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

[Andy Wingo]

Hi :)

On Tue 13 Jan 2015 13:58, address@hidden (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