试图加载类“”；线程“；来自全局命名空间.你忘了一个“；使用“；陈述

描述：

创建了一个扩展Thread的php类ChildThread。它看起来像这样：

use Thread;
class ChildThread extends Thread
{
    public $data;
    private $anonymous_func;
    public function __construct($anonymous_func)
    {
        $this->anonymous_func = $anonymous_func;
    }
    public function run(){
        $func = $this->anonymous_func;
        $this->data = $func();
    }
}

问题：

我得到以下错误：

尝试从全局命名空间加载类"Thread"。你是不是忘记"使用"语句了吗？

我显然有一个use语句，它使用了正确的类：

/**
 * When the start method of a Thread is invoked, the run method code will
 * be executed in separate Thread, asynchronously.<br/>After the run method
 * is executed the Thread will exit immediately, it will be joined with
 * the creating Thread at the approriate time.
 * @link http://www.php.net/manual/en/class.thread.php
 */
class Thread extends Threaded implements Traversable, Countable, ArrayAccess {
  /** class code here **/
}

问题：

为什么它说我需要一个"使用"语句，而我已经在使用它了？