Re: [PATCH 2/3] t/lib-httpd: make http-429 first-request check atomic

[Junio C Hamano <gitster@pobox.com>]

"Michael Montalbo via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Michael Montalbo <mmontalbo@gmail.com>
>
> http-429.sh records "already returned 429 once" with a "test -f"
> followed by a "touch" of a shared state file. That check-then-act is not
> atomic: Apache can run this CGI for several requests at once, and two of
> them can both pass the "test -f" before either "touch"es, so both treat
> themselves as the first request. The retry flow that drives this
> endpoint is mostly sequential, so this has not been seen to fail, but
> the race is latent.

OK.  And use of mkdir for atomicity is an obvious solution for such
a situtation.

> -if test -f "$state_file"
> +if test "$retry_after" != permanent && ! mkdir "$state" 2>/dev/null
>  then
>  	# Already returned 429 once, forward to git-http-backend
>  	# Set PATH_INFO to just the repo path (without retry-after value)
> @@ -52,9 +55,6 @@ then
>  	exec "$GIT_EXEC_PATH/git-http-backend"
>  fi
>  
> -# Mark that we've returned 429
> -touch "$state_file"
> -