSpace.define_finalizer(self, @@cleanup)
  define_method(name) do
    Thread.current[my_id] ||= {}
    Thread.current[my_id][name]
  end
  define_method("#{name}=") do |value|
    Thread.current[my_id] ||= {}
    Thread.current[my_id][name] = value
  end
  if default_value
    Thread.current[my_id] = {}
    Thread.current[my_id][name] = default_value
  end
  self
end