interprocess mutex

[Janne Hellsten <janne@hybrid.fi>]

Hello,

I need to sequentialize two processes accessing the same GDBM database 
(OCaml's dbm library).  Since GDBM allows for only one writer at a time, 
I need a way to block until the previous writer has finished.  I think 
there is a way to do this with the original GDBM library since it claims 
to handle the file lockings properly -- I could block based on the 
returned error codes.  However, this functionality does not appear to be 
exposed through the Dbm module.

Of course I can implement this blocking myself with an interprocess 
mutex.  But how can I implement such a mutex in OCaml?  I couldn't find 
anything from the standard library that would resemble my problem.

Is it easily doable or do I need to go and start hacking C code?  I've 
never done it on Unix but I know it's easily done on Windows.

Thanks in advance,
Janne

P.S.  I'm using GDBM merely as a cache between process invocations, so 
using a more heavyweight DB is out of the question.