unw_cursor_t thread safety

[Vox Flores]

Hi libunwind-devel,

I am looking for clarification about libunwind (3). 

unw_cursor_t cursor
unw_init_remote(&cursor, as, upt);
unw_cursor_t old_cursor = cursor;
unw_step(&cursor)


After calling unw_step(), is it safe to use `cursor` and `old_cursor` in 
separate threads? unw_cursor_t is an opaque type, so it's not clear if 
unw_step() creates a new cursor that is distinct from old_cursor.

Thanks!

--
vox