class SearchWorker extends Worker {
    public function run() {}
}

class Search extends Thread {
    public $data;

    public function __construct($data)
    {
        $this->data = $data;
    }

    public function run()
    {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_URL, 'http://httpbin.org/get?search='.$this->data->s);
        $this->data->r = curl_exec($ch);
        curl_close($ch);
    }
}

$pool = new Pool(4, 'SearchWorker');
$data = [];
$search = array('cats','dogs','cows','cars','trucks','booze','bottles','furniture','metal','elements');

foreach ($search as $i => $s) {
    $dataN = new Threaded();
    $dataN->i = $i;
    $dataN->s = $s;
    $data[] = $dataN;
    $pool->submit(new Search($dataN));
}

while ($pool->collect());

$pool->shutdown();

class SearchWorker extends Worker {
    private $ch;

    public function __construct()
    {
        $this->ch = curl_init();
        curl_setopt($this->ch, CURLOPT_RETURNTRANSFER, TRUE);
    }

    public function run() {}
}

class Search extends Thread {
    public $data;

    public function __construct($data)
    {
        $this->data = $data;
    }

    public function run()
    {
        curl_setopt($this->worker->ch, CURLOPT_URL, 'http://httpbin.org/get?search='.$this->data->s);
        $output = curl_exec($this->worker->ch);
        $this->data->r = $output;
    }
}