The goal is to find the parent activity of the activity we are trying to update - this information is stored in the continuations ...

'

              -- The goal is to find the parent activity of the activity we are trying to update
              -- this information is stored in the continuations table. Since we are making decisions
              -- based on this value, we need to prevent users from updating this value after we read, or
              -- if we find nothing, we need to prevent them from inserting a value. To prevent insertion,
              -- we take an applock on the ActivityID and our protocol requires that before a continuation is
              -- added an exclusive applock will be taken on our id. To prevent it from changing, we use
              -- repeatable read locks. The value could change if our current parent turns out to not be the 
              -- root and so when his continuation is established, we would be pointed to his new parent.
            
              DECLARE @@ret INT
              EXEC @@ret = sp_getapplock @ContinuationToken, 'Exclusive', 'Transaction', 100
              IF (@@ret < 0)  -- lock not granted
              BEGIN
                RAISERROR('Lock not granted', 16, 1)
                RETURN
              END
              
              -- Current trace's parent may also be continuation, find the root (main trace).
              DECLARE @@rootTrace NVARCHAR(128)

              DECLARE @@parentTemp NVARCHAR(128)
              SET @@parentTemp = @ParentActivityID
              WHILE (@@parentTemp IS NOT NULL)
              BEGIN
                  SET @@rootTrace = @@parentTemp

                  EXEC @@ret = sp_getapplock @@parentTemp, 'Shared', 'Transaction', 100
                  IF (@@ret < 0)  -- lock not granted
                  BEGIN
                    RAISERROR('Lock not granted', 16, 1)
                    RETURN
                  END

                  SET @@parentTemp = NULL
                  SELECT @@parentTemp = ParentActivityID 
                  FROM