Repl delays, background CPU

General
1

I've noticed some REPL issues. User perceptible delay and 100%CPU usage (two different issues). See below:

In emacs / racket-mode:

racket-mode> (let loop () (define form (read)) (unless (eq? form 'q) (println form) (loop)))

hello
*****delay*****
'hello
q

In DrRacket:

drracket>  (let loop () (define form (read)) (unless (eq? form 'q) (println form) (loop)))
hello
*****delay*****
'hello
q

On the command line:

[acarrico@russet terms]$ racket 
Welcome to Racket v8.13 [cs].
> (let loop () (define form (read)) (unless (eq? form 'q) (println form) (loop))
)
hello
*****FAST, no delay*****
'hello
hello
'hello
hello
'hello
hello
'hello
q
> 
***laptop fan goes on, .racket-wrapped uses 100% CPU in top****

Anyone else have similar issues? I'm on NixOS.

2

I got a chance to run my test on a Debian machine, also with Racket v8.13:

racket-mode: racket-mode repl under Debian seems responsive.

DrRacket: I replicate the delay issue under Debian

command line: I replicate the command line CPU 100% issue under Debian.

Maybe I'll open an issue since I've seen it on two machines.

3

This may be related (but I have no idea why DrRacket would be affected)

4

Yes. That is one of the issues, also this report:

Concurrent infinite loops and odd behavior from `read` in REPLs · Issue #4612 · racket/racket · GitHub

5

This seems to be a real thing, so discussion has moved to issue #4612.