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From: "Alejandro R. Mosteo" <alejandro@mosteo.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT corrupted builds with below second changes
Date: Thu, 15 Mar 2018 14:24:10 +0100
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Date: 2018-03-15T14:24:10+01:00
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On 14/03/18 23:56, Randy Brukardt wrote:
> "Alejandro R. Mosteo" <alejandro@mosteo.com> wrote in message
> news:p8atvh$74r$1@dont-email.me...
>> Hi,
>>
>> I'm doing some automated testing that involves very fast file generation
>> and recompilation. Platform is linux, GPL 2017 or FSF 7.2. I've observed
>> that gprbuild seems to not detect that a file is changed if less than a
>> second has elapsed. I will guess here that the timestamp being used has
>> second precision. This leads to supposedly up-to-date builds that aren't,
>> among other funny effects.
>>
>> I faintly remember having read about this somewhere, but I'm unable to
>> find anything related in web searches. Anyone has experienced this?
> 
> Not with GNAT, but we used to have such problems with Janus/Ada programs. I
> believe it caused certain ACATS tests to intermittently fail. I think I
> "fixed" that by introducing a delay into the compiler in certain
> circumstances (the delay being barely noticable to humans, but long enough
> to ensure that the time stamps are unique).

I did this initially but it mounted up, so I'm now manually deleting 
.o/.ali files for a few critical files only.

> [I don't remember for sure
> whether I fixed the problem, but since I don't remember it happening in the
> last 5 years, it seems likely that I did something to prevent it.] A better
> fix would have been to stop using time for such checks (compiles having
> gotten fast enough to make identical timestamps probable, and more so with
> every new generation of computers), but that would have required a lot of
> compiler and library change. (Definitely not the quick fix I was looking for
> at the time.)
> 
> It wouldn't surprise me if GNAT ran into similar issues -- the file
> timestamps on Windows (which is what we were/are using) have a 2 second
> granularity.
> 
>                                         Randy.

The funny thing is I'm almost sure of having read somewhere that this 
had been addressed in gnat specifically, but I can't locate it.

Thanks,
Álex.