class ThreadSafe::Cache

def [](key)
  if value = super # non-falsy value is an existing mapping, return it right away
    value
  # re-check is done with get_or_default(key, NULL) instead of a simple !key?(key) in order to avoid a race condition, whereby by the time the current thread gets to the key?(key) call
  # a key => value mapping might have already been created by a different thread (key?(key) would then return true, this elsif branch wouldn't be taken and an incorrent +nil+ value
  # would be returned)
  # note: nil == value check is not technically necessary
  elsif @default_proc && nil == value && NULL == (value = get_or_default(key, NULL))
    @default_proc.call(self, key)
  else
    value
  end
end

def each_key
  each_pair {|k, v| yield k}
end unless method_defined?(:each_key)

def each_value
  each_pair {|k, v| yield v}
end unless method_defined?(:each_value)

def empty?
  each_pair {|k, v| return false}
  true
end unless method_defined?(:empty?)

def fetch(key, default_value = NULL)
  if NULL != (value = get_or_default(key, NULL))
    value
  elsif block_given?
    yield key
  elsif NULL != default_value
    default_value
  else
    raise_fetch_no_key
  end
end

def fetch_or_store(key, default_value = NULL)
  fetch(key) do
    put(key, block_given? ? yield(key) : (NULL == default_value ? raise_fetch_no_key : default_value))
  end
end

def initialize(options = nil, &block)
  if options.kind_of?(::Hash)
    validate_options_hash!(options)
  else
    options = nil
  end
  super(options)
  @default_proc = block
end

def initialize_copy(other)
  super
  populate_from(other)
end

def key(value)
  each_pair {|k, v| return k if v == value}
  nil
end unless method_defined?(:key)

def keys
  arr = []
  each_pair {|k, v| arr << k}
  arr
end unless method_defined?(:keys)

def marshal_dump
  raise TypeError, "can't dump hash with default proc" if @default_proc
  h = {}
  each_pair {|k, v| h[k] = v}
  h
end

def marshal_load(hash)
  initialize
  populate_from(hash)
end

def populate_from(hash)
  hash.each_pair {|k, v| self[k] = v}
  self
end

def put_if_absent(key, value)
  computed = false
  result = compute_if_absent(key) do
    computed = true
    value
  end
  computed ? nil : result
end unless method_defined?(:put_if_absent)

def raise_fetch_no_key
  raise KeyError, 'key not found'
end

def size
  count = 0
  each_pair {|k, v| count += 1}
  count
end unless method_defined?(:size)

def validate_options_hash!(options)
  if (initial_capacity = options[:initial_capacity]) && (!initial_capacity.kind_of?(0.class) || initial_capacity < 0)
    raise ArgumentError, ":initial_capacity must be a positive #{0.class}"
  end
  if (load_factor = options[:load_factor]) && (!load_factor.kind_of?(Numeric) || load_factor <= 0 || load_factor > 1)
    raise ArgumentError, ":load_factor must be a number between 0 and 1"
  end
end

def value?(value)
  each_value do |v|
    return true if value.equal?(v)
  end
  false
end unless method_defined?(:value?)

def values
  arr = []
  each_pair {|k, v| arr << v}
  arr
end unless method_defined?(:values)