class File

def self.atomic_write(file_name, temp_dir = dirname(file_name))

end
file.write('hello')
File.atomic_write('/data/something.important', '/data/tmp') do |file|

same physical filesystem as the file you're trying to write.
behavior you can provide a different directory but it must be on the
in the same directory as the destination file. If you don't like this
This method needs to create a temporary file. By default it will create it

end
file.write('hello')
File.atomic_write('important.file') do |file|

want other processes or threads to see half-written files.
Write to a file atomically. Useful for situations where you don't 
def self.atomic_write(file_name, temp_dir = dirname(file_name))
  require "tempfile" unless defined?(Tempfile)
  Tempfile.open(".#{basename(file_name)}", temp_dir) do |temp_file|
    temp_file.binmode
    return_val = yield temp_file
    temp_file.close
    old_stat = if exist?(file_name)
      # Get original file permissions
      stat(file_name)
    else
      # If not possible, probe which are the default permissions in the
      # destination directory.
      probe_stat_in(dirname(file_name))
    end
    if old_stat
      # Set correct permissions on new file
      begin
        chown(old_stat.uid, old_stat.gid, temp_file.path)
        # This operation will affect filesystem ACL's
        chmod(old_stat.mode, temp_file.path)
      rescue Errno::EPERM, Errno::EACCES
        # Changing file ownership failed, moving on.
      end
    end
    # Overwrite original file with temp file
    rename(temp_file.path, file_name)
    return_val
  end
end

def self.probe_stat_in(dir) # :nodoc:

:nodoc:
Private utility method. 
def self.probe_stat_in(dir) # :nodoc:
  basename = [
    ".permissions_check",
    Thread.current.object_id,
    Process.pid,
    rand(1000000)
  ].join(".")
  file_name = join(dir, basename)
  FileUtils.touch(file_name)
  stat(file_name)
rescue Errno::ENOENT
  file_name = nil
ensure
  FileUtils.rm_f(file_name) if file_name
end