I wonder whether the intermittent failures I have seen on tests runtime008, thread015 and thread020 (all of which are supposedly fixed) might be due to one of the thread-related bugs I reported some time ago. In particular, these three, which have not been closed yet, may be relevant: 14519 Blocking C externals that can raise exception not thread-safe 14518 Routine {THREAD_CONTROL}.join not thread-safe 14517 Possible execution of `eif_thr_exit' and call to eif_access while GC in progress Just a thought.