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Subject: Re: Absolute timeouts and clock adjustments
To: Sebastian Huber <sebastian.huber@embedded-brains.de>,
 FreeBSD <freebsd-hackers@freebsd.org>
References: <58AD5802.30908@embedded-brains.de>
From: Eric van Gyzen <vangyzen@FreeBSD.org>
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Date: Tue, 14 Mar 2017 14:17:53 -0500
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On 02/22/2017 03:21, Sebastian Huber wrote:
> Hello,
>
> I try to figure out how the timeout mechanisms work in current FreeBSD.
> My interpretation (which could be completely wrong) of POSIX is
> something like this should happen:
>
> now 2017-02-22
> sem_timedwait(s, 2023-12-13)
> external entity adjusts time to 2050-01-01
> timeout of sem_timedwait() occurs due to the time adjustment
>
> Inside the kernel all absolute timeouts seem to use the uptime.

[...]

> The abs_timeout_gethz() returns the interval length in ticks of
> [abstime->cur, abstime->end]. Since the msleep() uses the uptime, does
> this mean that timeouts trigger not immediately due to time adjustments
> in FreeBSD?

I just fixed this in 12-CURRENT.  I'll merge it back to 11-STABLE in a 
few weeks.

Eric