change to concurrent dictionary

[jasonliao-cb]

[jasonliao-cb]

this is for issue https://github.com/ligershark/WebOptimizer/issues/228

[daneSchilling]

I was able to replicate similar issues by running parallel tasks racing to make the first request to GenerateCacheKey on a single instance of Asset. With the change above, I am able to run parallel tasks without issue.

With the tests I created, I was getting NullReferenceException on the code: asset.Items[PhysicalFilesKey] = files;

[daneSchilling]

@jasonliao-cb I would love for this to get merged. Maybe add the author as the reviewer? They may ask you to remove the unrelated gitignore changes. Thanks again for opening the PR!

[madskristensen]

Thanks

[daneSchilling]

Thank you!

[exileDev]

@madskristensen Can you publish the latest version?

[madskristensen]

Yes, releasing now...