Even if you fix the pid reuse problem, you'll still have difficulties parsing things like /proc/PID/maps. Unless your pseudo-file consists of fixed-size records - and as I recall, /proc/PID/maps doesn't, as each line has a variable-width path in it - your best option is just to read the entire file in at once, and fingers crossed it ended up being atomic (Obviously the system can't block operations that affect the maps file...)

signalfd gets this bit right.

It didn't take much POSIX programming before I started to look at Windows in a whole new light...