Locking log rotation for processing

reader.rb

require 'fileutils'

class Reader
  def self.read(filename, processing_filename)
    return [] unless File.exists?(filename)
    FileUtils.move(filename, processing_filename)
    lines = []
    File.open(processing_filename, 'r') do |f|
      f.flock(File::LOCK_EX)
      while !f.eof?
        lines << f.gets.chomp
      end
    end
    FileUtils.rm(processing_filename)
    lines
  end
end

lines = Reader.read('log', 'processing')

puts "Captured %4i lines: %4i - %4i" % [lines.size, lines[0], lines[-1]]

writer.rb

class Writer
  def initialize(filename, ttl)
    @filename = filename
    @ttl      = ttl
    reopen
  end

  def reopen
    @next_open_at = Time.now + @ttl
    @file.close if @file
    @file = File.open(@filename, 'a+')
    @file.flock(File::LOCK_SH)
  end

  def write(data)
    reopen if Time.now > @next_open_at
    @file.write(data)
    @file.flush
  end
end

w = Writer.new('log', 3)

i = 0
loop do
  i += 1
  w.write("#{i}\n")
  puts i
  sleep 0.5
end