bug#21804: 25.0.50; file-notify-tests failure on Cygwin

[Michael Albinus]

Ken Brown <kbrown@cornell.edu> writes:

> Hi Michael,

Hi Ken,

> I've made some progress on understanding why some file notifications
> aren't triggered in the tests on Cygwin.  One issue is that
> file-notify--test-read-event-timeout has to be increased drastically
> in order for `created' and `changed' events to be received.  These can
> take 5 seconds or more.

Well, gfilenotify uses a native library like inotify or kqueue when
available. If not, it does polling.

I guess the latter happens in the cygwin case. Maybe we need to
determine the polling interval, and to set
file-notify--test-read-event-timeout larger than that. Will check,
whether information this could be retrieved from gfilenotify.

> A second issue is that a small delay is needed between the creation of
> a file watch and the beginning of file activity.  This is not normally
> a problem in interactive sessions.

I see. I will check further, whether I could modify Fgfile_add_watch
such a way that it returns only when it is able to create events.

> The attached patch takes care of both timing issues.  With this patch,
> all the inexpensive file-notify tests pass on all my Cygwin systems.

LGTM, please install.

I would also like to modify the expensive tests accordingly. Do you know
where I could retrieve a compiled Emacs 26 for cygwin?

> Best regards,
>
> Ken

Best regards, Michael.