Improvement of the ALICE Online Event Display using OO patterns and - - PowerPoint PPT Presentation

Amsterdam, CHEP 14-18 October 2013 1

Improvement of the ALICE Online Event Display using OO patterns and parallelization techniques

Mihai Niculescu (Institute of Space Science Romania) for ALICE experiment

Amsterdam, CHEP 14-18 October 2013 2

A bit of History (1/2)

• ALICE Event Display

(alieve) was mainly developed by Matevz Tadel and Alja Mrak-Tadel

• Experiment dependent: data

loading and processing algorithms:

– Detector geometry,

simulation & reconstructed data

– Raw and digits data – High-level trigger

events

– Visualization scripts

Amsterdam, CHEP 14-18 October 2013 3

A bit of History (2/2)

• Experiment independent code was ported to ROOT (REVE) –

GUI and OpenGL – now part as a ROOT module

– Application core

• Management: obj-browsers, 3D scenes and

viewers, events and event navigation

• Environment for CINT scripts

– Visualization classes (geometry,extracted shape

data, hits,clusters, tracks)

Amsterdam, CHEP 14-18 October 2013 4

The Online Story

• In Online mode we want to be able to visualize events as they

come, this brings coolness

• Also, proves as a good visual tool for debugging (acquisition,

detector algorithms, reconstruction processing chain)

• Basically, in online mode:

– 1. Fetch the raw data event – 2. Reconstruct it – 3. Display it – 4. go to 1 or exit if no more events

Amsterdam, CHEP 14-18 October 2013 5

The Online Plot

rec.C (Reconstruction) Fork process DIM client /process mngr DIM server 146860 *Below same thing in words

Amsterdam, CHEP 14-18 October 2013 6

The Online Conflict

• AliEve (visualization) is coupled with reconstruction (data

model) – CINT hooks in the reconstruction to call alieve:

– No good design – AliEve GUI freezes while reconstruction runs

• Can't change viz. Options/params
• Can't take screenshots

– If reconstruction crashes, so do the visualization

(alieve)

• Only one single application (alieve) to visualize the online

reconstructed data

Amsterdam, CHEP 14-18 October 2013 7

The Online Climax

• Proposed solutions, make use of:

– HLT Homer protocol

• Reliable & uses TSockets from ROOT

– Network sockets

• Pure posix C API
• TSockets: ROOT network API
• ZeroMQ

– Network file sharing environment

Amsterdam, CHEP 14-18 October 2013 8

A bit about ZeroMQ library

• Intelligent and small socket library for messaging
• Very fast (8 M msg/sec, 30 micro sec latency)

– “It's sockets on steroids”

• Many kinds of messaging patterns (Pub/Sub, Req/Rep,

Req/Router, Dealer/Rep, Push/Pull, etc.)

• Licensed under LGPL
• Multiple transports (inproc, ipc,tcp,pgm)
• Multi-platform (Windows, Linux, Android,..)
• Automatically deals with socket failures - (re)connect
• Easy to learn and implement

Amsterdam, CHEP 14-18 October 2013 9

Improvement of Online event display

• Created an event server with a GUI
• Listens for DIM messages
• contains an online reconstruction server in a separate thread

– Reconstructs the incoming raw events – Create the TStreamerInfos of AliESDEvent – Serialize AliESDEvent – Send both to a 0MQ socket as a multi-part message

• Multiple clients can subscribe to this socket
• View is decoupled from model/controller

Amsterdam, CHEP 14-18 October 2013 10

Future goals

• Implement the pattern REQUEST-REPLAY in order to fetch

previous reconstructed events from the server

• Implement a superuser mode in order to bookmark/save

interested events

• Serve events in a different data format (XML,...) to allow clients

be independent of ROOT

– Clients written with HTML5, iOS SDK,

Android,...

Amsterdam, CHEP 14-18 October 2013 11

Acknowledgements

• Peter Hristov (CERN) and Andrei Gheata (CERN) for all helpful

comments/ideas

• Gerardo Ganis (CERN) for making sense of streamer infos
• Miguel Martinez Pedreira (CERN, office mate) for convincing

me to use ZeroMQ

Amsterdam, CHEP 14-18 October 2013 12

Thank you for your attention!