class File

def self.probe_stat_in(dir) # :nodoc:
  basename = [
    ".permissions_check",
    Thread.current.object_id,
    Process.pid,
    rand(1000000)
  ].join(".")
  file_name = join(dir, basename)
  FileUtils.touch(file_name)
  stat(file_name)
rescue Errno::ENOENT
  file_name = nil
ensure
  FileUtils.rm_f(file_name) if file_name
end