Question

  Public Enum ERight
    ECanInvite = 0
    ECanCreate = 1
    ECanDelete = 2
    etc...
  End Enum


  Public Enum EUserType
    EAdministrator = 0
    EPartner_level1 = 1
    EPartner_level2 = 2
    ENormalUser = 3
    ...etc
  End Enum

This below sub, on rights.add, sometimes throws this error: An item with the same key has already been added.

How is this even possible?

Private Shared rights As Dictionary(Of ws_garuda.EUserType, List(Of ERight)) = Nothing

Private Sub initRoles()
    rights = New Dictionary(Of EUserType, List(Of ERight))
    rights.Clear()
    ' Set all rights to false for all roles
    For Each usertype As EUserType In DirectCast([Enum].GetValues(GetType(EUserType)), EUserType())
      rights.Add(usertype, New List(Of ERight))
    Next
End sub

Answer 1

The error is happening because you’re writing a Shared object in a multithreaded environment.

The fix is to add a lock (in which case the call to Clear() becomes redundant):

Private Shared rights As Dictionary(Of ws_garuda.EUserType, List(Of ERight)) = Nothing
Private Shared rightsLock As Object = New Object()

Private Sub initRoles()
  SyncLock rightsLock
    rights = New Dictionary(Of EUserType, List(Of ERight))
    ' Set all rights to false for all roles
    For Each usertype As EUserType In DirectCast([Enum].GetValues(GetType(EUserType)), EUserType())
      rights.Add(usertype, New List(Of ERight))
    Next
  End SyncLock
End sub