[Asterisk-code-review] core: Use eventfd for alert pipes on Linux when possible (asterisk[13])

[Sean Bright]

Hello Mark Michelson, George Joseph, Jenkins2, Joshua Colp,

I'd like you to reexamine a change.  Please visit

    https://gerrit.asterisk.org/5497

to look at the new patch set (#5).

Change subject: core: Use eventfd for alert pipes on Linux when possible
......................................................................

core: Use eventfd for alert pipes on Linux when possible

The primary win of switching to eventfd when possible is that it only
uses a single file descriptor while pipe() will use two. This means for
each bridge channel we're reducing the number of required file
descriptors by 1, and - if you're using timerfd - we also now have 1
less file descriptor per Asterisk channel.

The API is not ideal (passing int arrays), but this is the cleanest
approach I could come up with to maintain API/ABI.

I've also removed what I believe to be an erroneous code block that
checked the non-blocking flag on the pipe ends for each read. If the
file descriptor is 'losing' its non-blocking mode, it is because of a
bug somewhere else in our code.

In my testing I haven't seen any measurable difference in performance.

Change-Id: Iff0fb1573e7f7a187d5211ddc60aa8f3da3edb1d
---
M configure
M configure.ac
A include/asterisk/alertpipe.h
M include/asterisk/autoconfig.h.in
M include/asterisk/channel.h
A main/alertpipe.c
M main/bridge_channel.c
M main/channel_internal_api.c
M main/utils.c
9 files changed, 412 insertions(+), 203 deletions(-)


  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/97/5497/5
-- 
To view, visit https://gerrit.asterisk.org/5497
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Iff0fb1573e7f7a187d5211ddc60aa8f3da3edb1d
Gerrit-PatchSet: 5
Gerrit-Project: asterisk
Gerrit-Branch: 13
Gerrit-Owner: Sean Bright <sean.bright at gmail.com>
Gerrit-Reviewer: George Joseph <gjoseph at digium.com>
Gerrit-Reviewer: Jenkins2
Gerrit-Reviewer: Joshua Colp <jcolp at digium.com>
Gerrit-Reviewer: Mark Michelson <mmichelson at digium.com>
Gerrit-Reviewer: Sean Bright <sean.bright at gmail.com>