CVS commit: src/tests/lib/libpthread

["Robert Elz" <kre%netbsd.org@localhost>]

Module Name:    src
Committed By:   kre
Date:           Sun Dec 11 10:02:53 UTC 2022

Modified Files:
        src/tests/lib/libpthread: t_condwait.c

Log Message:
This test makes (made) a false assumption about the way that
process scheduling works.   That a process (or in this case,
a thread) is no longer blocked at time T does not mean that it
will resume execution at time T.   The OS is free to devote
resources to other processes/threads instead - all we should
normally be able to expect is that if it is not unblocked before
time T, that it will not start running before then.

In general though, the pthread_cond_*wait() functions don't guarantee
even that - but for this test, the possibility of something else
randomly signalling the condvar isn't believable, so don't worry about
that possibility (but do fail without calling strerror(0) on the off
chance it does happen).

Once we cease testing that the process resumed running before some
particular time, we can stop dealing with qemu timekeeping issues,
it might (seem to) take qemu twice as long as was requested before
the thread resumes, but that's OK - the same thing could happen on
a loaded system for other reasons.

Beyond that, the test also has (had) a race condition.   When using
CLOCK_REALTIME though that clock needed to have advanced to T before
the ETIMEDOUT should happen, there is no guarantee that it will stay >T
(CLOCK_REALTIME is allowed to be reset backwards).   So, only test
that the current time (after ETIMEDOUT) >= T when we're using
CLOCK_MONOTONIC - for CLOCK_REALTIME the time might have stepped
back between when the ETIMEDOUT happened and when the thread
obtains the current clock reading.  For that case, all we can test
is that the ETIMEDOUT actually happens.

With much of what was there now gone, the code can be simplified,
we no longer need to do timespec arithmetic, just one comparison
(simpler to test that Tend >= Tstart+period than Tend-Tstart > period
as we need Tstart+period for the abstime value for the timeout anyway).

Note that this still tests for the issue reported in PR lib/47703
which is where the test came from in the first place.

ps: we seem to be missing pthread_cond_clockwait() which is the same
as pthread_cond_timedwait() except that the clock to use is passed
as a parameter, rather than as an attribute of the condition variable.


To generate a diff of this commit:
cvs rdiff -u -r1.9 -r1.10 src/tests/lib/libpthread/t_condwait.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.