CODEWITHSUNDEEP
iosobjective-cmultithreadingdebuggingcore-data
Bharat Jagtap
Bharat Jagtap

Reputation: 1692

Core Data crash on [managedObjectContext reset];

Here is the code snippet of my core data operation . It works fine most of the time. But now when I added core data debugging argument to see if all the core data calls are fine with respect to multithreading Core Data Concurrency Debugging , I see a crash on the line [contexts reset]; .

- (void)readAllModelObjects {

NSFetchRequest * fr = [NSFetchRequest ....]

NSManagedObjectContext * context = [selg getChildContext];

   [context performBlockAndWait:^{

         NSArray * resultArray = [context executeFetchRequest:fr error: nil ];

         NSArray * nonCoreDataModelObjectsArray = [self parseCoreDataObjectsToModel: resultArray];

        _memberResultArray = nonCoreDataModelObjectsArray ;

   }];

   [context reset]; // This is the line it crashes .    
}


 - (NSManagedObjectContet *)getChildContext {

    NSManagedObjectContext * privateContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

    privateContext.parentContext = [self mainQueueManagedObjectContext];

    return privateContext ;
  }


 - (NSArray * )parseCoreDataObjectsToModel:(NSArray *)cdObjectsArray {

     // creates and initializes the model objects array (non managed object class objects ) from core data objects
     // return this array
  }

I got below error from core data 

 CoreData`+[NSManagedObjectContext _ 
 _Multithreading_Violation_AllThatIsLeftToUsIsHonor__]:

Any hints / suggestions will definitely help me in figuring out the crash , please help .

Upvotes: 1

Views: 1199

Answers (1)

Jon Rose
Jon Rose

Reputation: 8563

When you change values of a managedObject those changes are not saved until the context is saved. Once you save the context, the context either writes to disk or pushes it up to its parent context. This is a way to have a few changes that are all done as one unit - in database speak it would be called a transaction. reset undoes those changes. So just like changing object needs to be done on the correct thread, reset which undoes the changes, needs to be done on the correct thread.

In your case, there is no need to call reset at all because you haven't changed anything to context. The context doesn't have any changes that would be undo by a reset. If you would want to call reset you would have to do inside the performBlockAndWait.

TD;DR : [context reset] is not thread-safe and must be done from the correct thread.

Upvotes: 2

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