Prefer kqueue when on OSX >= v10.12.2

[jcmfernandes]

Description

This a regression I introduced in 2.5.5 (sorry!). I got my hands on a Mac to confirm it (and test this fix).

I'm also taking the chance to address #266 (comment) as given that we check for linux/io_uring.h in extconf.rb, and that header was only introduced in Linux 5.1, my change is safe. In fact, while libev was looking for Linux >= 4.14 to compile safely, the backend is only activated on systems with kernel >= 5.6.1.

Types of Changes

• Bug fix.

Testing

• I added tests for my changes.
• I tested my changes locally.
• I tested my changes in staging.
• I tested my changes in production.

[ioquatix]

Should I release v2.5.6 with these changes?

[jcmfernandes]

Thanks for the quick reply @ioquatix!

I don't fully grasp the performance impact of using poll instead of kqueue on OSX. But given that probably no one uses OSX in production, and therefore this only impacts development environments, IMHO it's not an urgent fix that requires a release. Proof is that no one reported it; I noticed it while reading the code.

At the same time, if releasing isn't much of an hassle, it becomes a "why not?".

I would love to get more information on #266 but it seems like the reporter went missing.

[ioquatix]

kqueue is the event driven notification system which has efficient registration. poll is just a slightly more generic interface than select but performance is comparable (bad).

[tarcieri]

The reason kqueue wasn't the default for macOS in the past was due to alleged bugs:

http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#OS_X_AND_DARWIN_BUGS

See also #125

[ioquatix]

Yeah, it's notoriously unreliable, and I'm not sure if that's still the case, but when I did enable it a year or so ago, I felt it was stable enough (all tests in async were passing).

[smridge]

I'm also taking the chance to address #266 (comment) as given that we check for linux/io_uring.h in extconf.rb, and that header was only introduced in Linux 5.1, my change is safe. In fact, while libev was looking for Linux >= 4.14 to compile safely, the backend is only activated on systems with kernel >= 5.6.1.

I can confirm this was resolved! Many thanks!