Module: ActiveSupport::CoreExtensions::File::Atomic

Public Instance methods

atomic_write(file_name, temp_dir = Dir.tmpdir) {|temp_file| ...}

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.file") do |file|
    file.write("hello")
  end

If your temp 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("/data/something.important", "/data/tmp") do |f|
    file.write("hello")
  end

[Source]

    # File vendor/rails/activesupport/lib/active_support/core_ext/file/atomic.rb, line 18
18:         def atomic_write(file_name, temp_dir = Dir.tmpdir)
19:           require 'tempfile' unless defined?(Tempfile)
20: 
21:           temp_file = Tempfile.new(basename(file_name), temp_dir)
22:           yield temp_file
23:           temp_file.close
24: 
25:           begin
26:             # Get original file permissions
27:             old_stat = stat(file_name)
28:           rescue Errno::ENOENT
29:             # No old permissions, write a temp file to determine the defaults
30:             check_name = join(dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}")
31:             open(check_name, "w") { }
32:             old_stat = stat(check_name)
33:             unlink(check_name)
34:           end
35: 
36:           # Overwrite original file with temp file
37:           rename(temp_file.path, file_name)
38: 
39:           # Set correct permissions on new file
40:           chown(old_stat.uid, old_stat.gid, file_name)
41:           chmod(old_stat.mode, file_name)
42:         end

Methods

Public Instance methods