Event based DA on OPC Server.

[Atul Prasad]

Hi, Happy New Year to everyone.
I am trying to connect to OPC server through the Java client which I intend to run on Linux. I am using UTGARD openscada library  for my Java Client.
Unfortunately, the openscada documentation is very sparse, and usage explanation are hard to come by.
I am mainly relying on the API docs here, http://neutronium.openscada.org/javadoc/1.3/milestone/
I am basically trying to use Async20Access class to use Event based notification functionality. I am using Async20Access.addItem() to individually add each DA variable to their callbacks. I expect the callbacks to be called whenever a variable has changed, however the behavior is not the same. I get 2 reads on the variable with constructing AccessBase following way.
final AccessBase access = new Async20Access(server, 500000, false);
After 2 reads of the same variable, it craps out with the exception

     18:11:06.884 [jI_OxidResolver_Client[55612 , 58728]] WARN  o.j.dcom.core.JIComOxidRuntimeHelper - Oxid Resolver Thread/run
           java.io.IOException: Socket Closed

Am I using the right Access class and in the right way? Is Async20Access the right class to be used for (changed) event based OPC data access. Is there more document on the usage of classes, I'd appreciate if you can point me to it.
I have poured over the wiki
https://openscada.atlassian.net/wiki/display/OP/How-To+Articles
Thanks,

[Jens Reimann]

Hi,

so in short, the remote side closed the connection. But I cannot tell you why, this decision is made by the remote side (Windows).

I would suggest to use the sync access method. It is much more stable.

Jens

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[Atul Prasad]

Thanks for the response Jens.
Scouring this board, i learnt that to use event based DA, I have to attach IOPCDataCallback callback to the group. I am yet to try it though.
My question to you is if there is a better way(documentation/demo code) to learn how to use openscada library to do such things beyond basic Howto guide present on the wiki. If so , can you point me to it.
Thanks,

[Jens Reimann]

Not really sorry.

But if you have any questions I will try and help you.

Jens