Question

We have a registration-type system that sends a confirmation e-mail once completed. The system had around 3000 registrations within a few minutes and we noticed a bug. If user A registers a few ms after user B has registered, user A will get user B’s details via e-mail. We did manage to fix the issue and I narrowed it down to this piece of code that gets the e-mail template from the cache and just does a string replace on a place holder.

private string ProcessEmailBody(MyRegistrationModel registration)
{
    var content = CacheHelper.GetContent("REGISTRATIONEMAIL");

    if (content != null)
    {
        content.Text = context.Text.Replace("@@FULL_NAME@@", registration.FullName);

        return content.Text;
    }
    else return null;
}

The CacheHelper.GetContent() method is static and I fixed this “bug” by doing this:

private string ProcessEmailBody(MyRegistrationModel registration)
{
    var content = CacheHelper.GetContent("REGISTRATIONEMAIL");

    if (content != null)
    {
        string body = content.Text;
        body = body.Replace("@@FULL_NAME@@", registration.FullName);

        return body;
    }
    else return null;
}

And I can’t figure out for the life of me why this has fixed the issue. Can anybody shed any light on this?

EDIT: Here’s my GetContent() method (I know the signatures are different than above, I was being brief)

public static Content GetContent(string key, int partnerSiteId, int? version, IContentRepository contentRepository, out string cacheKey)
{
    cacheKey = string.Format("{0}_{1}_{2}", key, partnerSiteId, version);

    var content = CacheManager.Get(cacheKey, () => contentRepository.GetContent(key, partnerSiteId, version), WebConfig.GetCacheDuration(CacheProfile.Short));

    return content;
}

private static DataCache _Cache = null; // DataCache is from AppFabric (Microsoft.ApplicationServer.Caching)

public static T Get<T>(string objectKey, Func<T> reloadItemExpresion, TimeSpan cacheDuration) where T : class
{
    if (_Cache == null)
    {
        if (reloadItemExpresion != null)
        {
            return reloadItemExpresion.Invoke();
        }

        return null;
    }

    object cachedObject = null;

    try
    {
        cachedObject = _Cache.Get(objectKey);
    }
    catch (Exception ex)
    {
        if (ex is FileNotFoundException)
        {
            _Cache.Remove(objectKey);
        }
    }

    if (cachedObject != null)
    {
        return cachedObject as T;
    }

    if (reloadItemExpresion != null && cacheDuration > TimeSpan.Zero)
    {
        T item = reloadItemExpresion.Invoke();

        if (item != null)
        {
            Insert(item, objectKey, cacheDuration);
        }

        return item;
    }

    return null;
}

contentRepository.GetContent just goes off to the database and fetches the actual content back.

Answer 1

The first time through you replace the "@@FULL_NAME@@" tag in context.Text with the details of the first user. Once you do that, it never goes back to "@@FULL_NAME@@" again, so everybody gets that dude’s details until your cache is reset. You should avoid modifying objects that you get from cache:

private string ProcessEmailBody(MyRegistrationModel registration) {
    var content = CacheHelper.GetContent("REGISTRATIONEMAIL");
    return content != null ? content.Replace("@@FULL_NAME@@", registration.FullName) : null;
}