PrintServer.GetPrintQueues throws NullReferenceException

[wstaelens]

Description

when calling GetPrintQueues I sometimes get a NullReferenceException (not always)

Reproduction Steps

          var server = new System.Printing.PrintServer();
        var queues = server.GetPrintQueues(new[] { EnumeratedPrintQueueTypes.Local, EnumeratedPrintQueueTypes.Connections });

Expected behavior

never having a nullreference exception

Actual behavior

sometimes (don't know how to reproduce it) I get a NullReferenceException. (feels like it happens the first time something needs to be initialised.)

Regression?

No response

Known Workarounds

No response

Impact

No response

Configuration

.net 7 latest
windows 10 x64 22h2
vs2022 pro any cpu

Other information

when looking at https://github.com/dotnet/wpf/blob/main/src/Microsoft.DotNet.Wpf/src/System.Printing/ref/System.Printing.cs#L393 I see that it throws null, but I have print queues as a result, sometimes it throws null, but don't know why exactly.

[lindexi]

@wstaelens https://github.com/dotnet/wpf/blob/main/src/Microsoft.DotNet.Wpf/src/System.Printing/ref/System.Printing.cs#L393 is the reference project. In other words, it do not run in the user's devices. So I do not think it will cause any issues.

It will be helpful, if you can append the exception stacktrace.

[wstaelens]

well the strange thing is that we sometimes get a nullreference.
I'll try to see if I can get a stacktrace. Onlything is that I can't force it to reproducing it.

If feels like it happens when something is taking too much time or is initializing. Because 99% of the time I get the queues but sometimes i get that null result. (don't know if it might be related to VS and its debugging context or not)

[wstaelens]

stacktrace:

   at System.Printing.Activation.PrintSystemObjectFactory.Instantiate(Type objType, String[] propertiesFilter)
   at MS.Internal.PrintWin32Thunk.EnumDataThunkObject.GetPrintSystemValuesPerPrintQueues(PrintServer printServer, EnumeratedPrintQueueTypes[] flags, Queue`1 printObjectsCollection, String[] propertyFilter)
   at System.Printing.PrintQueueCollection..ctor(PrintServer printServer, String[] propertyFilter, EnumeratedPrintQueueTypes[] enumerationFlag)
   at System.Printing.PrintServer.GetPrintQueues(EnumeratedPrintQueueTypes[] enumerationFlag)
   at <hidden>.InstalledPrinters() in <hidden>\PrinterSettingsEx.cs:line 153

[lindexi]

@wstaelens It seems that you are using a disposed PrintSystemObjectFactory object.

[wstaelens]

Just calling GetPrintQueues so don't see why it is disposed or why i'm using disposed one.
Something strange is happening.

I've noticed that sometimes after adding a new printer, the Windows Control panel freezes and after 30seconds or a few minutes it loads fine. Must be something in Windows which has been changed and maybe relates to this. Anyone else experiencing thing?