Changes by: Jason Hickey (jyh at cs.caltech.edu)
Date: 2006-07-12 10:08:49 -0700 (Wed, 12 Jul 2006)
Revision: 9440
Log message:

      Refined locking.  When updating the .omc file:
         - First take a read lock.
         - If the item doesn't exist, release the lock, and re-lock
           with a write-lock, and check again for the item before
           creating a new one.
      Will test again on mojave2+filer.