A nonblocking test whether a connection has completed, or errored out
function mysql_async_connect_completed( resource $link_identifier = NULL, ): bool;
resource $link_identifier = NULL- The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If no connection is found or established, an E_WARNING level error is generated.
bool- - Has the connection finished (either successfully or with error).