Generated NSManagedObject subclasses leak when re-creating Core Data stacks from scratch

Number:rdar://FB7723824 Date Originated:June 3, 2020
Status:Open Resolved:
Product:Core Data Product Version:iOS 13
Classification:Application Slow/Unresponsive Reproducible:Yes
When creating and tearing down Core Data stacks from scratch, classes generated at run time are not released. This leads to significant memory bloat but also leads to a very slow lookup in a hash table containing the generated classes.

An example project that reproduces the issue has been attached.

This issue occurs in a unit test suite which re-creates the entire Core Data stack so each test has a clean slate. In large test bundles, the hash table grows large enough to cause the tests to slow down significantly.

General flow for reproducing this issue:

    NSURL *url = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@".momd"];
    for(int i = 0; i < 2000; i++) {
        NSManagedObjectModel *model = [[NSManagedObjectModel alloc] initWithContentsOfURL:url];
        NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];
        NSPersistentStore *store = [psc addPersistentStoreWithType:NSInMemoryStoreType configuration:nil URL:nil options:nil error:nil];

        NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        context.persistentStoreCoordinator = psc;

        __unused MainEntity *obj = [NSEntityDescription insertNewObjectForEntityForName:@"MainEntity" inManagedObjectContext:context];
        [context save:NULL];

        [psc removePersistentStore:store error:NULL];

Running the example project will run this code and display a prompt to open the Memory Graph Debugger to view the objects in question.

Example project:


Adding this code seems to bring the performance back to what it was in iOS 12

Method m = class_getInstanceMethod([NSEntityDescription class], @selector(_addFactoryToRetainList:)); method_setImplementation(m, imp_implementationWithBlock(^void(id self, id _unused, int factory){ /// Do nothing }));

Overriding -[NSEntityDescription _addFactoryToRetainList:] to no-op brings us back to iOS 12 perf, but there’s still degraded performance as the number of iterations increases

By eric.amorde at June 8, 2020, 5:53 p.m. (reply...)

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