Re: [PATCH 10/16] worktree: make branch creation distinct from worktree population

[Duy Nguyen <pclouds@gmail.com>]

(resend, +everybody)

On Sun, Jul 12, 2015 at 10:27 AM, Eric Sunshine <sunshine@sunshineco.com> wrote:
>>> So, if I understand your concern correctly, then you are worried that,
>>> following the git-branch invocation, ref_exists() could return the
>>> wrong answer with a pluggable ref-backend since it might be answering
>>> based upon stale information. Is that what you mean? If so, I can see
>>> how that it could be an issue. (As far as I can tell, the current
>>> file-based backend doesn't have a problem with this since it's hitting
>>> the filesystem directly to answer the ref_exists() question.)
>>
>> I meant for this final sentence to end like this:
>>
>>      ...to answer the ref_exists() question, but it still seems
>>      fragile since some future change could introduce caching.
>
> In this case, it's easy enough to side-step the issue since there's no
> need to call ref_exists() if the new branch was created successfully
> (since we know it exists). The logic would effectively become this:
>
>     branch = ...
>     if (create_new_branch) {
>         exec "git branch newbranch branch"
>         exec "git symbolic-ref HEAD newbranch"
>     } else if (ref_exists(branch) && !detach)
>         exec "git symbolic-ref HEAD branch"
>     else
>         exec "git update-ref HEAD $(git rev-parse branch)"
>     exec "git reset --hard"

Yeah.. Another option we can take is deal with this at run-command.c
level (and outside this series) because this could affect everywhere:
by default, invalidate all cache after running any git commands. The
caller can pass options to keep some cache intact if they know the
command won't touch it.

If ref_exists() is the only thing we use, right now it does not use
cache so we should be safe. If the new ref backend introduces a cache,
they would need to examine all callers anyway, including this one. The
cache in refs.c seems to be for for_each_ref.. only, which we don't
call here.
-- 
Duy