Re: [libgpiod][PATCH 3/7] tests: event: extend test coverage for reading multiple line events at once

[Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>]

czw., 19 gru 2019 o 14:35 Kent Gibson <warthog618@xxxxxxxxx> napisał(a):
>
> > +
> > +     ret = gpiod_line_request_both_edges_events(line, GPIOD_TEST_CONSUMER);
> > +     g_assert_cmpint(ret, ==, 0);
> > +
> > +     gpiod_test_chip_set_pull(0, 4, 1);
> > +     usleep(10000);
> > +     gpiod_test_chip_set_pull(0, 4, 0);
> > +     usleep(10000);
> > +     gpiod_test_chip_set_pull(0, 4, 1);
> > +     usleep(10000);
> > +
>
> I assume the sleep is to wait for the event to be generated from the
> call gpiod_test_chip_set_pull, which is not guaranteed to occur before
> the call returns, otherwise you can toggle the line too fast and may
> miss events.

Yes, this is why I put it there. Otherwise, some simulated interrupts
were being dropped when they fired while the previous ones were still
served.

> Arbitrary sleeps in code, including tests, should be avoided as they
> are brittle and obsure what you are actually waiting for.

Indeed.

> An alternative in this case is to add a second event fd and wait for
> the event to arrive there before continuing.
>

I'm not sure I understand. We can't have two event fd's for the same
line. Or are you thinking about setting up a second line, generating
events on it and consuming them so that we can rely on the timing to
make sure the events were registered for the first one too?

Bart