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

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