objective-c - NSUserDefault 线程安全吗？

Question

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

...should prevent users from editing that preference by disabling any appropriate controls.

The NSUserDefaults class is thread-safe. Persistence of NSURL and file reference URLs...

这个冗长的讨论表明它不是

http://www.cocoabuilder.com/archive/cocoa/155227-nsuserdefaults-thread-safety.html

那么哪个是对的呢？还有为什么意见不同。

Answer 1

Apple iOS 5.1 和 OS X 10.7 文档说它是线程安全的；因此它是线程安全的。