dest.c: Use monotonic time for cups_enum_dest

[zdohnal]

Patch written by Adam Williamson.

gettimeofday() is vulnerable to clock jumps, so it is better to use clock_gettime() to avoid issues with libcups if system changes clock, f.e. in Live CDs.

[michaelrsweet]

I'm thinking we need a CUPS API that returns a monotonic value, probably a double for portability.

double cupsGetClock(void);

If we back-port this to CUPS 2.4.x, we'll want to leave this as private API (_cupsGetClock).

[michaelrsweet]

[master 0350eba] Add cupsGetClock API.

Also in libcups repository.

[zdohnal]

@michaelrsweet hmm, looks like Mac monotonic clock precision is buggy...

I've looked into Mac results on current master branch and there is something wrong with MacOS test suite - I see fail for cupsGetClock(), but the CI run shows as passed:

cupsGetClock(initial): PASS (0)
cupsGetClock(1 second): PASS (1.09793)
cupsGetClock(5 seconds): FAIL (got 5.14539, expected 5.0 +/- 0.1)
cupsGetClock(10 seconds): FAIL (got 10.2297, expected 10.0 +/- 0.1)
cupsGetClock(30 seconds): FAIL (got 30.3457, expected 30.0 +/- 0.1)
cupsGetClock(60 seconds): FAIL (got 60.3833, expected 60.0 +/- 0.1)
cupsGetClock(120 seconds): FAIL (got 120.406, expected 120.0 +/- 0.1)

I will try the CLOCK_MONOTONIC_RAW, if it helps MacOS...

[zdohnal]

To no avail... here is the post I found about Mac and CLOCK_MONOTONIC https://discussions.apple.com/thread/253778121?page=2&sortBy=rank .