Curious Case Of CoreData

Recently I found an interesting bug on my app. Whenever I pass an object which containt NSManagedObject subclass, at one point of time it will disappear from the memory. I was frustrated and naively change my implementation by passing the unique parameter of NSManagedObject subclass and fetch it from CoreData whenever it disappear. I was happy, things are working well, there was an increase of memory usage but everything run smoothly.

Yesterday I found the same issue again and finally able to uncover amusing mistery.

Aparrantely since NSManagedObject depend on NSManagedObjectContext, without the context you can’t do any, and since the context and threading doesn’t run well together, whenever the thread of context creation is killed by CoreData, the context disappear and your NSManagedObject will fault.

I believe it’s my implementation default on multi threading on CoreData but at least now I know why and how to solve the issue. By ensuring your thread is still active and long live, you should have no issue with NSManagedObjectContext. Now I make sure I only use 2 different context, read and update, which is good enough for my apps.

Would love to explore more about multi threading on CoreData, perhaps there are more intersting stuff I can dig along. It’s an interesting time to live as mobile dev.

Till then, Ciaosz