class Concurrent::AbstractThreadLocalVar

def allocate_storage
  raise NotImplementedError
end

def bind(value, &block)
  if block_given?
    old_value = self.value
    begin
      self.value = value
      yield
    ensure
      self.value = old_value
    end
  end
end

def default
  if @default_block
    self.value = @default_block.call
  else
    @default
  end
end

def initialize(default = nil, &default_block)
  if default && block_given?
    raise ArgumentError, "Cannot use both value and block as default value"
  end
  if block_given?
    @default_block = default_block
    @default = nil
  else
    @default_block = nil
    @default = default
  end
  allocate_storage
end

def value
  raise NotImplementedError
end

def value=(value)
  raise NotImplementedError
end