Parallel UDP streaming - Githubissues

What steps will reproduce the problem?
1. Run single machine SAGE
2. Run parallel application with UDP

What is the expected output? What do you see instead?
Image freezes at the receiver (SAGE). But streamer keeps sending pixels in 
parallel.

What version of the product are you using?
The most recent developer version. Binary versions will show same symtom.

Please provide any additional information below.
LSU developed visualization program called eaviv. It does parallel rendering.
They want to stream imagery of from eaviv using SAIL to SAGE display wall.
In their setup SAGE was driven by single machine, and eaviv runs in parallel, 
streams with UDP.

Setup1 (Local Area)
2 senders (2 parallel render nodes) stream pixels to SAGE (laptop) through 1G 
links.
All machines are located within campus.

Setup2 (Wide Area)
Multiple senders (number varying up to 64) stream pixels to SAGE through 10G 
links.
Renders located at NCSA and SAGE is at LSU.

In both cases, the image size is 1000 x 1000 pixels.

Problem Description. (using Setup1)
When there are multiple senders stream to SAGE in parallel using UDP, image on 
the SAGE screen freezes. Senders keep streaming pixels but image is not 
updated. 
Also, sail prints out “sail received an invalid message” at the 
sail::parseMessage().

A link to youtube video showing their experiment is below. (Thanks to Sandeep)
http://www.youtube.com/watch?v=eNQ40Y4w_aY

If TCP is used, the parallel streaming works fine but very slow. (2 ~ 3 fps)
If only single renderer is used (no parallel stream), it works fine. (~ 15 fps)

Workaround.
Sandeep used qdisc (queueing discipline) to control UDP traffic (to alleviate 
UDP burstiness of SAIL), and parallel streaming works without freezing at least.
Original issue reported on code.google.com by schik...@gmail.com on 22 Nov 2010 at 8:01
ItayGal2 / sage-graphics

Parallel UDP streaming #22
