PHP线程似乎不起作用

Question

我在Promise中创建JavaScript，我决定使用线程。所以，我有以下课程：

class Promise extends Thread {

    protected $action = null;
    protected $then = null;
    protected $catch = null;

    public function __construct(callable $callback){
        $this->action = $callback;
        $this->start();
    }

    public function run(){
        call_user_func_array($this->action, [
            function($result){
                if($this->then !== null){
                    call_user_func($this->then, $result);
                }
            },
            function($result){
                if($this->catch !== null){
                    call_user_func($this->catch, $result);
                }
            }
        ]);
    }

    public function then(callable $callback){
        $this->then = $callback;
        return $this;
    }

    public function catch(callable $callback){
        $this->catch = $callback;
        return $this;
    }

}

然后我运行以下代码来测试它：

// Run the first thread
(new Promise(function($resolve, $reject){
    sleep(5);
    $resolve(true);
}))->then(function(){
    echo 'Resolved 5 second promise' . PHP_EOL;
});

// Run the second thread
(new Promise(function($resolve, $reject){
    sleep(2);
    $resolve(true);
}))->then(function($result){
    echo 'Resolved 2 second promise' . PHP_EOL;
});

// Show a status
echo 'Waiting for Promises\' to complete' . PHP_EOL;

运行时，我期待以下输出：

  

等待承诺'完成
  解决了2秒承诺   解决了5秒承诺

我得到以下输出：

  

解决了5秒承诺   解决了2秒承诺   等待Promises'完成

那么，为什么它不像时尚一样在线程中运行呢？

修改

我注意到，如果我将Promise分配给变量，它会正确输出，但我觉得我不应该这样做......