(PHP 5 >= 5.2.0, PHP 7, PECL swoole >= 1.9.0)
swoole_async_write — Write data to a file stream asynchronously
$filename
   , string $content
   [, integer $offset
   [, callable $callback
  ]] ) : bool
filenameThe filename being written.
contentThe content writing to the file.
offsetThe offset.
callback
   Returns TRUE on success or FALSE on failure.