Probably, $arg argument should be declared as mixed $arg = NULL, like it is in other methods. Its is useless to be just a string, since we want to pass more complex structures (array or object) and do so.
(PECL event >= 1.2.6-beta)
EventBufferEvent::setCallbacks — Assigns read, write and event(status) callbacks
$readcb
,$writecb
,$eventcb
,$arg
= ?Assigns read, write and event(status) callbacks.
readcb
Read event callback. See About buffer event callbacks .
writecb
Write event callback. See About buffer event callbacks .
eventcb
Status-change event callback. See About buffer event callbacks .
arg
A variable that will be passed to all the callbacks.
値を返しません。