DocumentationThreadPool::__construct()

ThreadPool::__construct() ​

(PHP 8.6+, True Async 1.0)

php
public ThreadPool::__construct(
    int $workers = 0,
    int $queueSize = 0,
    ?\Closure $bootloader = null,
    bool $coroutine = false,
    int $concurrency = 0,
)

Creates a new thread pool and starts all worker threads immediately. Workers remain alive for the lifetime of the pool, eliminating per-task thread-startup overhead.

Parameters ​

ParameterTypeDescription
$workersintNumber of worker threads. 0 (default) — autodetect via Async\available_parallelism().
$queueSizeintMaximum length of the pending task queue. 0 (default) means workers × 4. When the queue is full, submit() suspends the calling coroutine until a slot becomes available.
$bootloader?\ClosureWorker startup initialisation. The closure is deep-copied once and runs in every worker before the main task loop. Useful for autoload, connection-pool warmup, opcache pre-compile. If the bootloader throws, the entire pool is considered failed.
$coroutineboolWhen true, every task runs as a coroutine in its own child scope nested inside the worker's shared pool scope. Inside the task you can await, use channels, do I/O, and spawn — all without blocking the OS thread.
$concurrencyintConcurrency limit of coroutines inside a single worker. Used only when coroutine: true. 0 (default) — unlimited.

Exceptions ​

Throws \ValueError if $workers < 0 or $queueSize < 0.

Examples ​

Example #1 Basic pool creation ​

php
<?php

use Async\ThreadPool;
use function Async\spawn;
use function Async\await;

spawn(function() {
    // 4 worker threads, default queue size — 16
    $pool = new ThreadPool(workers: 4);

    $future = $pool->submit(fn() => 'hello from worker');
    echo await($future), "\n"; // hello from worker

    $pool->close();
});

Example #2 Explicit queue size ​

php
<?php

use Async\ThreadPool;
use function Async\spawn;

spawn(function() {
    // 4 workers, queue capped at 64 pending tasks
    $pool = new ThreadPool(workers: 4, queueSize: 64);

    // ... submit tasks ...

    $pool->close();
});

Example #3 Bootloader — worker startup initialisation ​

php
<?php

use Async\ThreadPool;
use function Async\spawn;

spawn(function () {
    $pool = new ThreadPool(
        workers: 4,
        bootloader: function () {
            require __DIR__ . '/vendor/autoload.php';
            App\Container::boot();
            App\Database::warmupPool(min: 4, max: 16);
        },
    );

    // ... submitted tasks see a fully initialised environment ...

    $pool->close();
});

Example #4 Coroutine mode — await inside a task ​

php
<?php

use Async\ThreadPool;
use function Async\spawn;
use function Async\await;

spawn(function () {
    $pool = new ThreadPool(workers: 4, coroutine: true);

    $future = $pool->submit(function () {
        // a regular blocking call correctly parks the coroutine
        // rather than blocking the worker's OS thread
        $pdo  = new PDO('mysql:host=localhost;dbname=app', 'user', 'pass');
        $rows = $pdo->query('SELECT * FROM users LIMIT 10')->fetchAll();
        return $rows;
    });

    print_r(await($future));
    $pool->close();
});

Example #5 Autodetect worker count from available CPUs ​

php
<?php

use Async\ThreadPool;

// workers: 0 (default) → Async\available_parallelism()
$pool = new ThreadPool();   // honours the container's cgroup quota / affinity

See Also ​