Re: kern/55663 (Support for EVFILT_USER in kqueue(2))

[Ruslan Nikolaev <nruslan_devel%yahoo.com@localhost>]

Also just to add regarding pipe-based solutions, some applications 
decided to use EVFILT_USER instead. Looking on the Internet show the 
following results (since 2010): e.g. libevent:

Date: Fri, 17 Sep 2010 00:34:13 -0400
Subject: Replace pipe-based notification with EVFILT_USER where possible
Commit: 53a07fe2f95c360d060b9fd58dfcd929c2c1aac2

Sufficiently recent kqueue implementations have an EVFILT_USER filter
that we can use to wake up an event base from another thread.  When
it's supported, we now use this mechanism rather than our old
(pipe-based) mechanism.  This should save some time and complications
on newer OSX and freebsds.
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