[staabm]

inspired by AI driven work in PHPStan-src, I realized that the pcntl extension has a pcntl_exec feature which allows to override the current process (instead of starting a sub-process and bridging signals, output back into the main process).

while this does not make things faster in my testing, I can see it saves memory

➜  xdebug-handler git:(pcntl_exec) ✗ hyperfine 'php test.php' --runs=5
Benchmark 1: php test.php (5 runs)
                mean     ±       σ          min     …     max
  Wall Time    3.255 s   ±   0.009 s      3.247 s   …   3.266 s
  Memory        28.4 MiB ±     0.1 MiB     28.3 MiB …    28.4 MiB
 

➜  xdebug-handler git:(main) ✗ hyperfine 'php test.php' --runs=5         
Benchmark 1: php test.php (10 runs)
                mean     ±       σ          min     …     max
  Wall Time    3.254 s   ±   0.010 s      3.243 s   …   3.269 s
  Memory        29.6 MiB ±     0.1 MiB     29.4 MiB …    29.8 MiB 

when running my super-simplified test.php:

<?php

use Composer\XdebugHandler\XdebugHandler;

require_once __DIR__ . '/vendor/autoload.php';

var_dump(extension_loaded('xdebug'));
echo "booting a second...\n";
sleep(1);

$xdebug = new XdebugHandler('myapp');
$xdebug->check();
unset($xdebug);

var_dump(extension_loaded('xdebug'));
echo "running a second...\n";
sleep(1);

I guess perf numbers might be different in case xdebug-handler needs to bridge a lot of data between the subprocess and the parent process. but I was not yet able to proof that with examples.

---

env:

➜  xdebug-handler git:(main) ✗ php -v                                   
PHP 8.5.11 (cli) (built: Sep 22 2026 13:32:06) (NTS)
Copyright (c) The PHP Group
Built by Homebrew
Zend Engine v4.5.11, Copyright (c) Zend Technologies
    with Xdebug v3.5.3, Copyright (c) 2002-2026, by Derick Rethans
    with Zend OPcache v8.5.11, Copyright (c), by Zend Technologies

➜  composer git:(main) php bin/composer diagnose                
Composer version: 2.11.999-dev+source
Checking Composer and its dependencies for vulnerabilities: OK
PHP version: 7.2.5 - Package overridden via config.platform, actual: 8.5.11
PHP binary path: /opt/homebrew/Cellar/php/8.5.11_1/bin/php
OpenSSL version: OpenSSL 4.0.3 29 Sep 2026
curl version: 8.23.0 libz 1.2.12 brotli brotli/1.2.0 zstd supported ssl OpenSSL/4.0.3 HTTP 1.0, 1.1, 2, 3
zip: extension present, unzip present, 7-Zip not available
Active plugins: 
Checking composer.json: OK
Checking composer.lock: OK
Checking platform settings: OK
Checking git settings: OK git version 2.56.0
Checking http connectivity to packagist: OK
Checking https connectivity to packagist: OK
Checking github.com oauth access: OK does not expire
Checking disk free space: OK

---

we are using this technique in phpstan-src 2.2.10 and 2.3.1 releases and it seems todo quite well. we do not yet have long term experience with it though.

this PR is mostly meant to get a discussion going and test this approach more widely and in more use-cases