(PHP 5 >= 5.2.0, PHP 7, PECL swoole >= 1.9.0)
swoole_async_readfile — Read a file asynchronously
filenameThe filename of the file being read.
callbackfilenameThe name of the file.
contentThe content readed from the file.
成功时返回 TRUE， 或者在失败时返回 FALSE。