--- /dev/null
+require 'tempfile'
+
+module ActiveSupport #:nodoc:
+ module CoreExtensions #:nodoc:
+ module File #:nodoc:
+ module Atomic
+ # 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
+ def atomic_write(file_name, 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 = ".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
+ rename(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
+ end
+ end
+ end
+end