A simple scratch script for testing parallel processes in PHP.

parallel-process.php

<?php

use Symfony\Component\Console\Output\ConsoleOutput;
use Symfony\Component\Process\Process;

require_once __DIR__ . '/../../vendor/autoload.php';

/*
 * Playing with using only Process to handle parallel processes
 * but still enabling each to stream their content at the same time.
 * Uses proc_open on under the hood and doesn't allow call backs. It
 * does cut down on needing to fork a process first.
 */
$output = new ConsoleOutput();

/** @var Process $processes */
$processes = [];

$processes[] = new Process('php /app/scripts/dummy.php 1');
$processes[] = new Process('php /app/scripts/dummy.php 2');
$processes[] = new Process('php /app/scripts/dummy.php 3');

/** @var Process $process */
foreach ($processes as $process) {
    $process->start();
}

// Output the data
foreach (streamProccessesOutput($processes) as $type => $data) {
    echo $data;
}

foreach ($processes as $process) {
    $process->wait();
}

// TODO: make this more performant
function streamProccessesOutput($processes)
{
    while (count($processes)) {
        /** @var Process $process */
        foreach ($processes as $key => $process) {
            $value = $process->getIterator()->current();

            if ($value) {
                yield $value;
            } elseif (!$process->isRunning()) {
                unset($processes[$key]);
            }
        }
    }
}