[Feature] MsalCacheHelper does not work with 100+ threads

[ranmusic]

Hi, we have a customer complaining on the following error when running different threads on the same process, using out .NET SDK:

We are using MsalCacheHelper for dealing with this file, Register to the TokenCache when creating PublicClientApplication on AuthN request

Which version of MSAL.NET are you using?
Microsoft.Identity.Client.Extensions.Msal 2.18.9

Platform
Net Framework 4.7.2

What authentication flow has the issue?
Kusto .NET SDK user prompt.

Is this a new or existing app?
Already in production, probably not many customers are using multi-threads with UserPromptAuthentication.

[bgavrilMS]

Workaround is for the user to close the app and manually delete the lock file.

[ranmusic]

Workaround is for the user to close the app and manually delete the lock file.

With this workaround he will get the problem again when running his app again... :)

[bgavrilMS]

I think it is thread safe, but it does not support hundreds of threads, as you do here. Since each thread needs to lock the file, the contention is too high and

If you want to support this high number of threads, you need to design a different token caching. The current one was not designed for this scenario. For example see https://stackoverflow.com/questions/3503833/cross-process-read-write-synchronization-primative-in-net or a file based cache using Read / Write locks.

It would be too difficult to modify the existing caching strategy, as it would most likely break backwards compat for existing apps.