pkcs11Interop problem with WaitForSlotEvent when reader is removed

I set up pkcs11Interop Library as follows

Pkcs11Library = PkcsFactories.Pkcs11LibraryFactory.LoadPkcs11Library(PkcsFactories, pkcs11LibraryPath, AppType.MultiThreaded)

I then immediately use a WPF DispatcherTimer which contains the WaitForSlotEvent

        Private Sub CardInsertedTimer_Tick(sender As Object, e As EventArgs)
            Dim eventHappened As Boolean
                Dim id As ULong

                Pkcs11Library.WaitForSlotEvent(WaitType.NonBlocking, eventHappened, id)

            If eventHappened Then
                Debug.Print("CardInsertedEvent - Event - Event: " + eventHappened.ToString + "  ID: " + id.ToString)
            End If
        End Sub

I hope there are no surprises here. If the Slot (which is a USB smart card reader) is removed then I get a C_WaitForSlotEvent returned CKR_DEVICE_ERROR.

Is a DispatcherTimer ok for WaitForSlotEvent?
What should I do to avoid C_WaitForSlotEvent CKR_DEVICE_ERROR?
Does pkcs11Interop handle the adding and removing of slots (ie. SmartCard Readers)?
If pkcs11Interop does not handle adding and removing slots is polling the only way and what would be the best to poll?

Solution

> Is a DispatcherTimer ok for WaitForSlotEvent?

It should be OK in general. You might also consider using WaitForSlotEvent in blocking mode called from a separate thread.

> What should I do to avoid C_WaitForSlotEvent CKR_DEVICE_ERROR?

You need to ask the vendor of your unmanaged PKCS#11 library.

AFAIK C_WaitForSlotEvent was designed for token/card related events not for slot/reader related events. PKCS#11 specification states that when you add or remove slot/reader you might need to reload PKCS#11 library or even restart OS:

On some platforms, or earlier PKCS11 compliant libraries, it may be necessary to successfully call C_Initialize or to restart the entire system.

> Does pkcs11Interop handle the adding and removing of slots (ie. SmartCard Readers)?

Pkcs11Interop does nothing else but gives you access to unmanaged function C_WaitForSlotEvent described in PKCS#11 specification.

> If pkcs11Interop does not handle adding and removing slots is polling the only way and what would be the best to poll?

See answer to first question.