核心数据管理上下文不保存在多线程环境中 [英] Core Data Managed Context not saving in multi-threaded environment
问题描述
在尝试了解有关Core Data和多线程的更多信息时，我写了一个无法保存到核心数据的应用程序。首先一些
的背景。在我的视图出现之前，我创建托管上下文。这发生在
主线程：
While trying to learn more about Core Data and multithreading, I wrote an app that fails to save to core data. First some background. Before my view appears, I create managed context. This happens in the main thread:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if (!self.managedObjectContext) [self useDocument];
}
- (void)useDocument
{
NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
url = [url URLByAppendingPathComponent:MY_DOCUMENT];
UIManagedDocument *document = [[UIManagedDocument alloc] initWithFileURL:url];
if (![[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
[document saveToURL:url
forSaveOperation:UIDocumentSaveForCreating
completionHandler:^(BOOL success) {
if (success) {
NSLog(@"@@@AMRO--->managedObjectContext has been setup");
self.managedObjectContext = document.managedObjectContext;
[self refresh];
}
}];
} else if (document.documentState == UIDocumentStateClosed) {
[document openWithCompletionHandler:^(BOOL success) {
if (success) {
NSLog(@"@@@AMRO--->managedObjectContext has been opened");
self.managedObjectContext = document.managedObjectContext;
[self refresh];
}
}];
} else {
NSLog(@"@@@AMRO--->managedObjectContext has been set");
self.managedObjectContext = document.managedObjectContext;
}
}
当我的视图出现时，我从客户端提取数据使用这种方法。
的原因，我这样做是因为我不想我的视图被阻止，因为我的客户端
刷新发生：
When my view appears, I fetch data from a client using this approach. The reason I do this is because I do not want my view to be blocked as my client refresh is happening:
dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
dispatch_async(fetchQ, ^{
[self.managedObjectContext performBlock:^{
dispatch_async(dispatch_get_main_queue(), ^{
[self reload];
dispatch_async(fetchQ, ^{
[self refreshClientInformation];
});
});
}];
});
调用 refreshClientInformation ，大约需要2分钟来检索
信息，但是，我希望视图加载与任何I
有同时。以上方法阻止我
能够保存到上下文，尽管在refreshClientInformation中显式调用
[self.managedContext save：& error]
每次客户端数据更新后。 refreshPersonalClientInformations 在客户端提取线程队列中执行。
The call to refreshClientInformation, takes about 2 minutes to retrieve
information, however, I want the view to load in the meantime with whatever I
have. The above approach prevents me
from being able to save to context despite the explicit call to
[self.managedContext save:&error] in refreshClientInformation
after each client data update. refreshPersonalClientInformations executes in the "Client Fetch" thread queue.
- (void) refreshPersonalClientInformation
{
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"CLIENT"];
request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"stationId" ascending:YES]];
NSDate *twoHoursAgo = [NSDate dateWithTimeIntervalSinceNow:-2*60*60];
request.predicate = [NSPredicate predicateWithFormat:@"conditionsUpdated < %@", twoHoursAgo];
NSError *error = nil;
int counter = 0;
// Execute the fetch
NSArray *matches = [self.managedObjectContext executeFetchRequest:request error:&error];
// Check what happened in the fetch
if (!matches) { // nil means fetch failed;
NSLog(@"ERROR: Fetch failed to find CLIENT %@ in database", DEFAULT);
} else if (![matches count]) { // none found, so lets retrieve it below
return;
} else {
for (CLIENT *client in matches) {
NSDictionary *clientDict = [ClientFetcher clientInfo:client.clientId];
client.name = [clientDict[NAME] description];
client.age = [clientDict[AGE] description];
client.updated = [NSDate date];
if (![self.managedObjectContext save:&error]) {
NSLog(@"@@@@@@@@@@@@@@@@@@@@@@@@@@AMRO Unresolved error %@, %@", error, [error userInfo]);
}
//Have to rate limit requests at no more than 10 per minute.
NSLog(@"Sleeping for 6s");
sleep(6);
NSLog(@"Done sleeping for 6s");
}
}
}
我甚至试图运行通过执行以下操作保存在refreshPersonalClientInfo中：
I even tried to run the save in refreshPersonalClientInfo by doing this:
dispatch_async(dispatch_get_main_queue(), ^{
[self.managedObjectContext save:nil];
});
但这没有效果，没有检测到错误
But that did not work, no errors were detected
作为一个实验，我改变了线程调用这个当我的视图出现和我的
核心数据最终得到保存，问题是我的视图被阻止，我得到
等待很长时间而数据正在检索。另外，当我最后说，我的意思是，当我调用 [self.managedContext save：nil] 后不会发生，但几分钟后：
As an experiment I changed the thread call to this when my view appears and my
core data eventually gets saved, the problem is that my view is blocked and I have to
wait a long time while the data is getting retrieved. Also when I say eventually, I mean that it does not happen after I call [self.managedContext save:nil], but after a few minutes:
dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
dispatch_async(fetchQ, ^{
[self.managedObjectContext performBlock:^{
[self refreshPersonalClientInformation];
dispatch_async(dispatch_get_main_queue(), ^{
[self reload];
});
}];
});
有关如何在后台线程中检索我的信息的任何建议
，
Any suggestions on how I should retrieve my informaion in a background thread and be able to save the data to disk while I still leave my UI accessible?
推荐答案
您最好创建一个子上下文来执行一切在后台：
You're better to create a child context to perform everything in the background:
dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
dispatch_async(fetchQ, ^{
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
context.parentContext = self.managedObjectContext;
[context performBlock:^{
[self refreshPersonalClientInformation];
dispatch_async(dispatch_get_main_queue(), ^{
[self reload];
});
}];
});
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