[ruby-core:100072] Re: [Ruby master Feature#17059] epoll as IO.select

[e-mail] wrote:
> Feature #17059: epoll as IO.select
> https://bugs.ruby-lang.org/issues/17059

Try ppoll(2) to replace IO.select, instead.  It also works on
newer FreeBSD.

To use epoll(7) effectively, you really need a scheduler API and
probably restructure programs.  Furthermore, the Level-Triggered
(default) epoll behavior seems to be cause for many complaints
and FUD about epoll in general.

I recommend sticking to EPOLLONESHOT mostly, and EPOLLET for
unidirectional cases.

  * EPOLLONESHOT - easiest for bidirectional sockets,
    hard to get wrong once you use it

  * EPOLLET - Use it for listen sockets, pipes and FIFOs.
    That is, one-way stuff that's always EPOLLIN or EPOLLOUT-only,
    but can never be BOTH EPOLLIN or EPOLLOUT.  Theoretically it
    could be faster than EPOLLONESHOT for bidirectional sockets
    due to fewer syscalls, but tricky-to-use as it depends on client
    traffic patterns (which clients can abuse).

Fwiw: I've read and understood fs/eventpoll.c in the Linux source;
it's fairly self-contained and should be easy-to-understand to
anybody remotely familiar with C.  There's a lot hate on epoll out there
and I strongly suspect the default (level-trigger) behavior is to blame.

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