Subj : Boss Told Me You Can't Use Semaphore, But I Have To Do Something like It!
To   : comp.programming.threads
From : clusardi2k
Date : Tue Jul 12 2005 07:30 am

Hello,

   I have a assignment just thrown onto my desk by my boss who is
condescending at times. I'm lost! Am I missing something?

   Anyway, what is the easiest way to solve the below task. Do I
have alternatives. I'm looking for a detailed description and maybe
code!

   The job is:

   There are multible programs which use the same library routine
which is an interface to what I'll call a service program.

   The problem is that only 1 request at a time can be serviced by
the service program. The service program cannot be changed at all.

   My boss told me to just use somehting such as shared memory
(via memmap) and set a flag in there to 1 when a program wants
service. The various programs are to wait in a loop until that
flag becomes 0 or a time-out occurs. If the flag becomes 0 then
one process will set it to 1 along with setting other parameters
to send to the service program. If a process times-out it will
return without receiving any service. But, if a process received
service the process will set the flag to 0 for the next process.

   The problem is, woun't this lead to programs setting that
shared memory flag to 1 at the same time causing an eventual loss
of service etc. I.E.:They clobber each other.

   The way I see it is the flag described above is a critical
section and must be protected by a mutual exclusion semaphore.

   I don't see anything wrong with using shared memory for sending
parameters to the service routine.

   My boss says I am not allowed to use semaphores due to
unexplained reasons.

   O'kay what should I do? 

   Thank you, 
   Christopher Lusardi

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