#!/usr/local/bin/ruby
# RenLock   -- filelock utility class
#
# usage:
#
#   lock = RenLock.new(dir, basename)
#   lock.lock {
#     ...
#   }
#
# another usage:
#
#   lock = RenLock.new(dir, basename)
#   lock.lock()
#     ...
#   lock.unlock()
#

class RenLockError < StandardError; end

class RenLock
  attr_accessor :timeout, :times, :sleep_time

  ## default
  SLEEP_TIME = 1
  TIMEOUT = 30
  TRY_TIMES = 5

  def initialize(dir, basename)
    @dir, @basename = dir, basename
    @timeout = TIMEOUT
    @times = TRY_TIMES
    @sleep_time = SLEEP_TIME
    @current = nil
    @path = @dir+'/'+@basename
  end

  def lock()
    @times.times{
      begin
	@current = current()
	File.rename(@path, @current)
	if iterator?
	  begin
	    yield
	  ensure
	    unlock()
	  end
	end
	return true
      rescue
	sleep @sleep_time
      end
    }
    delete_oldlock()
  end

  def delete_oldlock()
    @path = @dir+'/'+@basename
    Dir.foreach(@dir){|file|
      if file =~ /#{@basename}(\d+)/
	@current = current()
	if (Time.now.to_i - $1.to_i > @timeout)
	  begin
	    File.rename(@dir+'/'+file, @current)
	    if iterator?
	      begin
		yield
	      ensure
		unlock()
	      end
	    end
	    return true
	  rescue
	    # noop
	  end
	end
	raise RenLockError
      end
    }
    raise RenLockError
  end
  private :delete_oldlock

  def current()
    @path + Time.now.to_i.to_s
  end
  private :current

  def unlock()
    begin
      File.rename(@current, @path)
    rescue
      # noop
    end
  end

end  ## class RenLock

__END__

# Copyright 2001  TAKAHASHI 'Maki' Masayoshi (maki@open-news.com)
# all right reserved.
#
# This script are released under the same terms as Ruby.
#
# Special Thanks to:
#   OHZAKI Hiroki (`Perl memo' site)
#     http://www.din.or.jp/~ohzaki/perl.htm