Counting semaphore

[v patel]

I would like to use reference counting while maintaining synchronization
among multiple processes.
I am looking into the feature of semaphore for this. Based on reading and my
sample program, I have
a couple of questions:

- Does this kernel object adjusts reference count to reflect abandonment by
one of the processes
holding a reference count exists abnormally, i.e. without calling
ReleaseReference()? My test
does not behave this way. I was expecting automatic invocation of
CloseHandle() by the kernel
to trigger this cleanup. If this is true, what specific steps are
necessary?

- If above is not true, is there any other mechanism to handle "Abandonment
Issue" without relying on
some sort of process monitoring service etc..

- Is there any way to get the current available count without
acquire/release on a semaphore?

thanks in advance,
vipul

[Le Chaud Lapin]

"v patel" <vipul...@intel.com> wrote in message news:<TG8ca.5431$io.2...@iad-read.news.verio.net>...

> - Does this kernel object adjusts reference count to reflect abandonment by
> one of the processes

No.

Closing a handle and changing the reference count are two different
things.

You might imagine a situation where there is a system-wide semaphore
that is waited on by 9 processes and set to its intial value by a
10th. The 10th process would have only one job - to set the initial
count of the semaphore and exit, but the programmer is sloppy so
CloseHandle will not be called before exit. The other 9 processes
would then contend for access to the semaphore based on the initial
value.

So you can see that it would be conceptually inappropriate for the OS
to adjust the reference count simply because the handle was not
closed.

Another way to look at it is to imagine that a process incremented a
sempahore 560 times, decrements 100, increments, 50, and decrements
70. Should the OS know to knock off 440 on the semaphore when the
process exits? What happens if, at the point of abnormal termination,
the semaphore is zero because the other processes snarfed all the
counts? Should the OS make the value -460?

> - If above is not true, is there any other mechanism to handle "Abandonment
> Issue" without relying on
> some sort of process monitoring service etc..

A good solution to this problem is C++ exception handling. Structure
your code so that if a hard exit occurs, the semaphore objects
automatically adjust reference count as necessary.

>
> - Is there any way to get the current available count without
> acquire/release on a semaphore?

Dunno. Your best bet is probabably to ask one of the kernel people.

-John-