Method: File.atomic_write

Defined in:
lib/core/facets/file/atomic_write.rb

.atomic_write(file_name, temp_dir = nil) {|temp_file| ... } ⇒ Object

Write to a file atomically. Useful for situations where you don’t want other processes or threads to see half-written files.

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

If your temporary directory is not on the same filesystem as the file you’re trying to write, you can provide a different temporary directory.

File.atomic_write("important.txt", "tmp") do |file|
  file.write("hello")
end

NOTE: This method is not a common core extension and is not loaded automatically when using require 'facets'.

CREDIT: David Heinemeier Hansson

Yields:

  • (temp_file)

Uncommon:

  • require ‘facets/fileutils/atomic_write’



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# File 'lib/core/facets/file/atomic_write.rb', line 32

def self.atomic_write(file_name, temp_dir=nil)
  temp_dir  = temp_dir || Dir.tmpdir
  temp_file = Tempfile.new(basename(file_name), temp_dir)

  yield temp_file
  temp_file.close

  begin
    ## Get original file permissions
    old_stat = stat(file_name)
  rescue Errno::ENOENT
    ## No old permissions, write a temp file to determine the defaults
    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

  ## Overwrite original file with temp file
  FileUtils.mv(temp_file.path, file_name)

  ## Set correct permissions on new file
  chown(old_stat.uid, old_stat.gid, file_name)
  chmod(old_stat.mode, file_name)
end