Re: Using Global Variables

[agate!linus!linus.mitre.org!giddings.mitre.org!user@ucbvax.Berkeley.EDU (Victor Giddings)]

In article <1992Sep22.201420.25962@swlvx2.msd.ray.com>, lms@swl.msd.ray.com
(LEE MARDEN) wrote:
> 
> 
>   At the risk of being flamed for continuing to beat a dead horse, could some
> summarize the methods available (good and bad) for using shared memory.  I
> just started to monitor comp.lang.ada and have a specific problem I'm trying
> to solve.  Here goes:  I have a 4D/240 Power series Silicon Graphics computer
> running Irix 4.0.1 (Unix) and the Verdix Ada compiler (on order).  The comput
er
> has 4 processors.  The plan is to reuse code as much as possible so I'm 
> stuck with one processor running C, another Fortran and the other two Ada.
> Each processor needs to communicate with the others.  I'm not sure on the
> amount of data, but my first guess would be tons(>1k variables).  My initial
> investigate has only lead me to the conclusion that I would have to write
> some Ada wrappers around the C routines (shmctl, shmop, shmget) to control
> a shared memory chunk, 

We actually experimented with this with some success (although I still
think it was a bad idea).  We did, however, have unexplained intermittent
crashes.  We speculated that the shmat (using shmaddr:= 0) was returning an
address that the run-time system was re-using for a dynamic allocation. 
Any SGI and/or Verdix gurus wish to comment?

> and that all I would get is a pointer to the data
> space.  That would make data access very clumsy. 
The indirection can be accomplished using one qualification, e.g.
Global_Pool.Data_Element.  Doesn't strike me as any more clumsy than trying
to maintain the data space in the first place.  :-)

> I've heard of some Pragmas
> on other systems that allow you to specify that an entire package of variable
s
> be shared, and utilities to perform the maintance thereof.  I hope that's
> enough info for someone to respond.  If not, let me know and I'll elaborate
> (no pun intended).
> 
>  AdvThanksance, Lee Marden
>  
> -- 
>   AdvThanksance,
> 
>   Lee S. Marden, lms@swlray.msd.ray.com
>   Raytheon Company, Missile Systems Division, Tewksbury, MA 01876