plugin dev, oid to pointer map

Hi all,

i am about to begin with postgresql plugin development.
Currently i'm trying to become somewhat familiar with the postgresql sources.

Without going too deep into details about the plugin, i want to use
many Oid to pointer relations.
The pointer is a pointer to my own struct (allocated with palloc).
There will be approx. 1000 unique oid/pointer pairs.

Basically, what i want is, to be able to get the pointer to my struct by Oid.

Is there is a suitable hashmap or key-value storage solution in the pg code?
if so, please point me to the right part of the source.

thanks,
Attila Soki