Thanks.  Maybe someone on the list has some experience and
could contribute some advice...

What I have is a long-running ocaml thread, invoked from Objc,
and I would like to have other Objc threads running that
report on the progress of the ocaml thread, etc.  That means
communication between the ocaml thread and the Objc threads,
which I now know cannot occur using most functions of the
ocaml C api.

So any advice on the best way to communicate between these
threads?

I am guessing I need to having locking implemented in Objc
and exported to ocaml, then both the ocaml thread and the
Objc threads can synchronize.  Then I can for example
allocate a buffer in Objc and export it to ocaml and the
threads can communicate over the buffer using the locking
as necessary.  Or this might be packaged up a bit more
nicely, but the locking and storage must be done on the
Objc side.

-Trevor