How to implement Task.WhenAny() with a predicate

Question

I want to execute several asynchronous tasks concurrently. Each task will run an HTTP request that can either complete successfully or throw an exception. I need to aw

Answer 1

Another way of doing this, very similar to Sir Rufo's answer, but using AsyncEnumerable and Ix.NET

Implement a little helper method to stream any task as soon as it's completed:

static IAsyncEnumerable> WhenCompleted(IEnumerable> source) =>
    AsyncEnumerable.Create(_ =>
    {
        var tasks = source.ToList();
        Task current = null;
        return AsyncEnumerator.Create(
            async () => tasks.Any() && tasks.Remove(current = await Task.WhenAny(tasks)), 
            () => current,
            async () => { });
    });
}

One can then process the tasks in completion order, e.g. returning the first matching one as requested:

await WhenCompleted(tasks).FirstOrDefault(t => t.Status == TaskStatus.RanToCompletion)