Making modules thread-safe?

Is there anyone who could make a nice README.TSRM that goes into nice detail about how to make a module thread-safe? Neither of the Sybase modules are thread safe right now. I am willing to go through and make any changes that I can figure out, but that seems to be a rather large patch to have someone else reviewing. It might be easier if someone who knows it pretty well were to give details. There seem to be some pretty good hints in the MySQL module, but I'm not sure if there is some inherent thread safety to the MySQL libs that is not available elsewhere...I know that they use a version of MIT pthreads when compiling, but not sure how much of that PHP is taking direct advantage of? Anyways, the more of this you guys can educate me on, the more help I'll be down the road. :)