[JdeBP]

The Windows NT model built on operating systems design thought that happened in the 1980s, that took far too many years to trickle into the other operating systems whose designs such thought was looking at.

However, FreeBSD has had process descriptors since roughly 2010. They have the slightly odd semantics of terminating processes when all descriptors to them are closed. But they can be used as descriptors with kqueue() and the like.