A server push model for client/server communications. The push architecture operates on top of a non-push (e.g., request/response) protocol (e.g., HTTP) to combine notifications from multiple data sources (e.g., email, text messaging, etc.). The server can be a middle-tier server (or proxy) to which a single web client registers interest in one or more notification types from one or more data sources. The mid-tier server aggregates the notifications from the various data sources and delivers the notifications to the requesting client via a single “push” pipe. The web client then distributes each notification to the appropriate parts of the client user interface. A producer/consumer locking mechanism eliminates blocking threads waiting on a mutual exclusion lock. A notification throttling mechanism distinguishes different types of notifications in order to guarantee that the client is not overloaded with too much information.