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Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
Core Data with multiple managed object contexts
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Core Data with multiple managed object contexts

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When using Core Data for persisting app data multiple managed object contexts (MOC) are often required to avoid blocking UI. Typically you would create a background MOC and listen for changes on the …

When using Core Data for persisting app data multiple managed object contexts (MOC) are often required to avoid blocking UI. Typically you would create a background MOC and listen for changes on the main MOC, merging changes as necessary. With iOS 5, MOCs now have parent context and the ability to set concurrency types. These new features greatly simplify dealing with Core Data on background queues. During this presentation Matt will cover the pros and cons of this new method of dealing with Core Data.

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  • 1. Core Datawith multiple managed object contexts Photo by Free-Photo-Gallery.org
  • 2. Core Datawith multiple managed object contexts Photo by Free-Photo-Gallery.org
  • 3. Matt(hew) Morey Senior Developer at ChaiONE Traveler Boardsport Junkie matthewmorey.com | @xzolian
  • 4. Agenda1)Core Data Basics2)Concurrency Problems3)Concurrency Solutions
  • 5. Agenda1)Core Data Basics2)Concurrency Problems3)Concurrency Solutions
  • 6. Basics
  • 7. Basics App NSManagedObject NSManagedObjectContextNSPersistentStoreCoordinator NSManagedObjectModel NSPersistentStore SQLite XML Binary In Memory Custom
  • 8. Basics App NSManagedObject NSManagedObjectContextNSPersistentStoreCoordinator NSManagedObjectModel NSPersistentStore SQLite XML Binary In Memory Custom
  • 9. Managed Object Model
  • 10. Managed Object Model
  • 11. Managed Object Model- (NSManagedObjectModel *)managedObjectModel{ if (_managedObjectModel != nil) { return _managedObjectModel; } NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"core-data" withExtension:@"momd"]; _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL]; return _managedObjectModel;}
  • 12. Persistent Store Coordinator
  • 13. Persistent STore Coordinator- (NSPersistentStoreCoordinator *)persistentStoreCoordinator{ if (_persistentStoreCoordinator != nil) { return _persistentStoreCoordinator; } NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"core-data.sqlite"]; NSError *error = nil; _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]]; if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) { /* Replace this implementation with code to handle the error appropriately. ... */ NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return _persistentStoreCoordinator;}
  • 14. Persistent STore Coordinator- (NSPersistentStoreCoordinator *)persistentStoreCoordinator{ if (_persistentStoreCoordinator != nil) { return _persistentStoreCoordinator; } NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"core-data.sqlite"]; NSError *error = nil; _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]]; if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) { /* Replace this implementation with code to handle the error appropriately. ... */ NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return _persistentStoreCoordinator;}
  • 15. Managed Object Context
  • 16. Managed Object Context- (NSManagedObjectContext *)managedObjectContext{ if (_managedObjectContext != nil) { return _managedObjectContext; } NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { _managedObjectContext = [[NSManagedObjectContext alloc] init]; [_managedObjectContext setPersistentStoreCoordinator:coordinator]; } return _managedObjectContext;}
  • 17. Single Context
  • 18. Single Context
  • 19. Single Context Code Examplehttps://github.com/mmorey/CoreDataMultiContext/tree/blocking
  • 20. Agenda1)Core Data Basics2)Concurrency Problems3)Concurrency Solutions
  • 21. Problems‣Core Data Managed Objects are not thread safe ‣Must pass Object IDs to use across threads‣Objects are locked for all operations including read ‣Objects that feed the UI must be fetched on the main thread
  • 22. Agenda1)Core Data Basics2)Concurrency Problems3)Concurrency Solutions
  • 23. Traditional Multi-ContextPre-iOS 5: Thread Confinement‣Single NSMangedObjectContext per thread‣Manual notifications, merging, and saving‣Fairly easy to understand, but harder to manage
  • 24. Traditional Multi-Context
  • 25. Traditional Multi-Context- (void)loadData{ dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ // Create temp context NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init]; [context setPersistentStoreCoordinator:[(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator]]; // // Do lots of async work here // // Save the context. error = nil; if (![context save:&error]) { // Replace this implementation with code to handle the error appropriately. abort(); } });}// Register for save notification in ViewDidLoad[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:context];
  • 26. Traditional Multi-Context- (void)loadData{ dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ // Create temp context NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init]; [context setPersistentStoreCoordinator:[(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator]]; // // Do lots of async work here // // Save the context. error = nil; if (![context save:&error]) { // Replace this implementation with code to handle the error appropriately. abort(); } });}// Register for save notification in ViewDidLoad[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:context];
  • 27. Traditional Multi-Context- (void)loadData{ dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ // Create temp context NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init]; [context setPersistentStoreCoordinator:[(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator]]; // // Do lots of async work here // // Save the context. error = nil; if (![context save:&error]) { // Replace this implementation with code to handle the error appropriately. abort(); } });}// Register for save notification in ViewDidLoad[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:context];
  • 28. Traditional Multi-Context- (void)contextDidSave:(NSNotification *)notification { dispatch_async(dispatch_get_main_queue(), ^{ NSManagedObjectContext *mainContext = [self.fetchedResultsController managedObjectContext]; [mainContext mergeChangesFromContextDidSaveNotification:notification]; });}// Or- (void)contextDidSave:(NSNotification *)notification { [self.managedObjectContext performSelectorOnMainThread: @selector(mergeChangesFromContextDidSaveNotification:) withObject:notification waitUntilDone:NO];}
  • 29. Traditional Multi-Context- (void)contextDidSave:(NSNotification *)notification { dispatch_async(dispatch_get_main_queue(), ^{ NSManagedObjectContext *mainContext = [self.fetchedResultsController managedObjectContext]; [mainContext mergeChangesFromContextDidSaveNotification:notification]; });}// Or- (void)contextDidSave:(NSNotification *)notification { [self.managedObjectContext performSelectorOnMainThread: @selector(mergeChangesFromContextDidSaveNotification:) withObject:notification waitUntilDone:NO];}
  • 30. Traditional Multi-Context Code Examplehttps://github.com/mmorey/CoreDataMultiContext/tree/notification-context
  • 31. Parent Child Context≥ iOS 5: Parent Child Contexts‣Grand Central Dispatch private dispatch queues‣Threading managed for you, no manual synchronization required‣Less complicated and more flexible than pre-iOS 5 method‣Context can and should be nested
  • 32. Concurrency TypesNSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; ‣NSConfinementConcurrencyType ‣Separate contexts for each thread ‣Default, Legacy option ‣NSPrivateQueueConcurrencyType ‣MOC maintains private serialized queue ‣Can be created from any other thread ‣Idle queues are more efficient than extra threads ‣NSMainQueueConcurrencyType ‣Similar to private queue but on the main queue
  • 33. Parent Child Context
  • 34. Parent Child Context PSC PSC
  • 35. Parent Child Context__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ // // Do lots of async work here // // Save the context. NSError *error = nil; if (![temporaryContext save:&error]) {abort();} [managedObjectContext performBlock:^{ // Save the context. NSError *error = nil; if (![managedObjectContext save:&error]) {abort();} }]; // main}]; // temp context
  • 36. Parent Child Context__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ // // Do lots of async work here // // Save the context. NSError *error = nil; if (![temporaryContext save:&error]) {abort();} [managedObjectContext performBlock:^{ // Save the context. NSError *error = nil; if (![managedObjectContext save:&error]) {abort();} }]; // main}]; // temp context
  • 37. Parent Child Context__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ Private Queue save // // Do lots of async work here // propagates up to parent // Save the context. NSError *error = nil; if (![temporaryContext save:&error]) {abort();} [managedObjectContext performBlock:^{ // Save the context. NSError *error = nil; if (![managedObjectContext save:&error]) {abort();} }]; // main}]; // temp context
  • 38. Parent Child Context__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ Save to disc still locks PS // which will block the UI during // Do lots of async work here // read operations // Save the context. NSError *error = nil; if (![temporaryContext save:&error]) {abort();} [managedObjectContext performBlock:^{ // Save the context. NSError *error = nil; if (![managedObjectContext save:&error]) {abort();} }]; // main}]; // temp context
  • 39. Basics App NSManagedObject NSManagedObjectContextNSPersistentStoreCoordinator NSManagedObjectModel NSPersistentStore SQLite XML Binary In Memory Custom
  • 40. Async Saving - Parent Child Context
  • 41. Async Saving - Parent Child Context// Child context- (NSManagedObjectContext *)managedObjectContext{ if (_managedObjectContext != nil) { return _managedObjectContext; } _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType]; _managedObjectContext.parentContext = [self writerManagedObjectContext]; return _managedObjectContext;}// Parent context- (NSManagedObjectContext *)writerManagedObjectContext{ if (_writerManagedObjectContext != nil) { return _writerManagedObjectContext; } NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { _writerManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType: NSPrivateQueueConcurrencyType]; [_writerManagedObjectContext setPersistentStoreCoordinator:coordinator]; } return _writerManagedObjectContext;}
  • 42. Async Saving - Parent Child Context// Child context- (NSManagedObjectContext *)managedObjectContext{ if (_managedObjectContext != nil) { return _managedObjectContext; } _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType]; _managedObjectContext.parentContext = [self writerManagedObjectContext]; return _managedObjectContext;}// Parent context- (NSManagedObjectContext *)writerManagedObjectContext{ if (_writerManagedObjectContext != nil) { return _writerManagedObjectContext; } NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { _writerManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType: NSPrivateQueueConcurrencyType]; [_writerManagedObjectContext setPersistentStoreCoordinator:coordinator]; } return _writerManagedObjectContext;}
  • 43. Async Saving - Parent Child Context// Child context- (NSManagedObjectContext *)managedObjectContext{ if (_managedObjectContext != nil) { return _managedObjectContext; } _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType]; _managedObjectContext.parentContext = [self writerManagedObjectContext]; return _managedObjectContext;}// Parent context- (NSManagedObjectContext *)writerManagedObjectContext{ if (_writerManagedObjectContext != nil) { return _writerManagedObjectContext; } NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { _writerManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType: NSPrivateQueueConcurrencyType]; [_writerManagedObjectContext setPersistentStoreCoordinator:coordinator]; } return _writerManagedObjectContext;}
  • 44. Parent Child Context__block NSManagedObjectContext *writerObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] writerManagedObjectContext];__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];__block NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ // // Do lots of async work here // [temporaryContext save:&error]; {abort();} // Save the context. [managedObjectContext performBlock:^{ [managedObjectContext save:&error]; {abort();} // Save the context. [writerObjectContext performBlock:^{ [writerObjectContext save:&error]; {abort();} // Save the context. }]; // writer }]; // main}]; // temp context
  • 45. Parent Child Context__block NSManagedObjectContext *writerObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] writerManagedObjectContext];__block NSManagedObjectContext *managedObjectContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];__block NSManagedObjectContext *temporaryContext = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType];temporaryContext.parentContext = managedObjectContext;[temporaryContext performBlock:^{ NSPrivateQueueConcurrencyType // // Do lots of async work here // NSMainQueueConcurrency [temporaryContext save:&error]; {abort();} // Save the context. [managedObjectContext performBlock:^{ [managedObjectContext save:&error]; {abort();} // Save the context. [writerObjectContext performBlock:^{ [writerObjectContext save:&error]; {abort();} // Save the context. }]; // writer }]; // main}]; // temp context
  • 46. Asynchronous Saving - Parent Child Context Code Example https://github.com/mmorey/CoreDataMultiContext/tree/parent-context
  • 47. Still Blocking?
  • 48. Still Blocking?Small and frequent saves during import
  • 49. Still Blocking?Wait for opportunity when user won’t notice
  • 50. Still Blocking?- (void)setStalenessInterval:(NSTimeInterval)expiration
  • 51. Still Blocking? NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequestmanagedObjectContext:self.managedObjectContext sectionNameKeyPath:@"sections" cacheName:@"default-cache"];
  • 52. Still Blocking? For VERY LARGE amounts of data it may be better to generate the SQLite file on theserver, download it asynchronously, and set it up as an additional persistent store.
  • 53. References Nested MOC Release Notes: http://developer.apple.com/library/mac/#releasenotes/DataManagement/RN-CoreData/index.html Core Data Programming Guide:http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/CoreData/cdProgrammingGuide.html Cocoanetics Blog: http://www.cocoanetics.com/2012/07/multi-context-coredata/ http://www.cocoanetics.com/2013/02/zarra-on-locking/
  • 54. Thanks! Questions? Get in Touch. Twitter: @xzolian App.net: @morey Email: matt@matthewmorey.com URL: http://matthewmorey.com

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