In-memory cache with key limit

memory_cache.rb

class MemoryCache

  DEFAULT_MAX_KEYS = 5000

  attr_reader :data, :max_keys

  def initialize(config)
    @data = {}
    @max_keys = config[:max_cache_keys] || DEFAULT_MAX_KEYS
    @lock = Mutex.new
  end

  def set(key, value)
    lock.synchronize do
      purge_cache
      data[String(key)] = value
    end
  end

  def get(key)
    data[String(key)]
  end

  def key?(string_key)
    data.key?(string_key)
  end

  def get_or_set(key, value = nil)
    string_key = String(key)

    if key?(string_key)
      get(string_key)
    else
      value = yield if block_given?
      set(string_key, value)
    end
  end

  private

  attr_reader :lock

  def purge_cache
    key_size = data.keys.size

    if key_size > max_keys
      # always remove about 1/3 of keys to reduce garbage collecting
      amount_of_keys = key_size / 3
      puts "Purging keys:#{key_size} by #{amount_of_keys}"

      data.keys.first(amount_of_keys).each { |key| data.delete(key) }
    end
  end

end