Call-time pass-by-reference has been removed [duplicate]
Only call time pass-by-reference is removed. So change:
call_user_func($func, &$this, &$client ...
To this:
call_user_func($func, $this, $client ...
&$this should never be needed after PHP4 anyway period.
If you absolutely need $client to be passed by reference, update the function ($func) signature instead (function func(&$client) {)