Resume() call directly inside desc's callback is safe in current implementation. Should remove that note from the comment.

[zhuyie]

in the epoll/kqueue implementation, when callback invoked, no locks been held. looks like it's safe to call Resume() in callback.

but the following comment made me confused.

    // Start adds desc to the observation list.
    //
    // Note that if desc was configured with OneShot event, then poller will
    // remove it from its observation list. If you will be interested in
    // receiving events after the callback, call Resume(desc).
    //
    // Note that Resume() call directly inside desc's callback could cause
    // deadlock.
    //
    // Note that multiple calls with same desc will produce unexpected
    // behavior.
    Start(*Desc, CallbackFn) error