- /* Cannot detach a thread that's already exiting */
- if (a_xchg(&t->exitlock, 1))
- return pthread_join(t, 0);
- t->detached = 1;
- t->exitlock = 0;
+ /* If the cas fails, detach state is either already-detached
+ * or exiting/exited, and pthread_join will trap or cleanup. */
+ if (a_cas(&t->detach_state, DT_JOINABLE, DT_DETACHED) != DT_JOINABLE)
+ return __pthread_join(t, 0);