Thursday, September 13, 2007

September 5th Report

Demo is ready.

ROOT application development supports both interpreted code and also compiled code. Interpreted code (Mainly the analysis code written by physicist) can use compiled shared libraries including ROOT provide ones and also other user written libraries. Interpretation helps the user to debug and fix code easily and write the necessary analysis as a function.

As explained in my previous blog (August 22nd Report) the plan is to let the rootlet to publish the location of the generated histogram files to the subscribed clients. Clients who receive those notifications then use these files to update their results.

As the second phase, I developed a ROOT compliant wrapper classes for the C++ client of Naradabrokering. These allow ROOT clients to utilize the publish/subscribe capabilities of Naradabrokering.
The steps for developing the ROOT compliant classes are explained in the following tutorial.
Part1, part2 and part3

I was able to get the publishing of messages working from interpreted code and thought that the subscription would work in the same manner. After few days of trying I found that I was wrong.
To get the subscription to work, the interpreted code should pass a function pointer as the callback to the compiled code and on the reception of a notification , the compiled code should call this callback (which is in the interpreted code). Passing a function pointer to the compiled code is easy and straight forward, however, when the compiled code try to call that pointer I got an error *****Segmentation Violation*********

This happens mainly because of the limitation of the ROOT interpreter in resolving function pointers across the interpreted/compiled code boundaries. After few days of searching and querying Conrad, we decided to ask the question on the ROOT mailing list. They replied really soon and helped us to solve the problem. The solution came in a way of a reflection type call interface for calling interpreted code from the compiled code supported by ROOT.
Here is the mail thread.

So with that help, I was able to get the demonstration working and it is so nice to see how it is working. Results of the remote analysis triggers users who are subscribed for notifications and their histograms get updated with remote results.

Somethings are too good to be true!