PHP Shared Memory Model

This repository reproduces edge cases for the PHP runtime environments that are using the shared memory model. It uses an example Symfony project with single test controller.

Installation

Clone the content of this repository:

cd ~/Projects
git clone git@github.com:SerheyDolgushev/php-shared-memory-model.git
cd php-shared-memory-model

Swoole

If you are on macOS, please follow the next steps:

1. Install pcre2:

   brew install pcre2

2. Link pcre2 into PHP, in this example /opt/homebrew/opt/php@8.3 is the PHP path:

   ln -s /opt/homebrew/opt/pcre2/include/pcre2.h /opt/homebrew/opt/php@8.3/include/php/ext/pcre/

3. Install swool using via PECL:

   pecl install -o -D 'enable-sockets="yes" enable-swoole-curl="yes" enable-brotli="yes" enable-cares="no" enable-mysqlnd="no" enable-swoole-pgsql="no" with-swoole-odbc="no" with-swoole-oracle="no" enable-swoole-sqlite="no" enable-openssl="no"' swoole

4. Disable swoole extension by default by removing extension=swoole.so from /opt/homebrew/etc/php/8.3/php.ini

Otherwise, please follow Swoole Installation guide.

RoadRunner

If you are on macOS, the simplest way to install RoadRunner is using Homebrew

brew install roadrunner

Otherwise, please follow RoadRunner Installation guide.

FrankenPHP

Follow the official instructions to download Standalone Binary, and please save it to ~/frankenphp.

Problem

First of all, have a glance at TestController. It has the only testAction method that returns the date and increased value of the counter property.

Start local PHP server:

php -S 127.0.0.1:8000 public/index.php

And send a few requests to the TestController::testAction:

% curl http://127.0.0.1:8000/test
[2024-02-24T08:05:03+00:00] Counter: 1
% curl http://127.0.0.1:8000/test
[2024-02-24T08:05:07+00:00] Counter: 1
% curl http://127.0.0.1:8000/test
[2024-02-24T08:05:10+00:00] Counter: 1

As expected, each response returns 1. Nothing strange here.

Swoole

Try to perform the same steps by running the Swoole runtime:

APP_RUNTIME=Runtime\\Swoole\\Runtime php -d extension=swoole.so public/swoole.php

And sending the same test requests:

% curl http://127.0.0.1:8000/test
[2024-02-24T08:07:59+00:00] Counter: 1
% curl http://127.0.0.1:8000/test
[2024-02-24T08:08:02+00:00] Counter: 2
% curl http://127.0.0.1:8000/test
[2024-02-24T08:08:06+00:00] Counter: 3

In this case, each response returns the incremented value of the previous response. Which might be unexpected behavior.

RoadRunner

Let's reproduce the same test in RoadRunner runtime:

rr serve -c rr.yaml -o http.pool.num_workers=1

And the same test requests:

% curl http://127.0.0.1:8000/test
[2024-02-24T08:10:45+00:00] Counter: 1
% curl http://127.0.0.1:8000/test
[2024-02-24T08:10:49+00:00] Counter: 2
% curl http://127.0.0.1:8000/test
[2024-02-24T08:10:52+00:00] Counter: 3

And the results are similar to the Swoole ones.

FrankenPHP

Let's use FrankenPHP to test:

cd ./public
APP_RUNTIME=Runtime\\FrankenPhpSymfony\\Runtime ~/frankenphp php-server -l 127.0.0.1:8000 -w ./index.php,1

And again the same test requests:

% curl http://127.0.0.1:8000/test
[2024-03-01T08:35:40+00:00] Counter: 1
% curl http://127.0.0.1:8000/test
[2024-03-01T08:35:41+00:00] Counter: 2
% curl http://127.0.0.1:8000/test
[2024-03-01T08:35:42+00:00] Counter: 3

Root cause

The simplified explanation is that PHP runtime uses Shared-nothing architecture by running the garbage collector to clear the memory between the requests. So memory is cleared after the previous request is completed and before the next one starts. But Swoole and RoarRunner runtimes are using Shared memory model which gives it its power. In this case, the memory is shared between different requests handled by the same worker. Please note, single-worker configuration have been used for all runtimes to simplify showcasing the problem. You can find more details in RoarRunner documentation.