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Long Polling in .NET: Efficient Polling Techniques

May 10, 2024 | .NET

In this article, we will delve into the concept of long polling in .NET, a more efficient alternative to traditional polling for near-real-time updates. We will explore the implementation of long polling in .NET, its advantages over regular polling, and the caveats to consider when using this technique.

The Benefits of Long Polling

Increasing Efficiency with Long Polling

Long polling optimizes the polling process by keeping the connection open until there is an update or a timeout occurs. This reduces the number of unnecessary requests and responses, making the communication more efficient.

// Sample long polling implementation in .NET
app.MapGet("/", async (CancellationToken userCt, ItemService itemService) =>
{
    var cts = CancellationTokenSource.CreateLinkedTokenSource(userCt);
    cts.CancelAfter(TimeSpan.FromSeconds(30));

    while (!cts.IsCancellationRequested)
    {
        if (itemService.AnyNewItems())
        {
            return Results.Ok(itemService.GetNewItem());
        }

        // Delay for responsiveness without decreasing performance
        await Task.Delay(50);
    }

    return Results.NoContent();
});

In this code snippet, we can see a basic implementation of long polling in .NET. By utilizing a cancellation token and a timeout mechanism, the server efficiently waits for updates before responding to the client.

Implementing More Efficient Long Polling

To further enhance the efficiency of long polling, we can leverage techniques such as using a Task Completion Source in a Singleton service for persistent data. This approach eliminates the need for continuous checks and improves the scalability of the application.

// Advanced long polling implementation in .NET
app.MapGet("/", async (CancellationToken userCt, ItemService itemService) =>
{
    var cts = CancellationTokenSource.CreateLinkedTokenSource(userCt);
    cts.CancelAfter(TimeSpan.FromSeconds(30));

    var timeoutTask = Task.Delay(-1, cts.Token);
    var itemArrivedTask = itemService.WaitForNewItem();

    var completedTask = await Task.WhenAny(itemArrivedTask, timeoutTask);

    if (completedTask == itemArrivedTask)
    {
        var item = await itemArrivedTask;
        itemService.Reset();
        return Results.Ok(item);
    }

    return Results.NoContent();
});

By utilizing a more sophisticated long polling implementation, we can optimize resource utilization and ensure a more responsive communication process between the client and server.

Caveats of Long Polling

Considerations for High-Frequency Updates

Long polling may not be suitable for scenarios with extremely frequent updates, as it can lead to performance issues and negate the benefits of this technique. It is essential to evaluate the update frequency before opting for long polling.

Browser Connection Limitations

Modern browsers impose restrictions on the number of active connections per domain, which can impact the effectiveness of long polling. Developers should be mindful of these limitations and implement strategies to mitigate potential bottlenecks.

Resource Consumption Concerns

The resource consumption of the server should be taken into account when implementing long polling. Depending on the server’s capabilities, it may be more efficient to handle frequent short-lived connections rather than fewer long-lived connections.

Conclusion

In conclusion, long polling in .NET offers a more efficient mechanism for obtaining near-real-time updates compared to traditional polling. By implementing long polling techniques effectively, developers can optimize resource utilization and enhance the responsiveness of their applications. Stay tuned for future articles where we explore other communication patterns such as Server-Sent Events and WebSockets. Remember, SignalR uses Long Polling as a fallback option, showcasing its importance in the realm of backend communication strategies.

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