Re: Semaphor

On 4/3/06, Elvis Budimlic <ebudimlic@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Semaphore is inter-process synchronization object popular on other platforms
> and is finding its way to System i world via cross-platform ERP applications
> and programmers.
> It can be used for locking purposes, much like mutex or object lock.  It can
> also be used for resource accounting.  It's simply an integer value in an
> array of integers (semaphore set).  It can have a max value, so say when you
> only want 7 people to print to the printer, you can set the max value to 7
> so next time your application requests a semaphore it'll have to wait until
> one of those original 7 releases its own handle (decrements integer count by
> 1).
> So, it's purely a synchronization object used by application programmers.
> It has its use and is very nice mechanism when used appropriately by the
> developer.  When not, bad things happen (i.e. requests back up).
>
> I've seen some of these issues occasionally with one ERP solution and is
> usually caused by administrators running multiple tasks that conflicted with
> each other.
>
> <vendor plug>
> We've developed a tool that lets you look at jobs in SEMW (semaphore wait)
> state and get all the details you'll need on it (like who posted to it last
> - i.e. who didn't post back and release the 'lock').

That is pretty neat!  I know that win32 semaphores dont store the id
of the processes that have locked it.  Is it a feature of Unix that
allows your product to determine which job has locked the semaphore?

-Steve