ReactiveCocoa/ReactiveCocoa — pull request #348 by jspahrsummers (2013-02-22 23:04:56+00:00)
Title: Fix thread safety of -[RACSignal concat:]

I noticed while browsing the code the other day that the `concattedDisposable` variable isn't accessed in a thread-safe manner.

It actually probably works fine on x86 because pointer-sized values are atomic, but ARM (iOS) could run into a race condition here.