Pick all that apply

• 1Choice 1.

  There's no rule that you need one context per thread. You can take a temporary context per unit of work with performBackgroundTask, save, and throw it away

• 2Choice 2.

  Using one viewContext from four threads wrapped in perform serializes the work, so it's safe and costs the main thread nothing

• 3Choice 3.

  For a change saved on a background context to show up on screen, you need viewContext.automaticallyMergesChangesFromParent = true or you have to merge the didSave notification yourself

• 4Choice 4.

  Four contexts saving the same record at once can conflict, so it's safer to set a mergePolicy, or to run the upsert by server id serially on one background context

• 5Choice 5.

  Collecting NSManagedObjects created on a background context into an array and reading them on the main thread is safe because they're value types