Open Radar

 
Summary:
On iOS simulator 9.3, the UIDevice method "identifierForVendor" does not consistently return the same value if called at the beginning of the app lifetime from a background thread. If called in the background near app startup, it returns a different value then it does when called on the main thread or when called in the background at a later point in the app lifetime.

Steps to Reproduce:
1. Use the attached code in an app's AppDelegate.
2. Run on a iOS Simulator 9.3.
3. Observe the two printed values are different.

Note that the values printed will be the same if you either uncomment the sleep or run on iOS simulator <= 9.2

Expected Results:
In the simulator, vendor id should be the same on every call in a single app launch.

Actual Results:
The value returned early in the app life on a background thread is different then when called later or when called on the main thread.

attachment:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//        [NSThread sleepForTimeInterval:1];
        NSLog(@"vendor id background: %@", [[[UIDevice currentDevice] identifierForVendor] UUIDString]);
        
    });
    
    NSLog(@"vendor id: %@", [[[UIDevice currentDevice] identifierForVendor] UUIDString]);
    return YES;
}