AsyncMOC.m

@autoreleasepool {
    NSCondition *cond = [[NSCondition alloc] init];
    [cond lock];
    @autoreleasepool {
        // Use __block and uncomment below for this to work correctly.
        NSManagedObjectContext * /*__block*/ context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        NSManagedObjectContext * __weak weakContext = context;
        NSManagedObject * __block obj;
        [context performBlockAndWait:^{
            context.persistentStoreCoordinator = persitentStoreCoordinator();
            obj = [NSEntityDescription insertNewObjectForEntityForName:@"Entity"
                                                inManagedObjectContext:context];
            [context save:nil];
        }];
        NSLog(@"weakContext is not nil: %@", weakContext);
        [context performBlock:^{
            [cond lock];
            //NSLog(@"context is not nil: %@", context);
            NSLog(@"weakContext is nil: %@", weakContext);
            NSLog(@"obj.managedObjectContext is not nil? %@", obj.managedObjectContext);
            [obj.managedObjectContext performBlock:^{
                [cond lock];
                // Run in Instruments and this shows sending a message to a zombie object.
                NSLog(@"Objects: %@", obj.managedObjectContext.registeredObjects);
                // Uncomment this and it works!
                // context = nil;
                [cond signal];
            }];
            [cond unlock];
        }];
    }
    [cond wait];
}