Module Uwt.Handle_fileno

The usage of fileno is unsafe and strongly discouraged. But it's sometimes necessary, if you need to interact with third parties libraries. Rules:

• You must still keep your original handle around. Otherwise uwt will close the handle when the garbage collector removes it.

• Always close the handle with Handle.close (or Tcp.close, etc.), not Unix.close or any other function.

• Never pass the file descriptor to functions like Pipe.openpipe or Poll.start.