Could someone explain 'CoreAnimation: timed out fence' log message?

I received a report of a crash with our iPad application, with a log message attached. The last couple of lines of the log message are as follows:

Aug 21 08:58:51 2TesterPad backboardd[26] <Warning>: CoreAnimation: timed out fence 25993
Aug 21 08:58:51 2TesterPad backboardd[26] <Warning>: CoreAnimation: updates deferred for too long
Aug 21 08:58:52 2TesterPad AppName[2428] <Warning>: CoreAnimation: failed to receive fence reply: 10004003

Can anyone tell me what these log messages mean please? I've been unable to find any good information about this online.

Solution

It typically means that core animation operations are queued, but have been pending for too long and have timed out.

A few things to check:

Ensure you are calling the super method on any -viewDidAppear and -viewWillAppear
Ensure you are not performing animations before the view is presented via -viewDidAppear
Check you are only interacting with the UI on the main thread. I've seen issues with wait fence message when displaying a UIAlertView when the relevant code was executed on a background thread. You can make sure by putting your code in a block and sending it to the main thread, example below
This can happen if you have a UIScollView that has a lot of subviews and you animate the UIScrollView. In this case it will animate all of its subviews, even if those subviews aren't on screen. See this answer: https://stackoverflow.com/a/10938889/257550 . One solution to fix this would be to redesign the view to use a UITableView which ensures that only the subviews in the visible cells are animated.
```
dispatch_async(dispatch_get_main_queue(), ^{

    UIAlertView *alert = 
       [[UIAlertView alloc] initWithTitle:@"title", 
                                   mssage:@"message"
                                 delegate:nil 
                        cancelButtonTitle:@"OK"
                        otherButtonTitles:nil];

    [alert show];
});
```