如何在php中异步调用函数

我想在用户单击按钮时执行这些函数，但我想在后台异步执行$model->user->email ? $model->sendUserMail(): "";，而其他函数将在单击发生时执行这是我的代码

if (isset($_POST['create_send'])) {
    if ($model->save()) {
        $model->order_id = strtotime(date("Y-m-d H:i:s")) + '' + $model->id;
        // send mail
        $model->sendMail();
        //send sms
        $messages = $model->sendSMSMessage($model);
        // create booking history
        $model->createBookingHistory($model , $messages);                     
        $model->user->email ? $model->sendUserMail(): "";
        if($model->booking_stage != 'inprogress'){
            $this->sendPushToSeller($model);
        }
        $model->update();
        $this->redirect(array('index', 'id' => $model->id));
    }
}