crash with -com.apple.CoreData.ConcurrencyDebug 1 when fetching entites

[JanC]

Hi,
every time I fetch and access a NSManagedObject in a background thread with -com.apple.CoreData.ConcurrencyDebug 1, I get a crash. It is reproducible with:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    PSPlayer *player = [[PSPlayer MR_findAll] firstObject];
    NSLog(@"player = %@", player.name);
});

I'm using 2.3.0 beta 5

[Alydyn]

Thats because you are fetching in background without specifying a context. -MR_findAll uses MR_contextForCurrentThread which is no longer recommended.
Try this:

NSManagedObjectContext *context = [NSManagedObjectContext MR_context];
[context performBlock:^{
    PSPlayer *player = [[PSPlayer MR_findAllInContext:context] firstObject];
    NSLog(@"player = %@", player.name);
}];

[JanC]

ok, I see. I thought that all the methods described in the docs were guaranteeing to use the appropriate context. Also, I have to surround the access with [context performBlock:^{ ... so the docs are not yet updated for 2.3, correct?

[JanC]

Now, how come I have the crash when calling this in a main method of a NSOperation ?

- (void)main
{
    @autoreleasepool {
        NSManagedObjectContext *context = [NSManagedObjectContext MR_context];
        PSPlayer *player = (PSPlayer *) [context objectWithID:self.playerId];
        NSLog(@"name = %@", player.name);
        // rest  of NSOperation logic
    }
}

Do I have to wrap the entire logic of the NSOperation in performBlockAndWait

- (void)main
{
    @autoreleasepool {

        __block BOOL keepUpdating = YES;

        __block PSPlayer *player;
        NSManagedObjectContext *context = [NSManagedObjectContext MR_context];
        [context performBlockAndWait:^{
            player = (PSPlayer *) [context objectWithID:self.playerId];
            NSLog(@"name = %@", player.name);
            // rest  of NSOperation logic
        }];
    }
}

[Alydyn]

NSOperation's -main method will almost certainly be called on a different thread than -start for concurrent operations. First, try creating the context in -start. And then, yes, you will need to wrap access in -performBlockAndWait:
An excellent write up is on objc.io

[JanC]

ok thanks. objc.io is my Bible but it looks like I should read it more often. cheers