Thank you for the pointer. I understand that the document describes the only correct way to use LWLock in extensions and using LWLockRegisterTranche is a non-standard or prohibit way to do that.
By the way, in the case of orafce, it uses LWLockRegisterTranche directly but only when !found. So if any backend other than the creator of the shmem want to access tranche, the puch tranche is not found on the process and crashes. I think this is it.
If no other modules is installed, registeriing a tranche even if found will supress the crash but it is not a solution at all.
At least for 9.6 or 10, orafce should do that following the documentation. But it still can crash from the problem by the separate NamedLWLockTrancheArray. (ID range check in LWLockInitialize would be useless if it is not used by extensions)
