def atomic_write(file_name, temp_dir = Dir.tmpdir)
require 'tempfile' unless defined?(Tempfile)
require 'fileutils' unless defined?(FileUtils)
temp_file = Tempfile.new(basename(file_name), temp_dir)
yield temp_file
temp_file.close
begin
old_stat = stat(file_name)
rescue Errno::ENOENT
check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
open(check_name, "w") { }
old_stat = stat(check_name)
unlink(check_name)
end
FileUtils.mv(temp_file.path, file_name)
chown(old_stat.uid, old_stat.gid, file_name)
chmod(old_stat.mode, file_name)
end