Making com.apple.CoreData.ConcurrencyDebug 1 work

Question

I am trying to migrate some code to use an NSManagedObjectContext with NSPrivateQueueConcurrencyType.

I\'m sometimes getting very odd error

Answer 1

The argument -com.apple.CoreData.ConcurrencyDebug is available from iOS > 8 and OSX > 10.10 : make sure you target the right platform.

The console should log this if the flag is enabled :

CoreData: annotation: Core Data multi-threading assertions enabled.

Source : Core Data Concurrency Debugging from Ole Begemann

Answer 2

Working with XCode 8.x and iOS 10.x, I wanted to provide a streamlined answer for anyone wanting to implement this now.

You will first need to modify the scheme for your app:

Once you select Scheme, select Edit Scheme which should appear near the bottom of your list:

When opened, make sure that you have Run selected and choose Arguments. You will want to copy the following values in:

• -com.apple.CoreData.ConcurrencyDebug 1
• -com.apple.CoreData.Logging.stderr 1

Your screen should look like this:

After launching the app, you should see this appear in your console now when those options are enabled:

CoreData: annotation: Core Data multi-threading assertions enabled.

And when you run into an exception generated by this, you will likely see this:

CoreData`+[NSManagedObjectContext Multithreading_Violation_AllThatIsLeftToUsIsHonor]:

You can return to the scheme editor and disable this logging as needed to prevent exceptions in the future.