From: Junio C Hamano <gitster@pobox.com>
Date: Fri, 23 Feb 2018 19:33:38 GMT
Subject: Re: [PATCH v4 08/13] commit-graph: implement --delete-expired
Message-ID: <xmqqo9kftsa5.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <67871288-ea70-69d4-9c3d-5cc946d8dbe2@gmail.com>

Derrick Stolee <stolee@gmail.com> writes:

> The (unlikely, but possible) race condition involves two processes (P1
> and P2):
>
> 1. P1 reads from graph-latest to see commit graph file F1.
> 2. P2 updates graph-latest to point to F2 and deletes F1.
> 3. P1 tries to read F1 and fails.
>
> I could explicitly mention this condition in the message, or we can
> just let P2 fail by deleting all files other than the one referenced
> by 'graph-latest'. Thoughts?

The established way we do this is not to have -latest pointer, I
would think, and instead, make -latest be the actual thing.  That is
how $GIT_DIR/index is updated, for example, by first writing into a
temporary file and then moving it to the final destination.  Is
there a reason why the same pattern cannot be used?