One of the hidden gems in DotNetNuke 5.0 is the new caching support in the CBO (Custom Business Objects) class. During the refactoring of DotNetNuke for the Cambrian release, caching was one of the things that was closely looked at, since caching was starting to cause major issues in the DNN 4.x branch.

Lets take a look at how caching was done in DNN 4:

Public Shared Function GetSecureHostSettings() As Hashtable
Dim h As Hashtable
h = CType(DataCache.GetCache("GetSecureHostSettings"), Hashtable)
If h Is Nothing Then
h = New Hashtable
Dim SettingName As String
Dim dr As IDataReader = DataProvider.Instance().GetHostSettings
While dr.Read()
If Not Convert.ToBoolean(dr(2)) Then
SettingName = dr.GetString(0)
If SettingName.ToLower.IndexOf("password") = -1 Then
If Not dr.IsDBNull(1) Then
h.Add(SettingName, dr.GetString(1))
Else
h.Add(SettingName, "")
End If
End If
End If
End While
dr.Close()
DataCache.SetCache("GetSecureHostSettings", h)
End If
Return h
End Function

 

This is code from the class DotNetNuke.Entities.Host.HostSettings in DNN 4.9.3. In fact this is a pattern that is used throughout the application in DNN 3.x – 4.x. The problem with this pattern is that it is not completely thread safe, especially if it is used in larger routines, and specifically on large and busy sites. There might be a chance that the object you get from the cache is removed from cache when you want to use it.

In DotNetNuke 5.x, the CBO class was beefed up with a new caching function:

Public Shared Function GetCachedObject(Of TObject)(ByVal cacheItemArgs As CacheItemArgs, ByVal cacheItemExpired As CacheItemExpiredCallback) As TObject
Return DataCache.GetCachedData(Of TObject)(cacheItemArgs, cacheItemExpired)
End Function

which in turn calls a new method of DataCache, GetCachedData. This method looks like this:

Public Shared Function GetCachedData(Of TObject)(ByVal cacheItemArgs As CacheItemArgs, ByVal cacheItemExpired As CacheItemExpiredCallback) As TObject
'Declare Local Variable and try and retieve it from the cache
Dim objObject As Object = GetCache(cacheItemArgs.CacheKey)
Dim timeOut As Integer = cacheItemArgs.CacheTimeOut * Convert.ToInt32(Host.PerformanceSetting)
'If Item is not cached
If objObject Is Nothing Then
'Prevent other threads from entering this block while we regenerate the cache
SyncLock objLock
'Try to retrieve object from Cache again (in case another thread loaded the object since we first checked)
objObject = GetCache(cacheItemArgs.CacheKey)
If objObject Is Nothing Then
'Get Object from data Source using Delegate
objObject = cacheItemExpired(cacheItemArgs)
If objObject IsNot Nothing AndAlso timeOut > 0 Then
DataCache.SetCache(cacheItemArgs.CacheKey, objObject, cacheItemArgs.CacheDependency, Cache.NoAbsoluteExpiration, _
TimeSpan.FromMinutes(timeOut), cacheItemArgs.CachePriority, cacheItemArgs.CacheCallback)
'Check if Item was actually saved in the cache
If DataCache.GetCache(cacheItemArgs.CacheKey) Is Nothing Then
Dim objEventLogInfo As New LogInfo
objEventLogInfo.LogTypeKey = EventLogController.EventLogType.CACHE_ERROR.ToString()
objEventLogInfo.LogProperties.Add(New LogDetailInfo(cacheItemArgs.CacheKey, "Not Created"))
Dim objEventLog As New EventLogController()
objEventLog.AddLog(objEventLogInfo)
End If
ElseIf objObject Is Nothing Then
Return Nothing
End If
End If
End SyncLock
End If
Return DirectCast(objObject, TObject)
End Function
 

As you can see, this is basically still the same pattern as the “old” pattern in DNN 3.x/4.x, however, with a few enhancements:

  • Thread safety. Using Synlock, other threads are prevented to intrude when we are handling the object
  • automatic callback is used, that will get called when the object is not found in cache
  • check to ensure object was saved to cache correctly

 

As an example of the usage of the new pattern, let’s see how Host.GetSecureHostSettings was modified in DNN 5:

Public Shared Function GetSecureHostSettingsDictionary() As Dictionary(Of String, String)
Return CBO.GetCachedObject(Of Dictionary(Of String, String))(New CacheItemArgs(DataCache.SecureHostSettingsCacheKey, _
DataCache.HostSettingsCacheTimeOut, _
DataCache.HostSettingsCachePriority), _
AddressOf GetSecureHostSettingsDictionaryCallBack)
End Function

And the corresponding callback function:

Private Shared Function GetSecureHostSettingsDictionaryCallBack(ByVal cacheItemArgs As CacheItemArgs) As Object
Dim dicSettings As New Dictionary(Of String, String)
Dim dr As IDataReader = DataProvider.Instance().GetHostSettings
Try
While dr.Read()
If Not Convert.ToBoolean(dr(2)) Then
Dim settingName As String = dr.GetString(0)
If settingName.ToLower.IndexOf("password") = -1 Then
If Not dr.IsDBNull(1) Then
dicSettings.Add(settingName, dr.GetString(1))
Else
dicSettings.Add(settingName, "")
End If
End If
End If
End While
Finally
If Not dr Is Nothing Then
dr.Close()
End If
End Try
Return dicSettings
End Function

 

As you can see, the callback function GetSecureHostSettingsDictionaryCallBack is essentially the same as the old method, minus the caching logic. It has become far more easier to use caching in your own module using this pattern. A few lines of code will do the trick.

* this is a repost of a post over on dotnetnuke.com

Posted in: DotNetNuke

Comments

Andrew H
# Andrew H
Tuesday, November 03, 2009 11:05 AM
Interesting article, but I don't quite understand the bug. I can see that caching may be less successful than desired because SetCache may be done by more than one thread, however your post suggests that you will fail to get the desired object and I can't see that happening. Since you try to get the cached object and then check if Nothing was returned, surely if it fails all that happens is an extra database hit. Is that the concern (not very efficient) or is there a risk of a race condition or exception that I'm failing to spot?

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 I am Erik van Ballegoij. I work for DotNetNuke corporation as Technical Lead and Evangelist. On this blog I blog about DotNetNuke tips and tricks and whatever else comes to mind

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