[SNMP4J] Safely executing TreeUtils.getSubtree in concurrent threads

[Frank Fock]

Hi Nigel,

On Ubuntu I suspect that the agent is a NET-SNMP agent. It is then NOT 
multi-threaded.
Thus, you will get worse performance than expected if you concurrently 
access the same
agent with multiple-threads.

Best regards,
Frank

Am 19.06.2014 20:41, schrieb Nigel Thomas:
> Frank
>
> The client is mine. There is no separate agent - I am directly 
> addressing snmpd in ubuntu (on localhost at present, though eventually 
> it will be monitoring a distributed application running on a handful 
> of local servers). Traffic level should be reasonable - polling 
> hrStorageTable and hrSWRunTable every 30 seconds.
>
> I will investigate timeout changes tomorrow. Thanks and any more 
> suggestions always welcome
>
> Regards Nigel
>
>
>
>
> On 19 June 2014 19:30, Frank Fock <fock at agentpp.com 
> <mailto:fock at agentpp.com>> wrote:
>
>     Hi Nigel,
>
>     Your setup is absolutely fine and the recommended one for that task.
>     Have you checked that the agent isn't the problem?
>     Agents (except AGENT++ and SNMP4J-Agent based) are often single
>     threaded and many do not implement thread safe lexicographic ordering
>     correctly.
>
>     Also check the timeout values, because the agent will need more than
>     twice the time if polled concurrently from two threads (if not
>     multi-threaded).
>
>     Best regards,
>     Frank
>
>     Am 19.06.2014 19:32, schrieb Nigel Thomas:
>
>         Hi
>
>         I have a system with multiple threads getting different SNMP
>         subtrees from
>         the same target server concurrently using
>         TreeUtils.getSubtree. One thread
>         alone seems to work exactly as expected, but when a second
>         thread starts up
>         the two get confused; the first table receives no data.
>
>         Clearly I am having some sort of thread safety problem - but
>         with which
>         object/method? I am using
>         - a singleton instance of Snmp
>         - a single instance of CommunityTarget (for each monitored
>         server -
>         currently just localhost)
>         - therefore a single instance of TransportMapping - a
>         DefaultUdpTransportMapping; I have tried
>         setAsyncMsgProcessingSupported(true)
>         - a separate instance of TreeUtils per thread
>         - SNMPv2
>         - snmp4j-2.3.0
>
>         Any thoughts would be very welcome
>
>         TIA
>
>         Nigel
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