\fBPAPI_unregister_thread\fP should be called when the user wants to shutdown a particular thread and free the associated thread ID\&. THIS IS IMPORTANT IF YOUR THREAD LIBRARY REUSES THE SAME THREAD ID FOR A NEW KERNEL LWP\&. OpenMP does this\&. OpenMP parallel regions, if separated by a call to omp_set_num_threads() will often kill off the underlying kernel LWPs and then start new ones for the next region\&. However, omp_get_thread_id() does not reflect this, as the thread IDs for the new LWPs will be the same as the old LWPs\&. PAPI needs to know that the underlying LWP has changed so it can set up the counters for that new thread\&. This is accomplished by calling this function\&.