Magical Record background save seems to be blocking UI

Question

I have a NSOperation that I put in a queue. The NSOperation does some long running photo processing then I save the information/meta data in core data for that photo. In the main method of my custom NSOperation class is where I execute the below block of code

-(void)main
{
    //CODE ABOVE HANDLES PHOTO PROCESSING...
    //........

    //THEN I SAVE ALL DATA BELOW LIKE SO
    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {

        Post *post = [Post createInContext:localContext];

        //set about 15 pieces of data, all strings and floats
        post.XXXX = XXXXX;
        post.DDDD = DDDDD;
        etc...
    } completion:^(BOOL success, NSError *error) {
        NSLog(@"Done saving");
    }];
}

My issue is that even with only 3 photos when it saves it really freezes my UI. I would have thought executing this in the NSOperation I would be fine.

I should add that each NSOperation processes one photo, so at times the queue could have 5-10 photos, but I would not think this would make any difference, even with just three like I said its freezing the UI.

Thank you for the help.

UPDATE:------------*--------------

I switched to version 2.2 but that seems to be blocking the UI even more...also now I'm using

-(void)main
{
    NSManagedObjectContext *localContext = [NSManagedObjectContext    contextForCurrentThread];
    //CODE BELOW HANDLES PHOTO PROCESSING...
    //........

    //THEN I SAVE ALL DATA BELOW LIKE SO
    Post *post = [Post createInContext:localContext];

    //set about 15 pieces of data, all strings and floats
    post.XXXX = XXXXX;
    post.DDDD = DDDDD;


    [localContext saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) {

    }];
}

This is all done in my NSOperation class, am I doing something wrong?

As long as the processing happens in the main thread, your ui will freeze. — mrosales, Jun 25 '13 at 18:25

score 10 · Accepted Answer · edited Dec 07 '13 at 06:19

Don't put the saveWithBlock calls in a background thread. You're effectively creating a background thread from a background thread, which, in this case, is just slowing you down. You should just be able to call saveWithBlock and it should put all your saving code in the background. However, I'm also noticed that you make all your changes in the main UI page of the code, and only call save afterward. This is the wrong usage of this method. You want to do something more like this:

[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
    Post *post = [Post createInContext:localContext];

    //photo processing
    //update post from photo processing
} completion:^(BOOL success, NSError *error) {
   //This is called when data is in the store, and is called on the main thread
}];

If you do need an NSOperation, I suggest a different pattern:

- (void) main {
   NSManagedObjectContext *localContext = [NSManagedObjectContext confinementContext];
  // Do your photo stuff here

  Post *post = [Post createInContext:localContext];
  //more stuff to update post object

  [localContext saveToPersistentStoreAndWait];

}

thanks for the help, my wacky placement of code and threads within threads seems to be the issue. I also updated to release 2.2 and that seems to have helped as well. I ended up using your suggested saveWithBlock, the NSOperation really was not needed. — inks2002, Jun 27 '13 at 14:03

score 0 · Answer 2 · answered Jun 25 '13 at 18:25

0

Be careful in how you start the operation.

[operation start]

will start the operation on the current thread, so if you call it from the main thread (which is the UI one) it will block the interface.

You should add the operation to a queue, so that it runs in background without hogging the main thread

[[NSOperationQueue new] addOperation:operation];

answered Jun 25 '13 at 18:25

Gabriele Petronella

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I am starting it like you stated above. – inks2002 Jun 25 '13 at 19:50
sorry I should have been more clear [[NSOperationQueue new] addOperation:operation]; – inks2002 Jun 25 '13 at 22:38
I switched to tag 2.2 and that seems to be even blocking the UI even worse. I will try and do some profiling, but any advice would be appreciated. Thanks! – inks2002 Jun 26 '13 at 16:26

Magical Record background save seems to be blocking UI

2 Answers2