# File src/ruby_supportlib/phusion_passenger/vendor/daemon_controller/lock_file.rb, line 80
    def shared_lock
      File.open(@filename, 'w+') do |f|
        if Fcntl.const_defined? :F_SETFD
          f.fcntl(Fcntl::F_SETFD, Fcntl::FD_CLOEXEC)
        end
        f.flock(File::LOCK_SH)
        yield
      end
    end