parallel/docs/worker-pool.md

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Worker Pool	/worker-pool

The easiest way to use workers is through a worker pool. Pool implements Worker, so worker pools can be used to enqueue tasks in the same way as a worker, but rather than using a single worker process or thread, the pool uses multiple workers to execute tasks. This allows multiple tasks to be executed simultaneously.

Pool

The Pool interface extends Worker, adding methods to get information about the pool or pull a single Worker instance out of the pool. A pool uses multiple Worker instances to execute enqueued tasks.

<?php

namespace Amp\Parallel\Worker;

/**
 * An interface for worker pools.
 */
interface Pool extends Worker
{
    /** @var int The default maximum pool size. */
    const DEFAULT_MAX_SIZE = 32;

    /**
     * Gets a worker from the pool. The worker is marked as busy and will only be reused if the pool runs out of
     * idle workers. The worker will be automatically marked as idle once no references to the returned worker remain.
     *
     * @return \Amp\Parallel\Worker\Worker
     *
     * @throws \Amp\Parallel\Context\StatusError If the queue is not running.
     */
    public function getWorker(): Worker;

    /**
     * Gets the number of workers currently running in the pool.
     *
     * @return int The number of workers.
     */
    public function getWorkerCount(): int;

    /**
     * Gets the number of workers that are currently idle.
     *
     * @return int The number of idle workers.
     */
    public function getIdleWorkerCount(): int;

    /**
     * Gets the maximum number of workers the pool may spawn to handle concurrent tasks.
     *
     * @return int The maximum number of workers.
     */
    public function getMaxSize(): int;
}

If a set of tasks should be run within a single worker, use the Pool::getWorker() method to pull a single worker from the pool. The worker is automatically returned to the pool when the instance returned is destroyed.

Global worker pool

A global worker pool is available and can be set using the function Amp\Parallel\Worker\pool(?Pool $pool = null). Passing an instance of Pool will set the global pool to the given instance. Invoking the function without an instance will return the current global instance.