Re: [9fans] stack reclamation on Unix using clone, rfork_thread, etc.

[Richard C Bilson <rcbilson@plg2.math.uwaterloo.ca>]

> From: Philippe Anel <xigh@free.fr> Fri Jun  4 12:23:49 2004
> 
> void
> exit_thread()
>   {
>          struct segment * s;
> 
>          lock(&addrspace);
>          for (s = addrspace.tofree; s; s = s->next)
>                  free(s->addr);
>          if (--refcount) {
>                  s = find_segment_from_id(get_my_thread_id());
>                  list_remove(s);
>                  list_add(tofree, s);
>          }
>          unlock(&addrspace);
> }
> 
> ------------------------------------------------------------------------------
> 
> It would free the stack of the previous exited thread.

This isn't actually so different from what Russ describes -- you're just
keeping a separate free list, rather than setting a per-thread flag in
some global list of all threads.

Note that you have to be very careful about race conditions -- your
stack could disappear immediately after the call to unlock, which means
that you'd better be done all you need to do at that point, except for
calling _exit (and even that is problematic).