Problem with threads count grow when use OfficeDevPnP AuthenticationManager

Recently we faced with the following problem in our Azure function app: after some time of functioning Azure functions got stuck and the only way to make them work again was to restart them manually from Azure portal UI. Research showed that problem was related with threads count: because of some reason threads count permanently grew to 6K thread after which Azure function app became unresponsive:

We reviewed our code, made some optimizations, change some async calls to sync equivalents, but it didn’t fix the problem. Then we continued troubleshooting and found the following: in the code we used OfficeDevPnP AuthenticationManager in order to get access token for communicating with Sharepoint Online like that:

using (var ctx = new OfficeDevPnP.Core.AuthenticationManager().GetAppOnlyAuthenticatedContext(url, clientId, clientSecret))
{
    ...
}

Note that in this example new instance of AuthenticationManager is created each time when above code was executed. In our case it was inside queue-triggered Azure function which was called quite frequently. Elio Struyf (we worked over this problem together so credits for this finding go to him ) tried to make AuthenticationManager static – i.e. only one instance was created for the whole Azure function worker process:

public static class Helper
{
 private static OfficeDevPnP.Core.AuthenticationManager authMngr = new OfficeDevPnP.Core.AuthenticationManager();

 public static void QueueTriggeredFunc()
 {
  using (var ctx = authMngr.GetAppOnlyAuthenticatedContext(url, clientId, clientSecret))
  {
  ...
  }
 }
}

After that threads count got stabilized with avg 60 threads:

We reported this problem to OfficeDevPnP team and they confirmed that there is problem in AuthenticationManager which internally creates thread for monitoring access token’s lifetime, but this thread is not released when AuthenticationManager got recycled by garbage collector (also need to mention that AuthenticationManager itself was not disposable at the moment when this problem was found. We used OfficeDevPnP 3.20.2004.0 when found this problem). For now this workaround with making AuthenticationManager static was Ok and as far as I know currently OfficeDevPnP team works over correct fix for this problem. So hopefully it will be available soon globally.

Update 2020-06-15: from latest news I've got (thanks to Yannick Plenevaux :) ) OfficeDevPnP team addressed this issue in 202006.2 version and made AuthenticationManager disposable. So you may need to review your code in order to add using() around it.