boost::thread IDs

I know there was a discussion about the need for these and why they're not in the library. I can't find it, however. I'm having the same problem the original poster had: I'm using the thread ID as an identifier in a data structure (std::map in this case). Now that I'm converting to the Boost threads library, I have to change that. I'm not sure what to do instead. Any help, either a pointer to the original discussion or direct suggestions, will be much appreciated. Thanks, - Mark P.S. Other than this glitch, my ObjectSpace Toolkit removal has been painless. Great libraries!