using System;

using System.Linq;

using System.Collections.Generic;

using System.Threading.Tasks;

​

public class Program

{

    public static async Task Main()

    {

        var tasks = new List<Task<string>>{

            Task.Run( async () => { await Task.Delay(TimeSpan.FromSeconds(1.3)); return "Task1"; }),

            Task.Run( async () => { await Task.Delay(TimeSpan.FromSeconds(2.3)); return "Task2"; }),

            Task.Run( async () => { await Task.Delay(TimeSpan.FromSeconds(4.0)); return "Task3"; }),

            Task.Run( async () => { await Task.Delay(TimeSpan.FromSeconds(1.5)); throw new InvalidOperationException("Oooopsie"); return "Task4";}),

            Task.Run( async () => { await Task.Delay(TimeSpan.FromSeconds(3.1)); return "Task5"; })

        };

        await foreach( var task in WhenEach(tasks) )

        {

            try

            {

                Console.WriteLine(await task);

            }

            catch(Exception e)

            {

                Console.WriteLine(e.Message);

            }

        }

        Console.WriteLine("DONE");

    }

    public static async IAsyncEnumerable<Task<T>> WhenEach<T>(IEnumerable<Task<T>> tasks)

    {

        var taskList = new List<Task<T>>(tasks);

        while( taskList.Any() )

        {

            var task = await Task.WhenAny(taskList);

            taskList.Remove(task);

            yield return task;

        }

    }

}