Re: Using Global Variables

[agate!spool.mu.edu!caen!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!news .sei.cmu.edu!jjs@ucbvax.Berkeley.EDU (Jeffrey Stewart)]

We are currently working with a design simulator project which will be running 
as either real-time or non real-time, depending on the site where it is 
installed.  One of the engineering goals for this simulator was to be as
run-time configurable as possible, given certain limitations of Ada.

Our approach has been to incorporate some of the concepts of OODBs, where there
is a central allocator of memory to which the objects subscribe, the objects
then receive a pointer to their instance data.  Objects are the only ones that
know about their instance data.  Other access to the instance data is done 
through the OODB services, which can provide pointer access to objects (for the
record/play capability, with the items to be recorded being configurable at 
run-time), or through direct requests for getting or setting the state of a 
given object.  Direct pointer access for record/play is required since some 
kind of look-up mechanism is needed to first find the objects, which is 
certainly not a "real-time" operation.

The only run-time overhead during the actual simulation run involves
pointer access, which we've found to be acceptable.