ParallelForEachAsync

public static Task ParallelForEachAsync<T>(
    IEnumerable<T> source,
    int degreeOfParallelization,
    Func<T, Task> body)
{
    async Task AwaitPartition(IEnumerator<T> partition)
    {
        using (partition)
        {
            while (partition.MoveNext())
            {
                await body(partition.Current).ConfigureAwait(false);
            }
        }
    }
    return Task.WhenAll(
        Partitioner
            .Create(source)
            .GetPartitions(degreeOfParallelization)
            .AsParallel()
            .Select(AwaitPartition));
}