IAsyncEnumerable and throttling-CodePudding

Is it possible to throttle the data when consuming IAsyncEnumerable<T>? I have a stream of data coming in rapidly, and I'm only interested in the last element every N seconds.

Thanks.

CodePudding user response：

It would seem to make sense to have a different endpoint which returns the most recent event rather than a dealing with the stream.

If you have to deal with a queue/stream you could consume the events and assign each new incoming one to something like latest and read that at the desired interval.

CodePudding user response：

One solution is to convert IAsyncEnumerable<T> to IObservable<T> and leverage power of System.Reactive

First, you need a converter. I couldn't find builtin so I've created my own

using System;
using System.Collections.Generic;
using System.Reactive.Subjects;

public class AsyncEnumerableToObservable<T> : IObservable<T>
{
    private readonly IAsyncEnumerable<T> _source;
    private readonly Subject<T> _subject = new();

    public AsyncEnumerableToObservable(IAsyncEnumerable<T> source)
    {
        _source = source;
        BeginConsume();
    }

    public IDisposable Subscribe(IObserver<T> observer) => _subject.Subscribe(observer);

    private async void BeginConsume()
    {
        try
        {
            await foreach (var item in _source)
            {
                _subject.OnNext(item);
            }

            _subject.OnCompleted();
        }
        catch (Exception e)
        {
            _subject.OnError(e);
        }
    }
}

public static class AsyncEnumerableExtensions
{
    public static IObservable<T> ToObservable<T>(this IAsyncEnumerable<T> source)
    {
        return new AsyncEnumerableToObservable<T>(source);
    }
}

With this converter you can use myEnumerable.ToObservable() and use Sample method for throttling from System.Reactive

static class Program
{
    static async Task Main(string[] args)
    {
        IAsyncEnumerable<int> seq = CreateSeq();
        seq.ToObservable().Sample(TimeSpan.FromSeconds(1)).Subscribe(Console.WriteLine);

        await Task.Delay(TimeSpan.FromSeconds(10));
    }

    private static async IAsyncEnumerable<int> CreateSeq()
    {
        int i = 0;
        while (true)
        {
            await Task.Yield();
            i  ;
            yield return i;
        }
    }
}