I'm a beginner with Grand Central Dispatch (GCD) and Core Data, and I need your help to use Core Data with CGD, so that the UI is not locked while I add 40.000 records to Core Data. I know that CD is not thread safe, so I have to use another context, and then save the data and merge contexts, as far as I was able to understand from some articles. What I couldn't do yet, is put the pieces together.