Implementing observer pattern using WCF

Question

When I first posted this question I had strong coupling between my web service and application controller where the controller needed to open multiple threads to the service and

Answer 1

Not sure if this solution fits your particular task, but anyway:

1. Add paging parameters to your WS API (int pageNumber, int pageSize, out int totalPages)
2. Add a short-living TTL cache that associates request details (maybe a hash value) with output data

When your application asks for the first page, return it as soon as it's ready and put the whole bunch of collected/merged data to cache so when the next page is required you may use what is already prepared.

But note that you won't get the most up-to-date data, configure cache reloading interval cautiously.