Awww. I just encountered another problem with that. Since these threads are threads and not forks, there are no PIDs, I could use to identify the thread (I would have used that PIDs in the above named shared hash with thread state etc.). Is there some ID for threads? I know I could use the object itself as key in the hash since I can retrieve it in child via threads->self(). But it if should be something, that is not recycled so fast. I mean if the thread is finished I need to depend on no new thread by coincidence gets the same "ID" before the parent gets a chance to check the hash for the status and returns. This should never take longer than lets say worst case a few seconds (more likely ms) so PIDs where a nice ID for that job.