@fmurphy: indeed, but from that same page:
Note that pthread_kill() only causes the signal to be handled in the context of the given thread; the signal action (termination or stopping) affects the process as a whole.
What I meant to say was that a signal sent from outside the process eg
kill -SIGHUP <pid of process>
cannot be specified to target a given thread; it's delivered to the process as a whole and the actual thread that will first respond is undefined.