Windows named pipes hits unreachable code during read operation

[agneil]

This is an issue we're having trouble reproducing, however, there have been instances of crashing on Windows due to the unreachable! line in the snippet of the read_done function below:

mio/src/sys/windows/named_pipe.rs

Lines 859 to 863 in 9bd0e95

	// Move from the `Pending` to `Ok` state.
	let mut io = me.io.lock().unwrap();
	let mut buf = match mem::replace(&mut io.read, State::None) {
	State::Pending(buf, _) => buf,
	_ => unreachable!(),

I don't see an apparent cause, but I'm curious as to whether it could be possible the snippet below inside scheduled_read is returning an error that causes mem::forget not to be run as anticipated so the state is Err rather than Pending?

mio/src/sys/windows/named_pipe.rs

Lines 705 to 709 in 9bd0e95

	let e = unsafe {
	let overlapped = me.read.as_ptr() as *mut _;
	let slice = slice::from_raw_parts_mut(buf.as_mut_ptr(), buf.capacity());
	me.read_overlapped(slice, overlapped)
	};

[Thomasdezeeuw]

@carllerche do you have time to look at this?

[Thomasdezeeuw]

@agneil any chance that #1772 solve this problem? The reporter of that issue is hitting the same panic as you did here.