Re: Semaphore / Synchronizing write operations

Is there any example where I can look?
I'm having some trouble implementing the spinloclk mechanism!

>> Each application would retrieve the contents of the table > together with
>> this semaphore value  (as a single SNMP request).   :

To retrive table values I do :
    snmpbulkwalk -v2c -Os -c public localhost  applicationTypeTable

How can I change this command to retrive the spinlock value?

Thanks in advance.

----- Original Message ----- 
From: "Dave Shield" <[email protected]>
To: "vsaavedra" <[email protected]>
Cc: <[email protected]>
Sent: Wednesday, October 17, 2007 9:34 AM
Subject: Re: Semaphore / Synchronizing write operations


> On 16/10/2007, vsaavedra <[email protected]> wrote:
> > My problem is: When two applications try to update de MIB at same time,
it's
> > possible that one application rewrite the data that other application
just
> > wrote.
> >
> > How can I guarantee that two applications can't update the same node at
the
> > same time.
>
> The usual SNMP mechanism for implementing this would be a MIB
'TestAndIncr'
> object.   Each application would retrieve the contents of the table
> together with
> this semaphore value  (as a single SNMP request).   They would then issue
a
> SET request, containing the new table values and this same semaphore value
> (again, as a single SNMP request).
>
> The first client would be providing the same semaphore value as the one
read,
> so the SET request would succeed (incrementing the internal semaphore
value).
> The second client would now be providing an out-of-date semaphore value,
> so the SET request would be rejected.
>
> There is a helper routine
>     int  netsnmp_register_watched_spinlock(
>                                netsnmp_handler_registration *reginfo,
> int *spinlock);
>
> to implement just such a semaphore object.
>
> Dave
>
> [This response has been saved as a Good Answer on the project wiki pages
>
http://www.net-snmp.org/wiki/index.php/Prevent_two_clients_from_making_conflicting_updates
> ]
>
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