class type pollset =object..end
method find : Unix.file_descr -> Netsys_posix.poll_req_eventsNot_found if the descriptor is not in the set.method add : Unix.file_descr -> Netsys_posix.poll_req_events -> unitmethod remove : Unix.file_descr -> unitmethod wait : float ->
       (Unix.file_descr * Netsys_posix.poll_req_events *
        Netsys_posix.poll_act_events)
       listwait
        is invoked.
There is no guarantee that the list is complete.
        It is unspecified how the set reacts on descriptors that became
        invalid (i.e. are closed) while being member of the set. The set
        implementation is free to silently disregard such descriptors,
        or to report them as invalid. It is strongly recommended to
        remove descriptors before closing them.
method dispose : unit -> unitcancel_wait the required OS resources are automatically allocated
        again. Only for cancel_wait it is ensured that the disposal
        remains in effect.method cancel_wait : bool -> unit
        When the bit is true, any wait invocation will immediately
        time out. It is allowed to set the cancel bit from another thread,
        and when it becomes true, a parallel running wait will
        see that and timeout. Note that there is no
        protection against race conditions: It is possible that wait
        returns events that are found at the same time the cancellation
        is carried out, i.e. you cannot rely on that the list returned
        by wait is empty.
        This is the only method of a pollset that is allowed to be called
        from a different thread. If not supported on a platform this method
        will fail.