Is NSUserDefault thread safe?

Question

https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSUserDefaults_Class/Reference/Reference.html says it is

...shou

Answer 1

Speaking for 10.10 and iOS8 if you looking into the implementation you'll find that -[NSUserDefaults setObject:forKey:] is calling __CFPreferencesSetAppValueWithContainer, which will eventually end up in +[CFPrefsSource withSourceForIdentifier:user:byHost:container:perform:]. This method is using a pthread_mutex_t to lock the access to the dictionary containing the values.

So NSUserDefaults is thread safe.