Process pending async tasks in the order they are completed.

ProcessPendingAsyncTasks.md

public static class TaskExtensions
{
    public static async Task<Task> ProcessCompleted(this IList<Task> tasks)
    {
        if (tasks == null)
        {
            throw new ArgumentNullException(nameof(tasks));
        }
        Task completedTask = await Task.WhenAny(tasks);
        tasks.Remove(completedTask);
        return completedTask;
    }
}