what's role of 'extract' of structure Objects_Information's member?

[Bacon Xu]

I have studied all of document of RTEMS, and now, I start to read
source code of RTEMS. When to see the structure Objects_Information,
I'm very confused about 'extract'. it's a function pointer, there is
initialized codes in _Objects_Initialize_information under
multiprocessing situations. But I haven't found any place to use this
field. What is  role of  the 'extract' ?

--
BRs
Bacon
baconxu at gmail.com    An amateur of RTEMS.