Subject: Re: bug#19581: 'sleep' return value is incorrectly rounded

From: Andy Wingo <[email-masked]>
Date: Thu, 23 Jun 2016 11:02:45 +0200

Hi :)

On Tue 13 Jan 2015 13:58, [email-masked] (Ludovic Courtès) writes:

> I just noticed that ‘sleep’ essentially always rounds down its return
> value, which makes it unreliable, as in this example:
>
> $ time guile -c '(sigaction SIGINT +) (call-with-new-thread (lambda () (let loop () (kill (getpid) SIGINT) (loop)))) (let loop ((n 3)) (when (> n 0) (loop (sleep (pk "s" n)))))'
>
> ;;; ("s" 3)
>
> ;;; ("s" 2)
>
> ;;; ("s" 1)
>
> real	0m0.039s
> user	0m0.052s
> sys	0m0.017s
>
> Here ‘loop’ is meant to assure we sleep for roughly 3 seconds, but
> because of the incorrect rounding, we end up not sleeping at all.

Hummmmmmmmmm.

I don't think we can change anything in 2.0.  Right?

In master, how about (1) we allow sleep to take any real number, in
seconds; (2) sleep returns an inexact real number.  Then we can
deprecate usleep and "standardize" on sleeping in units of seconds.
Internally we refactor scm_std_usleep/* to take a 64-bit double for the
number of seconds to sleep and return a double for the time remaining.

WDYT?

Andy