Experimental Physics and
Industrial Control System

John Sinclair <[email protected]> · Wed, 11 Mar 2009 12:39:50 -0400

A new release incorporating Brian's fix is on the website.

http://ics-web.sns.ornl.gov/edm/info/show.php?mon=Mar&theDay=11&year=2009

John Sinclair

Brian Bevins wrote:

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