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QBSERVE VS TIMING CODE

If Exception is thrown in certain EventHandler, all EventHandlers subscribed after that one will not be executed.

Call to certain EventHandler blocks the thread until all work in that EventHandler is completed.

That means that objects/values in earlier subscribed EventHandler are updated earlier then in other EventHandlers, which might have consequences to program logic.

EventHandlers are executed in sequence, one after another, in the order in which they are subscribed to the event.That has some not so obvious consequences: Subscribed EventHandlers are being invoked synchronously on a single thread.

A more popular way to write invocation of handlers today is: But, theoretically speaking, a “thread race” condition is possible, between time SubjectEvent is checked for null, and events are invoked, some other thread can remove handlers from the SubjectEvent, which would result in null reference exception. Let us mention that in (1), we used a method that is popular in literature. Change subject state and notify observers S.SubjectEvent += ( new Observer( " 3")).Update S.SubjectEvent += ( new Observer( " 2")).Update S.SubjectEvent += ( new Observer( " 1")).Update Public class EventArgsSubject : EventArgs ObserverState = ((ArgsSubject)args).SubjectState Ĭonsole.WriteLine( " Observer ", Public void RemoveObserver(IObserver observer) Public void AddObserver(IObserver observer) Protected List observersList = new List() Here is how Classic Observer, as described in GoF literature looks like. While in C#, Event keyword is already integrated, that is implementation of Observer pattern, one can still decide to roll-out one's own version/implementation.

In simple words, one component ( Subject) notifies other components ( Observers) that state changed. We say that Observer “subscribes” with Subject to get notified of Subject’s state change. Observer pattern, or sometimes called Subject-Observer pattern, defines a one-to-many dependency between objects, so that when one object ( Subject) changes its state, all its dependent objects ( Observers) are notified and updated.

QBSERVE VS TIMING CODE

The code presented is tutorial, demo-of-concept level and for brevity, does not handle or show all variants/problematic issues. Programmers often have illusion of parallelism, which is not reality, and is an important issue in today’s multi-core-processors world. The fact that Event mechanism in reality provides Synchronous calls is often overlooked and not emphasized enough. Modern usage of Observer pattern in C# is practically related to usage of Event mechanism and Classic Observe pattern is made obsolete in C#. Modern languages like C# have integrated Event mechanism, via which Observer pattern has practically been integrated into language mechanisms. We first present Classic Observer pattern which is one of GoF patterns and is often mentioned in literature. The intended audience are Intermediate C# programmers and above. This is a tutorial article on Observer pattern in C#.