method

atomic_write

v2.3.8 - Show latest stable - 0 notes - Class: ActiveSupport::CoreExtensions::File::Atomic

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What's this?

atomic_write(file_name, temp_dir = Dir.tmpdir) public

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

Show source

# File activesupport/lib/active_support/core_ext/file/atomic.rb, line 18
        def atomic_write(file_name, temp_dir = Dir.tmpdir)
          require 'tempfile' unless defined?(Tempfile)
          require 'fileutils' unless defined?(FileUtils)

          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

atomic_write

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