Class: AtomicFile

Inherits:
File show all
Defined in:
lib/supplemental/facets/atomicfile.rb

Overview

This is a precursor to the possibility of a more extensive Atomic File I/O system. For now it simply provides a means for atomic file writing.

Class Method Summary collapse

Methods inherited from File

append, create, ext, null, read_binary, read_list, rewrite, rewrite!, rootname, sanitize, split_all, split_root, writelines, yaml?

Class Method Details

.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.

AtomicFile.write("tmp/important.file") 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.

AtomicFile.write("tmp/something.important", "tmp") do |file|
  file.write("hello")
end

Yields:

  • (temp_file) 


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# File 'lib/supplemental/facets/atomicfile.rb', line 23

def self.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