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Re: [RFC PATCH 3/3] test-lib: add the '--stress' option to run a test repeatedly under load

On Tue, Dec 04, 2018 at 07:11:08PM +0100, Ævar Arnfjörð Bjarmason wrote:
> It's a frequent annoyance of mine in the test suite that I'm
> e.g. running t*.sh with some parallel "prove" in one screen, and then I
> run tABCD*.sh manually, and get unlucky because they use the same trash
> dir, and both tests go boom.
> You can fix that with --root, which is much of what this patch does. My
> one-liner for doing --stress has been something like:
>     perl -E 'say ++$_ while 1' | parallel --jobs=100% --halt-on-error soon,fail=1 './t0000-basic.sh --root=trash-{} -v'
> But it would be great if I didn't have to worry about that and could
> just run two concurrent:
>     ./t0000-basic.sh
> So I think we could just set some env variable where instead of having
> the predictable trash directory we have a $TRASHDIR.$N as this patch
> does, except we pick $N by locking some test-runs/tABCD.Nth file with
> flock() during the run.

Is 'flock' portable?  It doesn't appear so.

> Then a stress mode like this would just be:
>     GIT_TEST_FLOCKED_TRASH_DIRS=1 perl -E 'say ++$_ while 1' | parallel --jobs=100% --halt-on-error soon,fail=1 './t0000-basic.sh'

This doesn't address the issue of TCP ports for various daemons.

> And sure, we could ship a --stress option too, but it wouldn't be
> magical in any way, just another "spawn N in a loop" implementation, but
> you could also e.g. use GNU parallel to drive it, and without needing to

GNU 'parallel' may or may not be available on the platform, that's why
I stuck with the barebones shell-loops-in-the-background approach.

> decide to stress test in advance, since we'd either flock() the trash
> dir, or just mktemp(1)-it.

While 'mktemp' seems to be more portable than 'flock', it doesn't seem
to be portable enough; at least it's not in POSIX.

And in general I'd prefer deterministic trash directory names.  If I
re-run a failed test after fixing the bug, then currently the trash
directory will be overwritten, and that's good.  With 'mktemp's junk
in the trash direcory's name it won't be overwritten, and if my bugfix
doesn't work, then I'll start accumulating trash directories and won't
even know which one is from the last run.