PS> I'm currently developing a BBS system, and of course - 
 PS> multinode. This means 

I'll do that later.  ;-)

 PS> that there will be multiple threads or processes (depending on how I'll 
 PS> implement it) be accessing the same files! Let's take the message-files 

Recommendation: Use seperate processes.
  Cons:
        Processes take more resources to keep going
  Pros:
        One node crashing doesn't take down the ENTIRE BBS.

To access multiple files, use sharing.  One option is sopen - not ANSI,
IIRC, but available in many compilers (Watcom included).  The other option
is to use DosOpen directly (I would recommend writing some sort of io
library to go with it just in case you want to port to AIX or something -
then you just rewrite the library rather than everything else).

Actually, another option that I would consider is a server/client version
of a BBS - set up a server to communicate with via pipes, and each node
will just ask the server.  The server would then co-ordinate everything.
  Cons:
        Take even MORE resources to keep going - a single server, in
addition to everything else.
        Server crashing will take down the entire BBS.
        Server is almost useless unless you have multiple processes rather
than multiple threads for each node.
  Pros:
        You could allow users, say on a WAN, LAN, or even internet, to have
a BBS and let the server do the access restrictions... and never worry
about having somebody do something awful to the system.  :-)  
        It also lends itself to serialization a little better between the nodes.

This can be simplified somewhat... you'd lose the ability to allow users to
have client versions of the BBS (well, without writing an intermediate
"server/client"), but it would be much easier: Use DB2 or some
other multi-threaded multi-system share-aware database that is pre-built. 
I may end up just using DB2/2 myself.  :-)
  Cons:
        Cost.
  Pros:
        Bug-free code.
        Sharing, etc., is already done - no coding required.
        Expandability (since these will have been built as generic DB's in
the first place).

 PS> and file-files for instance. If 4 nodes wishes to read/write to the same 
 PS> message/file-base (thus, the same file), how do I 
 PS> coordinate this? Semphores' 
 PS> not good, considering there could be 100 nodes running (unlikely, but 50 

Semaphores would still be good for 100 nodes... I'm sure sharing does the
same thing anyway.

 PS> maybe). Of course I could make the program try to open 
 PS> the file until it is 
 PS> allowed access, but that doesn't seem very effective. 

I believe that if you try to open a file that you're denied, you can ask
DosOpen to wait until it's available...



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