Trying to setup communication by means of STDIO

master.php

<?php

function start_worker($id)
{
    printf("starting worker: %s\n", $id);
    $proc = proc_open(
        'php worker.php ' . $id,
        array(
            array('pipe', 'r'),
            array('pipe', 'w'),
            array('file', '/dev/null', 'w'),
        ),
        $pipes
    );

    return array($proc, $pipes);
}

function stop_worker($proc, array $pipes)
{
    fclose($pipes[0]);
    fclose($pipes[1]);
    fclose($pipes[2]);
    proc_close($proc);
}

function get_workers($count)
{
    $workers = array();
    for ($i = 1; $i <= $count; $i++) {
        $workers[$i] = start_worker($i);
    }
    return $workers;
}

$workers = get_workers(4);
$tasks = range(1, 10);

$working = array();
$write_pool = array();
$read_pool = array();
foreach ($workers as $id => $worker) {
    list(,$pipes) = $worker;
    $write_pool[$id] = $pipes[0];
    $read_pool[$id] = $pipes[1];
}

while ($tasks || $working) {

    $read  = array_intersect_key($read_pool, $working);
    $write = array_diff_key($write_pool, $working);
    $except = null;

    $ready = stream_select($read, $write, $except, 1);
    if (!$ready) {
        break;
    }

    while ($write && $tasks) {
        $stream = array_shift($write);
        $task   = array_shift($tasks);
        fwrite($stream, $task . PHP_EOL);
        $id = array_search($stream, $write_pool);
        printf("delegated task: %s to %s\n", $task, $id);
        $working[$id]= true;
    }

    while ($read) {
        $stream = array_shift($read);
        $result = fgets($stream);
        $result = rtrim($result, PHP_EOL);
        printf("got response: %s\n", $result);
        $id = array_search($stream, $read_pool);
        unset($working[$id]);
    }
}

worker.php

<?php

if ($_SERVER['argc'] > 1) {
    $id = $_SERVER['argv'][1];
} else {
    $id = 'unknown';
}

$fp = fopen('php://stdin', 'r');
while (!feof($fp) && ($s = fgets($fp)) !== false) {
    $s = rtrim($s, PHP_EOL);
    $d = mt_rand(0, 1000000);
    usleep($d);
    $c = sprintf(
        '%s (worker: %s, slept %d μs)' . PHP_EOL,
        strrev($s),
        $id,
        $d
    );
    echo $c;
}
fclose($fp);