Polling standard input with selectors

[showermat]

I need to wait for a keypress or signal, and thought the easiest way to do this would be to use poll and friends. In the simplified example below, the program responds properly when ^C is pressed, but an assertion not (pkey.ident == 0) fails when input is provided on standard input. It looks like the selectors module uses 0 to mean that the slot is empty, when 0 also happens to be the file descriptor of stdin. Is this intentional? Is there a workaround or better way to achieve this?

import selectors, posix, os
var events = newSelector[int]()
events.registerHandle(0, {Read}, 0)
events.registerSignal(2, 0)
for event in events.select(-1): echo($event & "\n")

(As accessory questions, where is it documented that I need to import posix and os in order to use selectors (see #7667), and what type should I replace int with in the example above to indicate that I don't want to pass any application-defined data at all?)

[dom96]

Have you considered modifying the selectors module to use a different number to signify emptiness? Negative numbers typically signify errors but maybe that's all we've got. We can also use Option[T] but that might affect the runtime too much.

As accessory questions, where is it documented that I need to import posix and os in order to use selectors (see #7667)

I've noticed this too, and I think it's a Nim bug.

[davidnorthetal]

This clearly needs to be fixed, but one workaround (in some cases) would be to use dup - it's in the posix-module as well.

[showermat]

That's a good workaround! For now, I'm just opening and reading /dev/tty, because that also solves another problem I was having. But I verified that replacing 0 with -1 in a few places in ioselectors_epoll.nim seems to fix it. @dom96 Should I open a pull request?