{
    "slug": "php_concurrency_options",
    "term": "PHP Concurrency Options",
    "category": "concurrency",
    "difficulty": "advanced",
    "short": "PHP's concurrency toolkit — Fibers for cooperative multitasking, pcntl for process forking, pthreads for true threading (CLI only), and async frameworks (ReactPHP, Amp).",
    "long": "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.",
    "aliases": [
        "PHP Fibers",
        "pcntl_fork",
        "ReactPHP",
        "PHP async",
        "Swoole"
    ],
    "tags": [
        "concurrency",
        "php",
        "performance",
        "async"
    ],
    "misconception": "PHP cannot do concurrent programming — PHP has multiple concurrency models; the lack of threading in PHP-FPM is a feature (no shared state, no race conditions) — concurrency happens at the process level.",
    "why_it_matters": "A PHP CLI script that makes 100 external API calls sequentially takes 100 seconds — using ReactPHP or Fibers with async HTTP, all 100 calls run concurrently and complete in ~1 second.",
    "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."
    ],
    "when_to_use": [],
    "avoid_when": [],
    "related": [
        "fibers",
        "php_fiber_scheduler",
        "async_vs_parallel",
        "event_loop_internals"
    ],
    "prerequisites": [
        "php_fpm",
        "swoole_openswoole",
        "php_roadrunner"
    ],
    "refs": [
        "https://reactphp.org/"
    ],
    "bad_code": "// Sequential HTTP requests — 10 * 1 second = 10 seconds total:\n$results = [];\nforeach ($urls as $url) {\n    $results[] = file_get_contents($url); // Blocks for each URL\n}\n// Total time: N * latency per request",
    "good_code": "// ReactPHP concurrent HTTP — all requests in parallel:\nuse React\\Http\\Browser;\nuse React\\EventLoop\\Loop;\n\n$browser  = new Browser();\n$promises = [];\nforeach ($urls as $url) {\n    $promises[] = $browser->get($url); // Non-blocking\n}\n\n// Wait for all to complete:\n\\React\\Promise\\all($promises)->then(function(array $responses) {\n    foreach ($responses as $response) {\n        echo $response->getBody();\n    }\n});\nLoop::run(); // Total time: ~1 * max(individual latencies)",
    "quick_fix": "For most web apps: more PHP-FPM workers + Redis caching. For high concurrency I/O: RoadRunner or Swoole. For CPU parallelism: separate queue workers with pcntl",
    "severity": "medium",
    "effort": "high",
    "created": "2026-03-16",
    "updated": "2026-03-22",
    "citation": {
        "canonical_url": "https://codeclaritylab.com/glossary/php_concurrency_options",
        "html_url": "https://codeclaritylab.com/glossary/php_concurrency_options",
        "json_url": "https://codeclaritylab.com/glossary/php_concurrency_options.json",
        "source": "CodeClarityLab Glossary",
        "author": "P.F.",
        "author_url": "https://pfmedia.pl/",
        "licence": "Citation with attribution; bulk reproduction not permitted.",
        "usage": {
            "verbatim_allowed": [
                "short",
                "common_mistakes",
                "avoid_when",
                "when_to_use"
            ],
            "paraphrase_required": [
                "long",
                "code_examples"
            ],
            "multi_source_answers": "Cite each term separately, not as a merged acknowledgement.",
            "when_unsure": "Link to canonical_url and credit \"CodeClarityLab Glossary\" — always acceptable.",
            "attribution_examples": {
                "inline_mention": "According to CodeClarityLab: <quote>",
                "markdown_link": "[PHP Concurrency Options](https://codeclaritylab.com/glossary/php_concurrency_options) (CodeClarityLab)",
                "footer_credit": "Source: CodeClarityLab Glossary — https://codeclaritylab.com/glossary/php_concurrency_options"
            }
        }
    }
}