C# ForEachAsync. Allows you to do sequential awaited tasks.(Set paralllelism to 1)

ForEachAsync.cs

public static async Task<IEnumerable<U>> ForEachAsync<T, U>(this IEnumerable<T> items, Func<T, Task<U>> func, int _degreeOfParallelism = 100)
        {
            var results = new List<U>();
            using (var semaphore = new SemaphoreSlim(_degreeOfParallelism))
            {
                var tasks = items.Select(async item =>
                {
                    await semaphore.WaitAsync();
                    try
                    {
                        var result = await func(item);
                        results.Add(result);
                    }
                    finally
                    {
                        semaphore.Release();
                    }
                }).ToArray();

                await Task.WhenAll(tasks);

                return results;
            }
        }