If you only consider `getenv`/`setenv` there are indeed many solutions, but it's not that simple. You also need to consider `putenv` (not that nasty, you just need to treat it like initial environment, which means you can't use a single range check) and accessing the `environ` variable directly (nasty).

Your particular solution doesn't work because people expect `getenv` to be async-signal-safe, which means you shouldn't be allocating memory.

Hmm ... doing an incref-like operation during `getenv` for a previously `setenv`ed variable that hasn't yet been accessed in this thread would be fine ... clear those refs during calls we know indicate knowledge refreshes ...