Limiting the Number of Emails Sent By Elmah

Question

Does anyone know of a good way to limit the number of emails sent by Elmah during a time period like you can with Health Monitoring?

I want to be able to limit the email

Answer 1

I wrote this using the same method as in your question. Seems to work nicely.

public static DateTime  RoundUp(this DateTime dt, TimeSpan d)
{
    return new DateTime(((dt.Ticks + d.Ticks - 1) / d.Ticks) * d.Ticks);
}
static ConcurrentDictionary> _concurrent = new ConcurrentDictionary>();

/// 

/// This is an Elmah event used by the elmah engine when sending out emails. It provides an opportunity to weed out 
/// irrelavent emails.
/// 
/// 
/// 
protected void ErrorMail_Filtering(object sender, ExceptionFilterEventArgs e)
{
    preventSpammingDigestEmail(e);
}

/// 

/// Prevents spamming by throttling emails to 5 minute intervals.
/// 
/// 
private static void preventSpammingDigestEmail(ExceptionFilterEventArgs e)
{
    DateTime roundedTimeStamp = DateTime.Now.RoundUp(TimeSpan.FromMinutes(5));
    string serialisedException = Util.SerializeException(e.Exception);

    var lastRaisedException = new KeyValuePair
        (roundedTimeStamp, serialisedException);

    int key = lastRaisedException.GetHashCode();

    bool errorHasAlreadyBeenRaised = _concurrent.ContainsKey(key);

    // If event has already been raised in the last five minutes dont raise again
    if (errorHasAlreadyBeenRaised)
    {
        e.Dismiss();
        return;
    }

    // Record that it has been raised
    _concurrent.TryAdd(key, lastRaisedException);

    // Clean up existing entries
    Task.Factory.StartNew(() =>
        {
            var toRemove =
                _concurrent.Where(pair => pair.Value.Key < DateTime.Now.Date).Select(pair => pair.Key).ToArray();

            foreach (var i in toRemove)
            {
                KeyValuePair keyValuePair;
                _concurrent.TryRemove(i, out keyValuePair);
            }
        });
}