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1/16/2006 10:13 PM
 
User is offline James Webster

www.mhs87.com
Joined: 12/30/2005
Posts: 63

I've noticed in quite a few places that the root cause for exceptions is the pattern I see DataCache.GetCache() used.

The patten that I see is:

If (DataCache.GetCache("object") Is Nothing)
   Dim obj = code for loading config from files
   DataCache.SetCache("object", obj)
End If
Return DataCache.GetCache("object")

The problem I'm seeing is there is a time window between the SetCache and the final return that can result in the cache being thrown out, especially when multithreaded operations are happening.

Wouldn't the following pattern make more sense?

Dim obj = DataCache.GetCache("object")
If obj Is Nothing
   obj = code for loading config from files
   DataCache.SetCache("object", obj)
End If
Return obj

 
 
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1/21/2006 11:14 PM
 
User is offline James Webster

www.mhs87.com
Joined: 12/30/2005
Posts: 63

Maybe no one cares...  but I went through my entire project and here are the files that had what appears to be a potential timing issue bug (search for DataCache.GetCache).  The interesting thing is out of 27 files, only these 8 followed this pattern.  The rest followed the pattern I suggested.

Domain.vb
Configuration.vb
XMLLoggingProvider.vb
RewriterConfiguration.vb
ClientAPI.vb
UserOnlineController.vb
Localization.vb
SiteLogController.vb

After putting the changes on my site, the number of exceptions I ran into significantly diminished.
 
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1/23/2006 7:47 AM
 
User is offline Vicenç Masanas


Vicenç Masanas's Avatar

Vicenç Masanas's Avatar

www.disgrafic.com
Joined: 9/16/2003
Posts: 1817
James,
I'm very interesed in this changes and wanted to know if this change continues to look as the root of these exceptions.
Please if you're monitoring your system and let us know if this was the root problem.
Disgrafic.com
 
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1/24/2006 6:27 AM
 
User is offline James Webster

www.mhs87.com
Joined: 12/30/2005
Posts: 63

Without digging deeper into how the Cache expires, I can't say for sure this is the root issue.  That said, coding practices do say that you shouldn't return something you haven't verified to be null if the callers are not expecting null.  I also suspect the call would be faster allocating on object on the heap and assigning it once, rather then making another stack call to the cache function, though I'd have to verify that through ILSAM.

On my server, the random null reference exceptions I was getting for various functions all went away after making these changes.  The only exception I'm getting now is intermitent Thread Abort exceptions on the scheduler threads and a couple exceptions for the Forum module that I'd still trying to track down.

If you want details of the changes I made, I can either post or send a diff.

James
 
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1/24/2006 7:12 AM
 
User is offline Paul Davis

Paul Davis's Avatar

www.phdavis.com
Joined: 4/26/2004
Posts: 616

Hey james,

Could you send me a diff?  It sounds like it would clear up a lot off errors I'm seeing on my sites.  I get referals from google andmsn search that reference pages that have moves or no longer exist and the search engines aren't picking up on the 301's I send back but DNN generates the cache error you discribe.

Paul Davis
 
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