I would suggest in whatever environment/language you are in to just write a quick test where you spawn a bunch of threads writing and reading from the global, and see what happens.
Sorry no one actually answered your question, and just assumed your case would never happen.
I actually ran into this case recently, when trying to diagnose the impact of a bug in the wild (eg I can obviously fix it in a later release, but understanding the impact of the bug here was also very critical!)