NSThread Comparisons

[Justin Kendrick]

I'm writing a class which needs to determine the current thread and  
get an object tied to that thread.  I'd like to use an NSDictionary  
keyed by an NSThread object, but NSThread instances not copyable (and  
I can't find any good documentation on how NSDictionary matches non- 
NSString keys anyway).  Beyond that, I thought that I might use an  
NSValue created with valueWithUnretainedObject:, but that feels really  
hackish.

For that matter, is there a one-to-one mapping between NSThread  
instances and Posix threads -- that is, can I compare two NSThread  
pointers and conclude that the NSThread instances do or do not  
represent the same thread?