We have this nice function get_uptime() that shields the global variable `stats_n_seconds_working` from the rest of the Tor files. But then we undermine that by saying ``` extern long stats_n_seconds_working; ``` in main.h and we just start using that variable directly all over. There are a few lonely users of get_uptime(). We should move everybody over to using get_uptime, and get rid of the scary extern. (Also check out how we're *writing* to the extern variable, in hibernate.c. There's no way that could confuse anybody down the road!)