implementing NSUserDefaults Synchronization in a Multithreaded Environment on Objective-C
I've tried everything I can think of but I'm deploying to production and After trying multiple solutions online, I still can't figure this out..... I'm working with an scenario with `NSUserDefaults` not properly synchronizing values when accessed from multiple threads in my Objective-C application. The app is built using Xcode 14.0 and targets iOS 15. I have a scenario where I write user settings in the background thread and read them on the main thread, but it seems like the main thread is sometimes accessing stale data, particularly after writing. Here's a simplified version of what I'm doing: In my background thread, I'm saving the data like this: ```objective-c dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ [[NSUserDefaults standardUserDefaults] setObject:@"newValue" forKey:@"myKey"]; [[NSUserDefaults standardUserDefaults] synchronize]; }); ``` Then, on the main thread, I read the value as follows: ```objective-c NSString *value = [[NSUserDefaults standardUserDefaults] objectForKey:@"myKey"]; NSLog(@"Value: %@", value); ``` The scenario arises when a user changes the setting frequently, and I notice that sometimes the logged value is not reflecting the latest change, even after calling `synchronize`. I've even tried using a lock to ensure only one thread can access `NSUserDefaults` at a time: ```objective-c @ synchronized(self) { // reading and writing code here } ``` However, the question continues, and Iām still seeing the old value in the logs. Are there any best practices for using `NSUserDefaults` across multiple threads? Is there something Iām missing in how `synchronize` works, or should I consider using a different method for saving user settings that require immediate consistency across threads? For context: I'm using Objective-C on Linux. Any help would be greatly appreciated! Thanks for your help in advance! I'm coming from a different tech stack and learning Objective-C. Thanks in advance! The project is a CLI tool built with Objective-C. This issue appeared after updating to Objective-C LTS. Is there a better approach?