On 07/12/2007, Giuseppe Modugno <[EMAIL PROTECTED]> wrote:
> What is the use of a watcher variable?
The idea of the watcher helper is as follows:
Some MIB objects may need quite complex processing to retrieve
the current value or (particularly) to respond to the assignment of a
new value. But other MIB objects may simply be monitoring (or
updating) some value that is already implemented in your application
as a distinct data variable.
In this situation, all that the agent needs to do is "watch" this
variable, and report (or update) the current value whenever it receives
a request for that particular OID.
That's the purpose of the watcher helper. You provide it with the
location of the variable that holds this value, and the OID associated
with this MIB object. And the helper does the rest.
As a fer-instance:
Suppose you're monitoring a web server, and want to know how many
connections are being actively processed at any one time. One approach
would be to retrieve the current status of each webserver process or
thread, and count up the number that are currently active. That involves
a reasonable amount of processing, so you would need to code a MIB
handler to do this.
But it's quite possible that the main web server process already holds
this information (so that it knows whether to find an idle server process,
start up another child, or hold the HTTP request in a queue). So if there
is a variable within the web server that holds this values, and you point
the watcher helper at this variable (specifying the appropriate OID) - then
that automatically implements the required behaviour. No special code
is needed.
Is that any clearer?
Dave
-------------------------------------------------------------------------
SF.Net email is sponsored by:
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://sourceforge.net/services/buy/index.php
_______________________________________________
Net-snmp-coders mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/net-snmp-coders
