package uwt

Handles are closed automatically, if they are not longer referenced from the OCaml heap. Nevertheless, you should nearly always close them with close, because:

• if they wrap a file descriptor, you will sooner or later run out of file descriptors. The OCaml garbage collector doesn't give any guarantee, when orphaned memory blocks are removed.

• you might have registered some repeatedly called action (e.g. timeout, read_start,...), that prevent that all references get removed from the OCaml heap.

However, it's safe to write code in this manner:

let s = Uwt.Tcp.init () in
let c = Uwt.Tcp.init () in
Uwt.Tcp.nodelay s false;
Uwt.Tcp.simultaneous_accepts true;
if foobar () then (* no file descriptor yet assigned, no need to worry
                     about exceptions inside foobar,... *)
  Lwt.return_unit (* no need to close *)
else
  ...

If you want - for whatever reason - keep a file descriptor open for the whole lifetime of your process, remember to keep a reference to its handle.

Prefer close or close_noerr to close_wait. close or close_noerr return immediately (there are no useful error messages, beside perhaps a notice, that you've already closed that handle).

close_wait is only useful, if you intend to wait until all concurrent write and read threads related to this handle are canceled.

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 orginal handle around. Otherwise uwt will close the handle ....

• close the handle always with Handle.close, not Unix.close or any other function

• Don't pass the file descriptor to functions like Pipe.openpipe or Poll.start