PHP Pthreads。 ＆＃34;没有找到类螺纹＆＃34;

Question

我是PHP的多线程初学者，使用pthreads。我尝试运行一些演示代码来理解基础知识。 所以，我已经安装了pthreads：

# php -m | grep pthreads
pthreads

# php -v
PHP 5.4.45 (cli) (built: Sep 25 2015 08:01:30)

我想运行几个连接到DB并进行查询的线程，但是使用一个共享的mysqli对象。我运行这段代码：

<?php

class SQLWorker extends Worker {

    public function __construct($hostname, $username, $password, $database, $port = 3306) {
        $this->hostname = $hostname;
        $this->username = $username;
        $this->password = $password;
        $this->database = $database;
    }

    public function run() {
        /* the static class scope acts as a kind of thread local storage for this class */
        self::$connection = new MySQLi
        ($this->hostname, $this->username, $this->password, $this->port);
    }

    public function getConnection() {
        return self::$connection;
    }

    protected $hostname;
    protected $username;
    protected $password;
    protected $database;
    protected $port;

    protected static $connection;
}

class SQLTask extends Threaded {
    public function __construct($sql) {
        $this->sql = $sql;
    }

    public function run() {
        /* fetch static (thread local) connection */
        $link = $this->worker->getConnection();

        if ($link) {
            /* execute query, keep result in local scope */
            $result = $link->query($this->sql);

            /* build up results as normal array */
            while (($row = $result->fetch_assoc())) {
                $rows[] = $row;
            }
        }

        /* store results in a fetchable form */
        $this->rows = $rows;
    }

    public function getResults() {
        return $this->rows;
    }
}

$pool = new Pool(4,
    SQLWorker::connection,
    ["localhost", "username", "password", "database"]);

$pool->submit(
    $task = new SQLTask("SELECT 1"));

$pool->shutdown();

/* you have your normal array of data here */
var_dump($task->getResults());

得到错误：

PHP Fatal error:  Class 'Threaded' not found in pThreads.php on line 31

我的问题在哪里？