poll.poll may return non readable events despite the only registered interest being for readables

[glandium]

Here is a reproducer:

use mio::windows::NamedPipe;
use mio::{Events, Interest, Poll, Token};
use std::env;
use std::os::windows::io::{FromRawHandle, IntoRawHandle};
use std::process::{Command, Stdio};

fn main() {
    if env::var("FOO").is_ok() {
        println!("Hello, world!");
    } else {
        let mut proc = Command::new(std::env::current_exe().unwrap())
            .env("FOO", "1")
            .stdout(Stdio::piped())
            .spawn()
            .unwrap();

        let mut out =
            unsafe { NamedPipe::from_raw_handle(proc.stdout.take().unwrap().into_raw_handle()) };

        let mut events = Events::with_capacity(16);
        let mut poll = Poll::new().unwrap();
        poll.registry()
            .register(&mut out, Token(0), Interest::READABLE)
            .unwrap();
        poll.poll(&mut events, None).unwrap();
        dbg!(events);
        proc.wait().unwrap();
    }
}

The dbg prints:

[src/main.rs:24:9] events = [
    Event {
        token: Token(
            0,
        ),
        readable: false,
        writable: true,
        error: false,
        read_closed: false,
        write_closed: fakse,
        priority: false
        aio: false,
        lio: false,
        details: event {
            flags: POLL_SEND,
            data: 0,
        },
    },
]

[Thomasdezeeuw]

Stdout isn't usually opened for reading, can you reproduce this on a handle/socket that can actually be used for reading?

Also the dbg! output contains fakse?

[glandium]

Stdout isn't usually opened for reading, can you reproduce this on a handle/socket that can actually be used for reading?

It's the stdout of the subprocess. So it is to be used for reading.
I've also now discovered that I'm also getting readable events when there's nothing more to read (read returns Ok(0)).

Also the dbg! output contains fakse?

I didn't copy/paste, so it's just a typo.

[Darksonn]

Isn't this just "spurious events are possible"?

I've also now discovered that I'm also getting readable events when there's nothing more to read (read returns Ok(0)).

Readable interest is used to signal that EOF has arrived, so that's normal.

[glandium]

I've also now discovered that I'm also getting readable events when there's nothing more to read (read returns Ok(0)).

Readable interest is used to signal that EOF has arrived, so that's normal.

Indefinitely? (repolling after getting Ok(0) still returns a readable event ; that only happens on Windows)

[Thomasdezeeuw]

I'm not sure, it could very well be a bug in Mio's NamedPipe code, but at the moment we don't really have a Windows expert to figure it out, we have some more issues in this area (https://github.com/tokio-rs/mio/issues?q=is%3Aissue+is%3Aopen+named+pipe), but no one to fix them :(