Cancels the unit of work represented by this reference.
No events will be sent by a
Publisher until demand is
signaled via this method.
signals demand for the number of
onNext events that the
if positive, then the
Publisher is bound by contract to not send more than
this number of
onNext events and if negative, then this signals to the
Publisher that it may send an infinite number of events, until the subscription
gets cancelled or the stream is complete.