From 7d86108a203c332be780c588c7e600920fc2c324 Mon Sep 17 00:00:00 2001 From: Thomas de Zeeuw Date: Sun, 7 Nov 2021 11:53:32 +0100 Subject: [PATCH] Add section about raw fd to portability guidelines --- src/poll.rs | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/src/poll.rs b/src/poll.rs index 62e82cce4..2f5550e68 100644 --- a/src/poll.rs +++ b/src/poll.rs @@ -163,6 +163,30 @@ use std::{fmt, io}; /// /// [event sources]: ./event/trait.Source.html /// +/// ### Accessing raw fd/socket/handle +/// +/// Mio makes it possible for many types to be converted into a raw file +/// descriptor (fd, Unix), socket (Windows) or handle (Windows). This makes it +/// possible to support more operations on the type than Mio supports, for +/// example it makes [mio-aio] possible. However accessing the raw fd is not +/// without it's pitfalls. +/// +/// Specifically performing I/O operations outside of Mio on these types (via +/// the raw fd) has unspecified behaviour. It could cause no more events to be +/// generated for the type even though it returned `WouldBlock` (in an operation +/// directly accessing the fd). The behaviour is OS specific and Mio can only +/// guarantee cross-platform behaviour if it can control the I/O. +/// +/// [mio-aio]: https://github.com/asomers/mio-aio +/// +/// *The following is **not** guaranteed, just a description of the current +/// situation!* Mio is allowed to change the following without it being considered +/// a breaking change, don't depend on this, it's just here to inform the user. +/// Currently the kqueue and epoll implementation support direct I/O operations +/// on the fd without Mio's knowledge. Windows however needs **all** I/O +/// operations to go through Mio otherwise it is not able to update it's +/// internal state properly and won't generate events. +/// /// # Implementation notes /// /// `Poll` is backed by the selector provided by the operating system.