instance_variable_on_singleton.rb

class Foo

  def self.set(params)
    puts "setting myparams = #{params}"
    @my_params = params
  end

  def self.save_str
    puts "my_param: '#{@my_params}'"
    sleep(1)
    puts "my_param: '#{@my_params}' (still in the same method call)"
  end

end
Foo.set 'one'
Thread.new{Foo.save_str}
Foo.set 'two'
sleep(3) # just to keep the script alive while save_str is performed

## output when runned.

setting myparams = one
my_param: 'one'
setting myparams = two
my_param: 'two' (still in the same method call)