Core Data code and multithreading - multithreading

Question

The following code is fetch data (fill data for the first time) part of my tableViewController. I am using an NSManagedDocument's managedObjectContext to fill (pre populate) my database. The source is an array that I clean up from my TXT file which rests directly in the Xcode's resources folder. After this creation, I have document cases like closed / open and normal.
The following code inputs and fetches my data onto the table correctly with a fetched results controller request. However, when the data is loading in the thread that is meant to free the UI from this one time data creation (26854 object names) into managedObject.name attribute heavy operation, the tableview and my UI is frozen (for 1-15 seconds that is I think while populating in document.managedObjectContext for the first time for my database).
After 10-15 seconds data is loaded and shows correctly. However, when I stop the simulator and restart the app in simulator, although I save the document as seen in below code, and I use the same fetch results controller setup (and request) the table view shows empty, it is movable in this case (The document state shows open and normal at this stage and file path is same, I checked... It seems like neither autosave nor explicit saveForOverwriting I use work... Or is it something else? I tried a lot of things and I'll go crazy soon. I think it has something to do with my multithreading.
self.managedObjectNames is the array property in the table view and I set it from the TXT file during my table view's loadView:
Is there anybody out there who can show the mistake here? Is it that I give self.managedObjectNames in the method of entity creation category.
Thanks!
- (void)fetchDataIntoDocument:(UIManagedDocument *)document {
dispatch_queue_t fetchQ = dispatch_queue_create("Data fetcher", NULL);
dispatch_async(fetchQ, ^{
[document.managedObjectContext performBlock:^{
for (int i = 0; i < 26854; i++) {
[managedObject managedObjectWithId:[NSNumber numberWithInt:i] andArray:self.managedObjectNames inManagedObjectContext:document.managedObjectContext];
}
// NSLog(#"Save baby!!?");
[document saveToURL:document.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:nil];
}];
});
dispatch_release(fetchQ);
}

Answer 1

The reason why your UI is blocked for 10-15 seconds is because the document.managedObjectContext has been created with NSMainQueueConcurrencyType. That means that the performBlock: method will be executed on the main queue.
Creating the fetchQ in your code does not have any reason. It would have a reason if fetching of data would take some considerable amount of time but adding them would be fast (e.g. creating/modifying only few objects):
dispatch_async(fetchQ, ^{
// fetch data here (e.g. fetchAttribute may take few seconds)
NSString *attribute = fetchAttribute();
[document.managedObjectContext performBlock:^{
MyObject *o;
o = [NSEntityDescription insertNewObjectForEntityForName:#"MyObject"
inManagedObjectContext:document.managedObjectContext];
o.myAttribute = attribute;
}];
});
However I don't know answer to your main question.