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

From: [email-masked] (Ludovic Courtès)
Date: Thu, 23 Jun 2016 15:09:22 +0200

Hello,

Andy Wingo <[email-masked]> skribis:

> 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.

Sounds like a plan.  There could be programs that will break if ‘sleep’
gives them an inexact instead of an integer.  Maybe we can assume this
is an unlikely situation, though.

Thoughts?

Ludo’.