Indeed, but the pthreads in my example were created as detached (I showed a parameter '&detach' which was intended to give a strong hint to that effect).

And I agree that pthread_kill has to be used with caution, but in my case the threads were all 'sleep'ing, so I killed them with SIGALRM and they woke up and proceeded on their way, which was to kill themselves.

But you have not answered my main question, which was what happens (or is supposed to happen) if you create another thread on the same tid variable before it has died. It may be (indeed probably is) bad practice, but bad practice (aka s**t) happens, and the pthread system offers no help in avoiding it.

And if I need to know whether the thread on some tid is still running, how can I tell? Do I have to create some sufficiently global variable and keep track of it myself (which is what I have done) is is there some way I can ask?

It seems that what I need to do is discover whether a thread is still running on the tid, and then either arrane to kill it, or else to persuade the existing thread to take on new responsibilities. When I first wrote this code, I did not consider this possibility and it worked fine until things started to happen too faat.