Race condition handling

[rtrv]

I've been investigating problems with flashes and figured out that redis-session-store doesn`t provide any handling of concurrent session changes. The problem is overviewed well here: https://paulbutcher.com/2007/05/01/race-conditions-in-rails-sessions-and-how-to-fix-them/
The solution from this article is outdated.
We use redis-session-store and we like it, but in case we have a lot of AJAX there are some problems. I think, if it's a common issue, I could work on improving this gem using concepts from outdated solution. There is no problem without concurrents requests, so such behaviour could be optional for gem user.

[vovanmozg]

This is still a problem today