(PHP 5 >= 5.2.0, PHP 7, PECL swoole >= 1.9.0)
swoole_async_writefile — Write data to a file asynchronously
$filename
   , string $content
   [, callable $callback
   [, int $flags = 0
  ]] ) : bool
filenameThe filename being written.
contentThe content writing to the file.
callback
flags
   Returns TRUE on success or FALSE on failure.