我有一个单例类,它使用GCD(Grand Central Dispatch)队列在后台将JSON对象保存到CoreData数据库。这在大多数情况下都是完美的,但在iPad 2和iPad Mini设备上,我遇到了一些过程冻结的问题。
我的设置很简单。我有一个后台调度队列(backgroundQueue)设置为串行运行,我有一个单独的NSManagedObjectContext实例用于后台队列。当我想将某些内容保存到数据库时,我调用了开始保存过程的方法,在该方法中,我使用dispatch_async在后台线程上调用我的保存逻辑。
一旦所有处理逻辑都已运行,我保存后台MOC,并使用NSManagedObjectContextDidSaveNotification将更改从后台MOC合并到主线程MOC。后台线程等待此操作完成,一旦完成,它将运行队列中的下一个块,如果有的话。以下是我的代码。
dispatch_queue_t backgroundQueue;
- (id)init
{
if (self = [super init])
{
// init the background queue
backgroundQueue = dispatch_queue_create(VS_CORE_DATA_MANAGER_BACKGROUND_QUEUE_NAME, DISPATCH_QUEUE_SERIAL);
}
return self;
}
- (void)saveJsonObjects:(NSDictionary *)jsonDict
objectMapping:(VS_ObjectMapping *)objectMapping
class:(__unsafe_unretained Class)managedObjectClass
completion:(void (^)(NSArray *objects, NSError *error))completion
{
[VS_Log logDebug:@"**** Queue Save JSON Objects for Class: %@", managedObjectClass];
// process in the background queue
dispatch_async(backgroundQueue, ^(void)
{
[VS_Log logDebug:@"**** Dispatch Save JSON Objects for Class: %@", managedObjectClass];
// create a new process object and add it to the dictionary
currentRequest = [[VS_CoreDataRequest alloc] init];
// set the thead name
NSThread *currentThread = [NSThread currentThread];
[currentThread setName:VS_CORE_DATA_MANAGER_BACKGROUND_THREAD_NAME];
// if there is not already a background context, then create one
if (!_backgroundQueueManagedObjectContext)
{
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
// create the background queue
_backgroundQueueManagedObjectContext = [[NSManagedObjectContext alloc] init];
[_backgroundQueueManagedObjectContext setPersistentStoreCoordinator:coordinator];
[_backgroundQueueManagedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
_backgroundQueueManagedObjectContext.undoManager = nil;
// listen for the merge changes from context did save notification on the background queue
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeChangesFromBackground:) name:NSManagedObjectContextDidSaveNotification object:_backgroundQueueManagedObjectContext];
}
}
// save the JSON dictionary
NSArray *objects = [self saveJSON:jsonDict objectMapping:objectMapping class:managedObjectClass managedObjectContext:_backgroundQueueManagedObjectContext level:0];
// save the objects so we can access them later to be re-fetched and returned on the main thread
if (objects.count > 0)
[currentRequest.objects addObjectsFromArray:objects];
// save the object IDs and the completion block to global variables so we can access them after the save
if (completion)
currentRequest.completionBlock = completion;
[VS_Log logDebug:@"**** Save MOC for Class: %@", managedObjectClass];
// save all changes object context
[self saveManagedObjectContext];
});
}
- (void)mergeChangesFromBackground:(NSNotification *)notification
{
[VS_Log logDebug:@"**** Merge Changes From Background"];
// save the current request to a local var since we're about to be processing it on the main thread
__block VS_CoreDataRequest *request = (VS_CoreDataRequest *)[currentRequest copy];
__block NSNotification *bNotification = (NSNotification *)[notification copy];
// clear out the request
currentRequest = nil;
dispatch_sync(dispatch_get_main_queue(), ^(void)
{
[VS_Log logDebug:@"**** Start Merge Changes On Main Thread"];
// merge changes to the primary context, and wait for the action to complete on the main thread
[_managedObjectContext mergeChangesFromContextDidSaveNotification:bNotification];
NSMutableArray *objects = [[NSMutableArray alloc] init];
// iterate through the updated objects and find them in the main thread MOC
for (NSManagedObject *object in request.objects)
{
NSError *error;
NSManagedObject *obj = [[self managedObjectContext] existingObjectWithID:object.objectID error:&error];
if (error)
[self logError:error];
if (obj)
[objects addObject:obj];
}
// call the completion block
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(objects, nil);
}
[VS_Log logDebug:@"**** Complete Merge Changes On Main Thread"];
// clear the request
request = nil;
});
[VS_Log logDebug:@"**** Complete Merge Changes From Background"];
}
当问题发生时,一切似乎运行正常,它进入mergeChangesFromBackground:方法,但不调用dispatch_async()。
正如我上面提到的,代码在大多数情况下运行完美。只有当我在iPad 2或iPad Mini上测试并保存大型物体时才会出现问题。
有没有人知道为什么会这样?
由于
**编辑**
自写这篇文章以来,我已经了解了嵌套的NSManagedObjectContexts。我修改了我的代码以使用它,它似乎运行良好。但是,我仍然有同样的问题。思考?另外,对嵌套MOC的任何评论?
- (void)saveJsonObjects:(NSDictionary *)jsonDict
objectMapping:(VS_ObjectMapping *)objectMapping
class:(__unsafe_unretained Class)managedObjectClass
completion:(void (^)(NSArray *objects, NSError *error))completion
{
// process in the background queue
dispatch_async(backgroundQueue, ^(void)
{
// create a new process object and add it to the dictionary
__block VS_CoreDataRequest *currentRequest = [[VS_CoreDataRequest alloc] init];
// set the thead name
NSThread *currentThread = [NSThread currentThread];
[currentThread setName:VS_CORE_DATA_MANAGER_BACKGROUND_THREAD_NAME];
// if there is not already a background context, then create one
if (!_backgroundQueueManagedObjectContext)
{
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
// create the background queue
_backgroundQueueManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_backgroundQueueManagedObjectContext setParentContext:[self managedObjectContext]];
[_backgroundQueueManagedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
_backgroundQueueManagedObjectContext.undoManager = nil;
}
}
// save the JSON dictionary starting at the upper most level of the key path
NSArray *objects = [self saveJSON:jsonDict objectMapping:objectMapping class:managedObjectClass managedObjectContext:_backgroundQueueManagedObjectContext level:0];
// if no objects were processed, then return with an error
if (!objects || objects.count == 0)
{
currentRequest = nil;
// dispatch the completion block
dispatch_async(dispatch_get_main_queue(), ^(void)
{
NSError *error = [self createErrorWithErrorCode:100 description:@"No objects were found for the object mapping"];
[self logMessage:error.debugDescription];
completion(nil, error);
});
}
// save the objects so we can access them later to be re-fetched and returned on the main thread
if (objects.count > 0)
[currentRequest.objects addObjectsFromArray:objects];
// save the object IDs and the completion block to global variables so we can access them after the save
if (completion)
currentRequest.completionBlock = completion;
// save all changes object context
NSError *error = nil;
[_backgroundQueueManagedObjectContext save:&error];
if (error)
[VS_Log logError:error.localizedDescription];
dispatch_sync(dispatch_get_main_queue(), ^(void)
{
NSMutableArray *objects = [[NSMutableArray alloc] init];
// iterate through the updated objects and find them in the main thread MOC
for (NSManagedObject *object in currentRequest.objects)
{
NSError *error;
NSManagedObject *obj = [[self managedObjectContext] existingObjectWithID:object.objectID error:&error];
if (error)
[self logError:error];
if (obj)
[objects addObject:obj];
}
// call the completion block
if (currentRequest.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = currentRequest.completionBlock;
saveCompletionBlock(objects, nil);
}
});
// clear out the request
currentRequest = nil;
});
}
**编辑**
大家好,
我首先要感谢大家对此的意见,因为这是我找到问题解决方案的原因。长话短说,我完全放弃了使用GCD和自定义后台队列,而现在使用嵌套上下文和“performBlock”方法来执行后台线程上的所有保存。这很有效,我提出了挂断问题。
但是,我现在有一个新的bug。每当我第一次运行我的应用程序时,每当我尝试保存具有子对象关系的对象时,我都会遇到以下异常。
-_ referenceData64仅为抽象类定义。定义 - [NSTemporaryObjectID_default _referenceData64]!
以下是我的新代码。
- (void)saveJsonObjects:(NSDictionary *)jsonDict
objectMapping:(VS_ObjectMapping *)objectMapping
class:(__unsafe_unretained Class)managedObjectClass
completion:(void (^)(NSArray *objects, NSError *error))completion
{
[_backgroundManagedObjectContext performBlock:^(void)
{
// create a new process object and add it to the dictionary
VS_CoreDataRequest *currentRequest = [[VS_CoreDataRequest alloc] init];
currentRequest.managedObjectClass = managedObjectClass;
// save the JSON dictionary starting at the upper most level of the key path
NSArray *objects = [self saveJSON:jsonDict objectMapping:objectMapping class:managedObjectClass managedObjectContext:_backgroundManagedObjectContext level:0];
if (objects.count == 0)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:@"No objects were found for the object mapping"];
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
}
else
{
// save the objects so we can access them later to be re-fetched and returned on the main thread
[currentRequest.objects addObjectsFromArray:objects];
// save the object IDs and the completion block to global variables so we can access them after the save
currentRequest.completionBlock = completion;
[_backgroundManagedObjectContext lock];
@try
{
[_backgroundManagedObjectContext processPendingChanges];
[_backgroundManagedObjectContext save:nil];
}
@catch (NSException *exception)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:exception.reason];
}
[_backgroundManagedObjectContext unlock];
// complete the process on the main thread
if (currentRequest.error)
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
else
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidSucceed:) withObject:currentRequest waitUntilDone:NO];
// clear out the request
currentRequest = nil;
}
}];
}
- (void)backgroundSaveProcessDidFail:(VS_CoreDataRequest *)request
{
if (request.error)
[self logError:request.error];
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(nil, request.error);
}
}
- (void)backgroundSaveProcessDidSucceed:(VS_CoreDataRequest *)request
{
// get objects from main thread
NSArray *objects = nil;
if (request.objects.count > 0)
{
NSFetchRequest *fetchReq = [NSFetchRequest fetchRequestWithEntityName:[NSString stringWithFormat:@"%@", request.managedObjectClass]];
fetchReq.predicate = [NSPredicate predicateWithFormat:@"self IN %@", request.objects];
objects = [self executeFetchRequest:fetchReq];
}
// call the completion block
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(objects, nil);
}
}
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
// create the MOC for the backgroumd thread
_backgroundManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_backgroundManagedObjectContext setPersistentStoreCoordinator:coordinator];
[_backgroundManagedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
_backgroundManagedObjectContext.undoManager = nil;
// create the MOC for the main thread
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setParentContext:_backgroundManagedObjectContext];
[_managedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
}
return _managedObjectContext;
}
你们有没有人知道为什么会发生这起事故?
答案 0 :(得分:2)
您可能想要考虑这种上下文架构(未经测试的代码):
mainManagedObjectContext将以相同的方式初始化,但使用NSMainQueueConcurrencyType
并且没有观察者(顺便说一句,请记住删除您的观察者)
- (void) mergeChangesFromBackground:(NSNotification*)notification
{
__block __weak NSManagedObjectContext* context = self.managedObjectContext;
[context performBlockAndWait:^{
[context mergeChangesFromContextDidSaveNotification:notification];
}];
}
- (NSManagedObjectContext*) bgContext
{
if (_bgContext) {
return _bgContext;
}
NSPersistentStoreCoordinator* coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_bgContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_bgContext setPersistentStoreCoordinator:coordinator];
[_bgContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
[_bgContext setUndoManager:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(mergeChangesFromBackground:)
name:NSManagedObjectContextDidSaveNotification
object:_bgContext];
return _bgContext;
}
- (void) doSomethingOnBGContextWithoutBlocking:(void(^)(NSManagedObjectContext*))contextBlock
{
__block __weak NSManagedObjectContext* context = [self bgContext];
[context performBlock:^{
NSThread *currentThread = [NSThread currentThread];
NSString* prevName = [currentThread name];
[currentThread setName:@"BGContextThread"];
contextBlock(context);
[context reset];
[currentThread setName:prevName];
}];
}
答案 1 :(得分:0)
我首先要感谢大家对此的意见,因为这是我找到问题解决方案的原因。长话短说,我完全放弃了使用GCD和自定义后台队列,而现在使用嵌套上下文和“performBlock”方法来执行后台线程上的所有保存。这很有效,我提出了挂断问题。
但是,我现在有一个新的bug。每当我第一次运行我的应用程序时,每当我尝试保存具有子对象关系的对象时,我都会遇到以下异常。
-_ referenceData64仅为抽象类定义。定义 - [NSTemporaryObjectID_default _referenceData64]!
以下是我的新代码。
- (void)saveJsonObjects:(NSDictionary *)jsonDict
objectMapping:(VS_ObjectMapping *)objectMapping
class:(__unsafe_unretained Class)managedObjectClass
completion:(void (^)(NSArray *objects, NSError *error))completion
{
[_backgroundManagedObjectContext performBlock:^(void)
{
// create a new process object and add it to the dictionary
VS_CoreDataRequest *currentRequest = [[VS_CoreDataRequest alloc] init];
currentRequest.managedObjectClass = managedObjectClass;
// save the JSON dictionary starting at the upper most level of the key path
NSArray *objects = [self saveJSON:jsonDict objectMapping:objectMapping class:managedObjectClass managedObjectContext:_backgroundManagedObjectContext level:0];
if (objects.count == 0)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:@"No objects were found for the object mapping"];
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
}
else
{
// save the objects so we can access them later to be re-fetched and returned on the main thread
[currentRequest.objects addObjectsFromArray:objects];
// save the object IDs and the completion block to global variables so we can access them after the save
currentRequest.completionBlock = completion;
[_backgroundManagedObjectContext lock];
@try
{
[_backgroundManagedObjectContext processPendingChanges];
[_backgroundManagedObjectContext save:nil];
}
@catch (NSException *exception)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:exception.reason];
}
[_backgroundManagedObjectContext unlock];
// complete the process on the main thread
if (currentRequest.error)
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
else
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidSucceed:) withObject:currentRequest waitUntilDone:NO];
// clear out the request
currentRequest = nil;
}
}];
}
- (void)backgroundSaveProcessDidFail:(VS_CoreDataRequest *)request
{
if (request.error)
[self logError:request.error];
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(nil, request.error);
}
}
- (void)backgroundSaveProcessDidSucceed:(VS_CoreDataRequest *)request
{
// get objects from main thread
NSArray *objects = nil;
if (request.objects.count > 0)
{
NSFetchRequest *fetchReq = [NSFetchRequest fetchRequestWithEntityName:[NSString stringWithFormat:@"%@", request.managedObjectClass]];
fetchReq.predicate = [NSPredicate predicateWithFormat:@"self IN %@", request.objects];
objects = [self executeFetchRequest:fetchReq];
}
// call the completion block
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(objects, nil);
}
}
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
// create the MOC for the backgroumd thread
_backgroundManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_backgroundManagedObjectContext setPersistentStoreCoordinator:coordinator];
[_backgroundManagedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
_backgroundManagedObjectContext.undoManager = nil;
// create the MOC for the main thread
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setParentContext:_backgroundManagedObjectContext];
[_managedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
}
return _managedObjectContext;
}
你们有没有人知道为什么会发生这起事故?
**编辑**
女士们和男士们我找到了解决方案。显然,即使使用嵌套上下文,您仍然必须通过NSManagedObjectContextDidSaveNotification合并更改。一旦我将其添加到我的代码中,它们就开始完美地工作了。以下是我的工作代码。万分感谢!
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil)
return _managedObjectContext;
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil)
{
// create the MOC for the backgroumd thread
_backgroundManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_backgroundManagedObjectContext setPersistentStoreCoordinator:coordinator];
[_backgroundManagedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
_backgroundManagedObjectContext.undoManager = nil;
// create the MOC for the main thread
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setParentContext:_backgroundManagedObjectContext];
[_managedObjectContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeChangesFromContextDidSaveNotification:) name:NSManagedObjectContextDidSaveNotification object:_backgroundManagedObjectContext];
}
return _managedObjectContext;
}
- (void)saveJsonObjects:(NSDictionary *)jsonDict
objectMapping:(VS_ObjectMapping *)objectMapping
class:(__unsafe_unretained Class)managedObjectClass
completion:(void (^)(NSArray *objects, NSError *error))completion
{
// perform save on background thread
[_backgroundManagedObjectContext performBlock:^(void)
{
// create a new process object and add it to the dictionary
VS_CoreDataRequest *currentRequest = [[VS_CoreDataRequest alloc] init];
currentRequest.managedObjectClass = managedObjectClass;
// save the JSON dictionary starting at the upper most level of the key path
NSArray *objects = [self saveJSON:jsonDict objectMapping:objectMapping class:managedObjectClass managedObjectContext:_backgroundManagedObjectContext level:0];
if (objects.count == 0)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:@"No objects were found for the object mapping"];
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
}
else
{
// save the objects so we can access them later to be re-fetched and returned on the main thread
[currentRequest.objects addObjectsFromArray:objects];
// save the object IDs and the completion block to global variables so we can access them after the save
currentRequest.completionBlock = completion;
[_backgroundManagedObjectContext lock];
@try
{
[_backgroundManagedObjectContext processPendingChanges];
[_backgroundManagedObjectContext save:nil];
}
@catch (NSException *exception)
{
currentRequest.error = [self createErrorWithErrorCode:100 description:exception.reason];
}
[_backgroundManagedObjectContext unlock];
// complete the process on the main thread
if (currentRequest.error)
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidFail:) withObject:currentRequest waitUntilDone:NO];
else
[self performSelectorOnMainThread:@selector(backgroundSaveProcessDidSucceed:) withObject:currentRequest waitUntilDone:NO];
// clear out the request
currentRequest = nil;
}
}];
}
- (void)mergeChangesFromContextDidSaveNotification:(NSNotification *)notification
{
[_managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
}
- (void)backgroundSaveProcessDidFail:(VS_CoreDataRequest *)request
{
if (request.error)
[self logError:request.error];
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(nil, request.error);
}
}
- (void)backgroundSaveProcessDidSucceed:(VS_CoreDataRequest *)request
{
// get objects from main thread
NSArray *objects = nil;
if (request.objects.count > 0)
{
NSFetchRequest *fetchReq = [NSFetchRequest fetchRequestWithEntityName:[NSString stringWithFormat:@"%@", request.managedObjectClass]];
fetchReq.predicate = [NSPredicate predicateWithFormat:@"self IN %@", request.objects];
objects = [self executeFetchRequest:fetchReq];
}
// call the completion block
if (request.completionBlock)
{
void (^saveCompletionBlock)(NSArray *, NSError *) = request.completionBlock;
saveCompletionBlock(objects, nil);
}
}