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Date: Tue, 17 Jun 2014 12:04:23 +0200
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Subject: Refactoring our IO multiplexing layer
From: jpauli@php.net (Julien Pauli)

Hey :-)

I spent few hours analyzing PHP's IO multiplexing parts.

IO multiplexing refers to calls to select() / poll() / epoll() or kqueue().

Simple notice : everything is sparse everywhere, we don't have an
IOmux layer designed.

I plan to write an RFC on the subject.
The goal is to centralize IO mux calls in a layer to be used
everywhere. My analyze leads to those points :

- FPM has something, but not designed to be shared
- User streams use hardcoded select() , with an ugly emulation for poll()
- We have nothing about epoll() or kqueue(), except in FPM
- curl_multi_select() uses hardcoded select()
- php_cli_server uses hardcoded select()
- mysqlnd uses hardcoded select() for its poll() mecanisms

Python already have a layer, at
http://hg.python.org/cpython/file/abcf17bc5eae/Modules/selectmodule.c

Apache's APR has a nice layer with adapters, at
https://github.com/apache/apr/blob/trunk/poll/unix/pollset.c

Still, there exist the excellent libevent http://libevent.org/

So basically, the first question will be do we need it ?
I would say yes. As we are talking about PHP6 and modernising our API,
it is time I think to implement IO mux correctly and don't use the old
select() everywhere where there is a better implementation (epoll and
kqueue are both faster, and they dont suffer from any FD_SETSIZE
limit)
Also, we didnt talk about things as websockets etc... yet, for PHP6 ,
but it is sure that nowadays 2014, IO mux is a must-have.

Second question will be : do we use, and then link against libevent
(or any other lib that could fit the need) , or do we develop our own
layer, based on the FPM layer which is pretty nicely done (just not
shareable elsewhere at the moment).

And then, will people be interested by the RFC ?

Thx,


Julien