Throttle Helper

gistfile1.cs

public class Throttle
{
    private Task _control;
    private readonly int _minimumMillis;

    public Throttle(int millis)
    {
        _minimumMillis = millis;
    }

    public void Block()
    {
        // Only block if it's not the first time
        if(_control != null)
        {
            _control.Wait();
        }
        _control = Task.Delay(_minimumMillis);
    }
}

public static class ThrottleExtensions
{
    public static IEnumerable<T> Throttled<T>(this IEnumerable<T> source, int millis)
    {
        var throttle = new Throttle(millis);
        foreach(var item in source)
        {
            throttle.Block();
            yield return item;
        }
    }
}