gpxlogger (x: ✘3.23 is near. Please test!)

[Fred Wright]

On Mon, 26 Jul 2021, Gary E. Miller wrote:

> I want to get gpsd 3.23 shipped, due to issue #144.
>
> Please test git head.  Unless a show-stopper bug pops up, I'd like
> to get 3.23 shipped by Aug 2.  Version 3.22 was shipped Jan 8, 2021.

I haven't done any multi-platform testing yet, but I did find that 
gpxlogger has become unquittable, due to a863161f8.

Previously, quit_handler() was doing things which were technically illegal 
but worked, including a gps_close() which terminated the gps_mainloop(). 
The new code seems to assume that gps_mainloop() returns frequently, which 
it doesn't, since it's designed to iterate internally, and the only reason 
for the outer loop was for reconnecting.  Adding the sig_flag check 
there doesn't help, because it's never reached.

The real problem is the bad design of gps_mainloop(), which provides no 
way to stop its iterations other than by error or timeout.  Aside from the 
whole signal handler issue, relying on something like gps_close() to stop 
it is ugly and probably not thread-safe.  The obvious fix is to have the 
hook function return a value which indicates whether iterations should 
continue, perhaps with a different return value from gps_mainloop() itself 
to distinguish "stop iteration" from "error".  However, this would change 
the API.  Currently, the only use of gps_mainloop() within the project is 
in gpxlogger, though it's not known whether users are using it.  And 
testing the return value of a function declared void would lead to flaky 
behavior.  The conservative thing to do would be to introduce a new 
version of gps_mainloop() under a different name, and keep the broken one 
(probably a wrapper around the good one) around for a while for 
compatibility.

Or a cheap fix for the impending release might be just to revert a863161f8 
(at least the portion that applies to gpxlogger), and fix it properly 
later.  Or skip the logging and have the signal handler call _exit() the 
way gpsctl is now doing.

Fred Wright