Add per thread/test setup hook?

[seberg]

I was trying to use pytest-run-parallel for lowlevel CUDA code. In that context it happens that we need a per-thread setup (i.e. cuInit)

Doing that for almost every test as a decorator isn't nice, so one would use a fixture in pytest, but in pytest-run-parallel this isn't feasible.

I guess in an ideal world, one would have a setup_thread() hook that:

• Runs before the barrier.
• Knows the fixtures and *args, *kwargs probably. And can even replace them (i.e. per-thread context).

Or even something like a fixture(scope="thread") but I don't think that is possible :).

Right now, I can solve this (minus the barrier) by creating my own little pytest plugin that does the per-thread init, this isn't terribly difficult. It just leaves the nagging feeling that maybe it would be better to have a hook here.

[ngoldbaum]

I guess in an ideal world, one would have a setup_thread()

Seems reasonable for me to add that here. Not sure what the most natural way to do that in a plugin like this is. Maybe needs per-project configuration or a
conftest.py hook?

Or even something like a fixture(scope="thread") but I don't think that is possible

That probably needs to happen in pytest itself. Also seems reasonable to me though.

[seberg]

conftest.py hook?

That seems like the most approachable/easy thing to me, yeah. I had initially thought in the direction of something more towards fixture(scope="thread") and shelved the thought because I didn't see exactly what.

But, a simple hook that could also host the implementation of the tmpdir/tmp_path/thread_idx overrides, seems straight forward.
In principle, it might be neat to know the fixtures that are implicitly set as well, but it seems less important if it isn't easy.

EDIT: I realized that adding the hook at collection time might also be neat, then one could return a setup function if certain fixtures are used.

def _tmpdir_setup(item, *args, **kwargs):
    tmpdir = kwargs["tmpdir"] / threading.threadid()  # something like this
    kwargs["tmpdir"] = tmpdir
    return args, kwargs  # not sure we need args, as I am not sure they can be fixtures

@pytest.hookimpl("parallel-thread-setup")
def prallel_setup_func(item):
    if "tmpdir" in item.fixturenames:
        return _tmpdir_setup

Either just the first (as a hook) or second function would do (my use-case looks like the second, but I don't think it is needed in practice).

The second would be much like my existing mini plugin, but be a bit more obvious and have the advantage of running before the barrier, which is nice.