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27 april 2026 om 22:11:51 Dave Brown

Concurrency Patterns in PHP

PHP's traditional request-per-process model is simple but limiting. Modern PHP offers several concurrency approaches.

Fork-Based Parallelism

Using pcntl_fork(), a parent process creates child processes that inherit its full state via OS copy-on-write:

$futures = [];
foreach ($chunks as $chunk) {
    $futures[] = run(function () use ($chunk) {
        return processChunk($chunk);
    });
}

$results = array_map(fn ($f) => $f->value(), $futures);

Advantages: Full state inheritance, true parallelism, no serialization overhead for captured variables.

Challenges: Connection management (database, Redis, HTTP clients must be reset in child processes), memory overhead per process.

Async I/O

For I/O-bound workloads, async libraries like ReactPHP or AMPHP multiplex operations on a single thread:

$promises = [];
foreach ($urls as $url) {
    $promises[] = $httpClient->request('GET', $url);
}
$responses = await(all($promises));

Advantages: Low memory footprint, excellent for HTTP calls and database queries.

Challenges: Callback complexity, limited CPU parallelism, ecosystem compatibility.

Choosing the Right Model

| Workload | Best Approach | |----------|--------------| | CPU-bound computation | Fork (pcntl) | | Many HTTP API calls | Async I/O | | Mixed CPU + I/O | Fork with async per child | | Real-time streaming | Event loop (ReactPHP) |

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