[Bug 670864] New: [gstdatetime] now and utc_now unit tests sometimes fail

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=670864
  GStreamer | gstreamer (core) | git

           Summary: [gstdatetime] now and utc_now unit tests sometimes
                    fail
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: davidsf at axis.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=208470)
 View: https://bugzilla.gnome.org/attachment.cgi?id=208470
 Review: https://bugzilla.gnome.org/review?bug=670864&attachment=208470

Use g_get_current_time and try twice

To reproduce the bug, I run the GstDateTime unit tests test_GstDateTime_now and
test_GstDateTime_utc_now, "forever":

GST_CHECKS=test_GstDateTime_now,test_GstDateTime_utc_now make -C tests/check
gst/gstdatetime.forever

Within 10 seconds, I get a failure like the following:

Running suite(s): GstDateTime
50%: Checks: 2, Failures: 1, Errors: 0
gst/gstdatetime.c:52:F:general:test_GstDateTime_now:0:
'gst_date_time_get_second (dt)' (45) is not equal to 'tm.tm_sec' (44)

I've attached a proposed patch for this bug. The tests use the Linux system
call time() for getting a time reference, and then call the tested functions
gst_date_time_new_now_local_time and gst_date_time_new_now_utc. The tests
expect to get times within the same second. We've found that there are two
things that can cause the failure:

1) The Linux system call time() and g_get_current_time don't always return a
time with the same second component, even if they are called simultaneously.
2) Between two calls that ask what time it is, some time may pass and we might
simply get different seconds for that reason.

Regarding 1), I've changed from using time() to using g_get_current_time in the
tests. g_get_current_time is used by the tested functions, and itself uses the
system call gettimeofday. Some measurements showed that, on my system, time()
switched over to a new seconds about 2-3 milliseconds later than gettimeofday.
I.e., when I got the second 45 from gettimeofday, I could call time() many
times during about 2-3 milliseconds, and still get 44. This may have to do with
the different granularities of time() and gettimeofday.

Regarding 2), I added a while loop that tries twice if the tests get different
seconds.

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