Linux epoll() implementation

x::epoll is a reference, and x::epollptr is a nullable pointer reference to a reference-counted object that implements the Linux kernel epoll(7) API.

class myEpollCallbackObj : public x::epoll::callbackObj {
    void event(const fd &fileDesc,
               event_t events);

x::ref<myEpollCallbackObj> cb(x::ref<myEpollCallbackObj>::create());

x::epoll epollSet(x::epoll::create());

x::fd myFd(netaddr("", "smtp")->connect();

myFd->epoll(EPOLLIN, epollSet, cb);

A file descriptor object's epoll() method adds the file descriptor to the epoll set, and attaches a callback object to the file descriptor. An epoll object's epoll_wait waits for an event to occur in the event set, after which the event() method from the file descriptor's associated callback object gets invoked, with parameters indicating which file descriptor's event has occured, and what the event is.