Re: concurrent access to multiple local git repos is error prone

From: Alexander Mills <alexander.d.mills@gmail.com>
Date: Aug 6, 2018, 07:36 UTC
Message-ID: <CA+KyZp760a3yTF6ghiNh=c5FoU36MN3cdQU5J8NF2Ss+nwRqyQ@mail.gmail.com>
In-Reply-To: <20180805081116.GG44140@aiede.svl.corp.google.com>

Hi Johnathan,

Yeah this concurrency problem is real. Not only does it happen with `git status` the same thing happens with `git rev-parse --show-toplevel`. What happens is that I get no stdout when repos are accessed concurrently (and no stderr). If I limit concurrency to 1, the problem goes away. When I up the concurrency, the problem is sporadic, which is the exact signal for a concurrency/race-condition related issue. The signs are damn clear. I have seen this problem on MacOS I think a year back on a different project, but I never reported it b/c I hadn't really verified it.

Like I said I am on Ubuntu. I have 3 git repos that are incorporated into the tool that's generating the problem. For one repo I got this:

$ git fsck

Checking object directories: 100% (256/256), done. dangling tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904

For `$ git version --build-options` I have:

git version 2.17.1 cpu: x86_64 no commit associated with this build sizeof-long: 8

-alex

On Sun, Aug 5, 2018 at 1:11 AM, Jonathan Nieder <jrnieder@gmail.com> wrote:

Show 25 quoted lines

> Alexander Mills wrote:
>
>> Yeah in this case what appeared to be happening is that if `git status` was
>> called concurrently, frequently I wouldnt get any stdout..
>
> Thanks for reporting.  A few questions:
>
> What platform are you on?  What version of Git are you running?  What
> is the output of "git version --build-options"?
>
> What is the exit status from these "git status" invocations that
> didn't write output?  What options are you passing to "git status"?
> Are there any other interesting symptoms?
>
> Is this part of a larger tool or script?  Are there other operations
> going on (e.g. something sending signals to these git processes)?
>
> Does the repository pass "git fsck"?  Any other symptoms or hints that
> could help in tracking this down?
>
> Can you paste a transcript of the commands or script you ran and what
> output it produced?  Is this something I should be able to reproduce?
>
> Thanks and hope that helps,
> Jonathan

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Alexander D. Mills
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