Makes sense, and is probably the "safest" you can get. Since, as you say, you know exactly the state of everything on that thread when you're in your handler, you can also know that your thread local was set properly before the epoll_pwait() call.

It's probably code I'd want to isolate somewhere, with big warnings so any future reader understands why it is how it is, but I agree it's probably the safest way to do it.