File cache for Git HTTP GET /info/refs

We know that GET /info/refs is a very common request, and that it dynamically generates two types of response that only change when the repo is updated. There is great potential for caching here.

What is difficult about this is dealing with concurrent pushes, for instance this scenario:

push A reaches post-receive and kicks off git upload-pack --advertise-refs
push B reaches post-receive and kicks off git upload-pack --advertise-refs
advertise-refs from push B finishes and writes the cached response
advertise-refs from push A finishes and overwrites the cached response
result: push B is not visible in the cached GET /info/refs response

What is simplest way to prevent this problem?

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information