Re: User space

On Thu, 12 Feb 2004, Raul A Jager wrote:
>
> I need to share data between users.
>
> Can I use an "USER SPACE"?

Sure.


> Will the system allow several users updating it?

Yes, but IMHO, not gracefully.

>  when will the upates be seen by others?

As soon as they check for the updates.


A user space is similar to a file, except for three things:

a) It does not have any particular structure.

b) Since there are no records, there's no record locks, etc.

c) It's directly addressable with a pointer from an HLL program.
   (Technically, you can do that with any file, but you need to use MI
    tricks rather than normal HLL operations with non-userspaces)

The big problem is making sure that two jobs don't conflict with one
another.  You have to be very careful about any situation that could lead
to two processes writing data to it at the same time.

I recommend having the jobs communicate with each other using data queues
so that they can synchronize their operations -- preventing them from
conflicting with one another.

But, since they can send data to one another via the data queues, the
question becomes, do you still need the user space?   The only reason I
can think of why you'd want to use a user space for something like this
would be if the data that needs to be accessed is very large.  With a user
space they are sharing a common piece of information, but with data queues
the info is copied from one to the other -- so for very large pieces of
information, user spaces would be quicker.

Hope that makes sense...