(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.
没有返回值。