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CSharp · Console

/Program.cs

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Reactive;
using System.Reactive.Linq;
using System.Runtime.ExceptionServices;

public class Program
{
    public static void Main()
    {
        var xs = CreateObservableEx<Unit>(async (o, ct) =>
        {
            await Task.Delay(10, ct);
            o.OnError(new Exception());
        }).Replay().RefCount();

        xs.Subscribe(x => Console.WriteLine(x));
        xs.Subscribe(x => Console.WriteLine(x), ex => Console.WriteLine(ex.Message));
        xs.DefaultIfEmpty().Wait();
    }

    public static IObservable<TSource> CreateObservableEx<TSource>(
        Func<IObserver<TSource>, CancellationToken, Task> subscribe)
    {
        return Observable.Create<TSource>(async (observer, cancellationToken) =>
        {
            Action<Exception> propagateError = (Exception error) =>
            {
                try { observer.OnError(error); }
                catch (Exception ex)
                {
                    ThreadPool.QueueUserWorkItem(_ => ExceptionDispatchInfo.Capture(ex).Throw());
                }
            };

			var innerObserver = Observer.Create<TSource>(observer.OnNext,
                propagateError, observer.OnCompleted);

            try { await subscribe(innerObserver, cancellationToken); }
            catch (Exception ex)
            {
                propagateError(ex);
            }
        });
    }
}