> But ForkingPickler could be used in multiprocessing.connection,
> couldn't it?

I suppose so.

Note that the way a connection handle is transferred between existing processes is unnecessarily inefficient on Windows.  A background server thread (one per process) has to be started and the receiving process must connect back to the sending process to receive its duplicate handle.

There is a simpler way to do this on Windows.  The sending process duplicates the handle, and the receiving process duplicates that second handle using DuplicateHandle() and the DUPLICATE_CLOSE_SOURCE flag.  That way no server thread is necessary on Windows.

I got this to work recently for pickling references to file handles for mmaps on.  (A server thread would still be necessary on Unix.)