RE: EDM Freeze Problem Resolved

["Chestnut, Ronald P." <ronc@slac.stanford.edu>]

Ok, I'll bite --- why 11? 


Ron Chestnut 


-----Original Message-----
From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Brian Bevins
Sent: Wednesday, March 11, 2009 9:01 AM
To: EPICS Techtalk
Subject: EDM Freeze Problem Resolved

Back in January I described a problem we have been having with EDM ever since we moved from HP-UX to RedHat Enterprise Linux in 2006. It was serious enough to prevent us from completing our Linux deployments in some areas. With help from John this has now been resolved.

The problem was that operators would sometimes find at random times that their EDM displays were showing old data that didn't match displays on other workstations. In fact, the EDM screens were completely frozen with no graphical updates. Opening or closing a display would always resolve the problem, but for a long time we couldn't reproduce it deliberately.

To help us diagnose the problem, John added an option in EDM 1-11-1zm that allows you to set an environment variable EDMIGNOREICONIC that causes EDM to ignore the iconified state of windows. That is, with the variable set, all widgets get updated even if the window manager reports that the window is iconified. This made our frozen screen problem go away and pointed me to the source of the problem. There is a bug in the code that checks windows for their iconified state.

Using EDM 1-11-1zm or later with EDMIGNOREICONIC avoids the problem. I have sent John a patch for his review that corrects the bug and eliminates the need for setting EDMIGNOREICONIC.

To see the bug in action (or lack thereof) you need to open a number of EDM displays that is a multiple of 11. Make sure that at least one display is on a different desktop workspace (which is equivalent to being iconified under many window managers). Once the 11th display is open, switch workspaces and you will find that any displays that were on other workspaces are now frozen. Opening or closing a display will unfreeze all the displays (since the total is no longer 11). Note that when counting the open displays, embedded displays count separately. So, for example, a single EDM window that contains 3 embedded displays will count as 4 displays total. We have observed this on RHEL 3, 4, and 5 using GNOME or KDE. There are also reports of it on Scientific Linux and Debian. We did not see the problem using CDE on HP-UX probably due to different window/workspace handling.

My hearty thanks to John for helping us track this down and to all of the operators here who diligently reported the problem with enough detail to finally nail it.

--Brian

--
Brian S. Bevins, PE
Computer Scientist / Mechanical Engineer Thomas Jefferson National Accelerator Facility

     "Nothing in all the world is more dangerous than
      sincere ignorance and conscientious stupidity."
                                     --Martin Luther King Jr.