Add timeout to Base.prompt

[IanButterworth]

Adds an optional timeout to prompt to return the default after a given number of seconds

Edit: Tweaked to

julia> Base.prompt("Continue (y/n)?", default = "n", timeout = 3)
Continue (y/n)? [n] timeout 3 seconds: 
...
...
...
Continue (y/n)? [n] timeout 3 seconds: timed out 
"n"

May be useful for features such as #39026 where hanging indefinitely on user input, rather than erroring may be suboptimal

[IanButterworth]

I seem to be doing something illegal in the tests here by using redirect_stdin.

I just want to simulate prompt waiting on stdin for keypresses.

@test Base.prompt(IOButter(), buf, "baz", default="foobar", timeout = 1) == "foobar"

doesn't work because readline(IOBuffer()) returns empty immediately.

@test Base.prompt(stdin, buf, "baz", default="foobar", timeout = 1) == "foobar"

doesn't seem to work in the tests, perhaps because stdin reaches eof?

Is there another way to simulate an open stdin with no data?

[vtjnash]

throwto is an internal interface that may corrupt the task and stream state if used

[IanButterworth]

I see. So implementing this timeout would need to be done at a lower read* level?

[IanButterworth]

I thought about sending something to stdin to unblock readline. Is that possible? This approach doesn't work

function foo()
    Timer((t)->println(stdin), 1)
    readline(stdin)
end

[IanButterworth]

Another approach that doesn't work. Fake closing the stdin.
It just hangs. The readline only seems to query whether the stdin is open once

begin
    stat_before = stdin.status
    Timer((t)->stdin.status = Base.StatusClosed, 4)
    try
        line = readline(stdin)
    finally 
        stdin.status = stat_before
    end
end

[vtjnash]

Oh yeah, I forget there was a fake StatusEOF that can be triggered manually. It should be okay to grab the correct locks and set that:

    lock(stream.cond)
    stream.status = StatusEOF
    notify(stream.cond)
    unlock(stream.cond)

It is likely not well-tested or supported, since we don't implement half-open streams properly, but it does exist already at least.

[IanButterworth]

Nice! This works

julia> begin
           Timer(4) do t
               lock(stdin.cond)  
               stdin.status = Base.StatusEOF
               notify(stdin.cond)
               unlock(stdin.cond)
           end
           readline(stdin)
       end
""

julia>

[IanButterworth]

@vtjnash Tests are finally passing. I took the lead from what other stdin tests do.

I introduced this as a second method to maintain the non-timeout method for IJulia etc.
And I couldn't figure out how to provide the same functionality for IJulia's stdin handler, which opens a text input box and seems quite unusual

[IanButterworth]

Good to go @vtjnash ?

[IanButterworth]

Bump (this just came up on slack as a wanted feature)

[fredrikekre]

I think the "timeout 5 seconds" part looks a bit strange or misplaced. Does it have to be displayed to the user at all?

[aramirezreyes]

Seems useful to have but probably a clearer wording like "Proceed? y/n. Default value [n] will be used in 5 seconds: y" would be better?

[JeffBezanson]

This looks like a good feature but I'm iffy on the implementation. It would be much better not to define this only for LibuvStream, since if input is redirected you'll get a MethodError. It's also not great to poke at the LibuvStream internals. So I think this should wait until we have a reliable way to implement it.

[JeffBezanson]

Good point from @vtjnash : arguably the timeout should be canceled as soon as you start typing.

[JeffBezanson]

In that case, it's possible this can only really work for a TTY, and for other IO streams just ignore the timeout?