ProcSignalSlot vs. PGPROC

Markus Wanner <markus@bluegap.ch> writes:

do I understand correctly that a BackendId is just an index into the
ProcSignalSlots array and not (necessarily) the same as the index into
ProcArrayStruct's procs?

If yes, could these be synchronized? Why is ProcSignalSlot not part of
PGPROC at all? Both are shared memory structures per backend (plus
NUM_AUXILIARY_PROCS). What am I missing?

It's easier to keep those modules separate. I believe also that there
are (or could be) processes that have entries in one array but not the
other.

regards, tom lane