PHP Concurrency Options

Also Known As

TL;DR

Explanation

PHP concurrency options: (1) Fibers (PHP 8.1) — cooperative multitasking within a single thread, enables async/await patterns; (2) pcntl_fork() — true process forking for CPU-bound parallel work, each fork has its own memory; (3) parallel extension — true threads with shared memory (CLI only, experimental); (4) ReactPHP / Amp / Swoole — event loop frameworks that manage non-blocking I/O over Fibers or traditional callbacks; (5) PHP-FPM multiple workers — the standard PHP concurrency model — each request in a separate worker process. True parallelism in PHP requires multiple processes or Swoole's coroutines.

Common Misconception

Why It Matters

Common Mistakes

• Fibers for CPU-bound work — Fibers are cooperative concurrency for I/O, not parallel CPU execution.
• pcntl_fork() in web requests — forking in FPM creates orphan processes and database connection issues.
• Not handling child process exit in pcntl_fork() — zombie processes accumulate.
• Using Swoole without testing all dependencies for coroutine compatibility.

Code Examples

// Sequential HTTP requests — 10 * 1 second = 10 seconds total:
$results = [];
foreach ($urls as $url) {
    $results[] = file_get_contents($url); // Blocks for each URL
}
// Total time: N * latency per request

// ReactPHP concurrent HTTP — all requests in parallel:
use React\Http\Browser;
use React\EventLoop\Loop;

$browser  = new Browser();
$promises = [];
foreach ($urls as $url) {
    $promises[] = $browser->get($url); // Non-blocking
}

// Wait for all to complete:
\React\Promise\all($promises)->then(function(array $responses) {
    foreach ($responses as $response) {
        echo $response->getBody();
    }
});
Loop::run(); // Total time: ~1 * max(individual latencies)

References

• ↗ https://reactphp.org/

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