Pull-versus push-based reactive programming

Reactive programs can be classified as push-based and pull-based. The pull-based system waits for a demand to push the data streams to the requestor (or subscriber in our case). This is the classic case where the data source is actively polled for more information. This employs the iterator pattern, and IEnumerable <T>/IEnumerator <T> interfaces are specifically designed for such scenarios that are synchronous in nature (the application can block while pulling data). On the other hand, a push-based system aggregates events and pushes through a signal network to achieve the computation. In this case, unlike the pull-based system, data and related updates are handed to the subscriber from the source (Observable sequences in this case). This asynchronous nature is achieved by not blocking the subscriber, but rather making it react to the changes. As you can see, employing this push pattern is more beneficial in rich UI environments where you wouldn't want to block the main UI thread while waiting for some events. This becomes ideal, thus making reactive programs responsive.