vendor/rails/activesupport/lib/active_support/core_ext/file/atomic.rb

   1 module ActiveSupport #:nodoc:
   2   module CoreExtensions #:nodoc:
   3     module File #:nodoc:
   4       module Atomic
   5         # Write to a file atomically.  Useful for situations where you don't
   6         # want other processes or threads to see half-written files.
   7         #
   8         #   File.atomic_write("important.file") do |file|
   9         #     file.write("hello")
  10         #   end
  11         #
  12         # If your temp directory is not on the same filesystem as the file you're
  13         # trying to write, you can provide a different temporary directory.
  14         #
  15         #   File.atomic_write("/data/something.important", "/data/tmp") do |f|
  16         #     file.write("hello")
  17         #   end
  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
  43       end
  44     end
  45   end
  46 end