class Gem::Resolv::Hosts

def each_address(name, &proc)
  lazy_initialize
  @name2addr[name]&.each(&proc)
end

def each_name(address, &proc)
  lazy_initialize
  @addr2name[address]&.each(&proc)
end

def getaddress(name)
  each_address(name) {|address| return address}
  raise ResolvError.new("#{@filename} has no name: #{name}")
end

def getaddresses(name)
  ret = []
  each_address(name) {|address| ret << address}
  return ret
end

def getname(address)
  each_name(address) {|name| return name}
  raise ResolvError.new("#{@filename} has no address: #{address}")
end

def getnames(address)
  ret = []
  each_name(address) {|name| ret << name}
  return ret
end

def initialize(filename = DefaultFileName)
  @filename = filename
  @mutex = Thread::Mutex.new
  @initialized = nil
end

def lazy_initialize # :nodoc:
  @mutex.synchronize {
    unless @initialized
      @name2addr = {}
      @addr2name = {}
      File.open(@filename, 'rb') {|f|
        f.each {|line|
          line.sub!(/#.*/, '')
          addr, *hostnames = line.split(/\s+/)
          next unless addr
          (@addr2name[addr] ||= []).concat(hostnames)
          hostnames.each {|hostname| (@name2addr[hostname] ||= []) << addr}
        }
      }
      @name2addr.each {|name, arr| arr.reverse!}
      @initialized = true
    end
  }
  self
end