onCompleted

OnCompleted is a term used in various programming contexts to denote that a process, sequence, or stream has finished, and no further data will be produced. The precise meaning and usage depend on the framework.

In Reactive Extensions (Rx), OnCompleted is one of the three methods defined by the observer interface, along with OnNext and OnError. When the producer finishes emitting values, it calls OnCompleted on its observers, signaling that the observable sequence has completed. After OnCompleted is invoked, observers should not expect further OnNext or OnError calls, and it typically marks the end of the data stream where resources can be released or finalization performed.

In web applications built with ASP.NET Core, HttpResponse.OnCompleted registers a callback to run after the HTTP response has been fully written and flushed to the client. The callback (often asynchronous) is used for cleanup, logging, or releasing resources that should occur only after the response completes. The timing is post-response, and the callback is invoked regardless of the request’s outcome.

The term is not universal and may appear as a private method or naming convention in other contexts. Its common thread is the indication of a terminal or final event, contrasting with OnNext (data emission) and OnError (an error condition) in the Rx model.

See also: IObserver<T>, IObservable<T>, Reactive Extensions, HttpResponse.OnCompleted.