ASP.NET cache objects read-write

Question

what happens if an user trying to read HttpContext.Current.Cache[key] while the other one trying to remove object HttpContext.Current.Cache.Remove(key) at the same time?

Just think about hundreds of users reading from cache and trying to clean some cache objects at the same time. What happens and is it thread safe?

Is it possible to create database aware business objects in cache?

Answer 1

The built-in ASP.Net Cache object (http://msdn.microsoft.com/en-us/library/system.web.caching.cache.aspx) is thread-safe, so insert/remove actions in multi-threaded environments are inherently safe.

Your primary requirement for putting any object in cache is that is must be serializable. So yes, your db-aware business object can go in the cache.

Answer 2

If the code is unable to get the object, then nothing / null is returned.

Why would you bother to cache an object if you would have the chance of removing it so frequently? Its better to set an expiration time and reload the object if its no longer in the cache.

Can you explain "DB aware object"? Do you mean a sql cache dependency, or just an object that has information about a db connection?

EDIT: Reponse to comment #3.

I think we are missing something here. Let me explain what I think you mean, and you can tell me if its right.

1. UserA checks for an object in cache ("resultA") and does not find it.
2. UserA runs a query. Results are cached as "resultA" for 5 minutes.
3. UserB checks for an object in cache ("resultA") and does find it.
4. UserB uses the cached object "resultA"

If this is the case, then you dont need a Sql Cache dependency.

Answer 3

Well i have a code to populate cache:

string cacheKey = GetCacheKey(filter, sort);
if (HttpContext.Current.Cache[cacheKey] == null)
{
  reader = base.ExecuteReader(SelectQuery);
  HttpContext.Current.Cache[cacheKey] = 
    base.GetListByFilter(reader, filter, sort);
}
return HttpContext.Current.Cache[cacheKey] as List<CurrencyDepot>;

and when table updated cleanup code below executing:

private void CleanCache()
{
  IDictionaryEnumerator enumerator = 
    HttpContext.Current.Cache.GetEnumerator();
  while (enumerator.MoveNext())
  {
    if (enumerator.Key.ToString().Contains(_TableName))
    {
      try {
        HttpContext.Current.Cache.Remove(enumerator.Key.ToString());
      } catch (Exception) {}
    }
  }
}

Is this usage cause a trouble?