Скачать или смотреть How to Count Live Concurrent Streams in C# with Reactive Extensions

Discover how to easily count the number of live, concurrent streams in C# using Reactive Extensions. Learn the implementation details in this step-by-step guide.
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This video is based on the question https://stackoverflow.com/q/62470259/ asked by the user 'James L' ( https://stackoverflow.com/u/2700/ ) and on the answer https://stackoverflow.com/a/62498146/ provided by the user 'Enigmativity' ( https://stackoverflow.com/u/259769/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Counting Live Concurrent Streams

If you're working with streams in C# , especially with the use of Reactive Extensions, you might encounter a situation where you need to track the number of active streams. Whether you're handling user events, network connections, or other asynchronous data feeds, knowing how many streams are currently live can be crucial for resource management and performance monitoring.

In this post, we'll explore a common question: How can you transform a stream of multiple inner streams into a live count of those that are currently active, i.e., not completed or errored?

To illustrate, we have a basic setup where we define a source stream from which we want to derive a count of active inner streams:

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Let’s break down the solution step-by-step.

Implementing CountLiveStreams

To create the CountLiveStreams function, we will leverage some powerful operators provided by Reactive Extensions. Below is the implementation that achieves this:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Implementation

Extension Method: We define CountLiveStreams as an extension method for IObservable<IObservable<T>>. This allows us to call it directly on any observable of observables.

SelectMany Operator: This operator flattens the streams from the source. It allows us to handle the inner streams as they emit items.

Materializing Streams: The Materialize() function transforms notifications into a more manageable format. Each notification is packaged, enabling us to examine the type of notification emitted (like Next, Completed, and Error).

Filtering Notifications: With .Where(x => x.Kind != NotificationKind.OnNext), we filter out the Next notifications because we are only interested in completed streams or those through which an error has been emitted.

Counting Streams: We use the expressions Select(x => -1) and StartWith(1) to count active streams. Each time a stream completes or errors out, we decrement the count by one (as indicated by -1), while the StartWith(1) denotes that at least one stream is considered active initially.

Running Tally: The .Scan((x, y) => x + y) operator takes the emissions from the previous step and maintains a running total, allowing us to see how many streams are live at any moment.

Conclusion

By implementing the CountLiveStreams method, you can seamlessly track the number of concurrent streams that are currently active in your application. This can significantly help you manage your resources effectively and ensure that your application can handle varying loads.

We hope this step-by-step guide helps you implement real-time stream counting in your C# applications efficiently! Happy coding!