How to limit method usage per amount of time?

Question

It has to be trivial, but I just cannot get through it. I have to limit amount of tasks (let's say connections, emails sent or clicks in the button) per amount of time. So e.g. I can send 1000 emails per hour.

How can I do that in c#? I don't know and don't care how much time each operation will take. I just want to make sure that for last hour, only 1000 will be executed.

Answer 1

 class EventLimiter
 {
    Queue<DateTime> requestTimes;
    int maxRequests;
    TimeSpan timeSpan;

    public EventLimiter(int maxRequests, TimeSpan timeSpan)
    {
        this.maxRequests = maxRequests;
        this.timeSpan = timeSpan;
        requestTimes = new Queue<DateTime>(maxRequests);
    }

    private void SynchronizeQueue()
    {
        while ((requestTimes.Count > 0) && (requestTimes.Peek().Add(timeSpan) < DateTime.UtcNow))
            requestTimes.Dequeue();
    }

    public bool CanRequestNow()
    {
        SynchronizeQueue();
        return requestTimes.Count < maxRequests;
    }

    public void EnqueueRequest()
    {
        while (!CanRequestNow())               
            Thread.Sleep(requestTimes.Peek().Add(timeSpan).Subtract(DateTime.UtcNow));
            // Was: System.Threading.Thread.Sleep(1000);

        requestTimes.Enqueue(DateTime.UtcNow);
    }
 }