Program.cs

using System.Reactive.Linq;

namespace Generation;

class Program
{
    static void Main()
    {
    }

    public static void GenerateItems()
    {
        IObservable<int> src = Observable.Generate(
            (Current: 0, Total: 0, Random: new Random()),
            state => state.Total <= 10000,
            state =>
            {
                int value = state.Random.Next(1000);
                return (value, state.Total + value, state.Random);
            },
            state => state.Current);
    }

    public static void GenerateTimedItems()
    {
        IObservable<int> src = Observable.Generate(
            (Current: 0, Total: 0, Random: new Random()),
            state => state.Total < 10000,
            state =>
            {
                int value = state.Random.Next(1000);
                return (value, state.Total + value, state.Random);
            },
            state => state.Current,
            state => TimeSpan.FromMilliseconds(state.Random.Next(1000)));
    }
}